MAX1540AETJ+T ,Dual Step-Down Controllers with Saturation Protection, Dynamic Output, and Linear RegulatorApplications♦ Overvoltage/Undervoltage-Protection OptionNotebook Computers♦ 1.7ms Digital Soft-Star ..
MAX1540ETJ ,Dual Step-Down Controllers with Saturation Protection, Dynamic Output, and Linear RegulatorApplications♦ Overvoltage/Undervoltage-Protection OptionNotebook Computers♦ 1.7ms Digital Soft-Star ..
MAX1540ETJ ,Dual Step-Down Controllers with Saturation Protection, Dynamic Output, and Linear RegulatorMAX1540/MAX154119-2861; Rev 2; 1/05Dual Step-Down Controllers with SaturationProtection, Dynamic Ou ..
MAX1540ETJ ,Dual Step-Down Controllers with Saturation Protection, Dynamic Output, and Linear RegulatorFeatures♦ Inductor-Saturation ProtectionThe MAX1540/MAX1541 dual pulse-width modulation(PWM) contro ..
MAX1540ETJ+ ,Dual Step-Down Controllers with Saturation Protection, Dynamic Output, and Linear RegulatorFeatures♦ Inductor-Saturation ProtectionThe MAX1540/MAX1541 dual pulse-width modulation(PWM) contro ..
MAX1541 ,Dual Step-Down Controllers with Saturation Protection, Dynamic Output, and Linear RegulatorApplications Overvoltage/Undervoltage-Protection OptionNotebook Computers 1.7ms Digital Soft-Star ..
MAX417ESA ,1.2microA max, dual, single-supply op amp.ELECTRICAL CHARACTERISTICS
(V+ = 2.5V, V- = -2.5V, TA = +25°C, unless otherwise noted.)
PARAMET ..
MAX417ESA+ ,Single, Dual, Quad, 1.2µA Max, Single-Supply Op AmpsELECTRICAL CHARACTERISTICS (continued)
_ = 25N, v, = Al bv, TA = 425°C. unlsss otherwise noted.) ..
MAX417ESA+T ,Single, Dual, Quad, 1.2µA Max, Single-Supply Op AmpsELECTRICAL CHARACTERISTICS (continued)
_ = 25N, v, = Al bv, TA = 425°C. unlsss otherwise noted.) ..
MAX4180ESA ,Single/Dual/Quad / 270MHz / 1mA / SOT23 / Current-Feedback Amplifiers with ShutdownFeaturesThe MAX4180 family of current-feedback amplifiers' Ultra-Low Supply Current: 1mA per Amplif ..
MAX4180EUT+T ,Single/Dual/Quad, 270MHz, 1mA, SOT23, Current-Feedback Amplifiers with ShutdownFeaturesThe MAX4180 family of current-feedback amplifiers♦ Ultra-Low Supply Current: 1mA per Amplif ..
MAX4182ESA ,Single/Dual/Quad / 270MHz / 1mA / SOT23 / Current-Feedback Amplifiers with ShutdownApplicationsTEMP. PIN- SOTPARTPortable/Battery-Powered High-Definition RANGE PACKAGE TOP MARKVideo/ ..
MAX1540AETJ+-MAX1540AETJ+T-MAX1541ETL+-MAX1541ETL+T
Dual Step-Down Controllers with Saturation Protection, Dynamic Output, and Linear Regulator
General DescriptionThe MAX1540A/MAX1541 dual pulse-width modulation
(PWM) controllers provide the high efficiency, excellent
transient response, and high DC-output accuracy nec-
essary for stepping down high-voltage batteries to gen-
erate low-voltage chipset and RAM power supplies in
notebook computers.
The Maxim proprietary Quick-PWM™ controllers are
free running, constant on-time with input feed forward.
This configuration provides ultra-fast transient
response, wide input-output (I/O) differential range, low
supply current, and tight load-regulation characteris-
tics. The controllers can accurately sense the inductor
current across an external current-sense resistor in
series with the output to ensure reliable overload and
inductor saturation protection. Alternatively, the con-
trollers can use the synchronous rectifier itself or loss-
less inductor current-sensing methods to provide
overload protection with lower power dissipation.
For a single step-down PWM controller with inductor-
saturation protection, external-reference input voltage,
and dynamically selectable output voltages, refer to the
MAX1992/MAX1993 data sheet.
ApplicationsNotebook Computers
Core/I/O Supplies as Low as 0.7V
0.7V to 5.5V Supply Rails
CPU/Chipset/GPU with Dynamic Voltage Core
Supplies (MAX1541)
DDR Memory Termination (MAX1541)
Active Termination Buses (MAX1541)
FeaturesInductor-Saturation ProtectionAccurate Differential Current-Sense InputsDual Ultra-High-Efficiency Quick-PWMs with
100ns Load-Step ResponseMAX1540A
1.8V/1.2V Fixed or 0.7V to 5.5V Adjustable
Output (OUT1)
2.5V/1.5V Fixed or 0.7V to 5.5V Adjustable
Output (OUT2)
Fixed 5V, 100mA Linear RegulatorMAX1541
External Reference Input (REFIN1)
Dynamically Selectable Output Voltage—0.7V
to 5.5V (OUT1)
2.5V/1.8V Fixed or 0.7V to 5.5V Adjustable
Output (OUT2)
Optional Power-Good and Fault Blanking
During Transitions
Fixed 5V or Adjustable 100mA Linear Regulator1% VOUTAccuracy over Line and Load2V to 28V Battery Input Range170kHz to 620kHz Selectable Switching
FrequencyOvervoltage/Undervoltage-Protection Option1.7ms Digital Soft-StartDrives Large Synchronous-Rectifier FETs2V ±0.7% Reference OutputSeparate Power-Good Window Comparators
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
THIN QFNTOP VIEW
MAX1540A
ON1
ON2
CSP1
CSN1
FB1
OUT1
PGOOD1DH1
CSP2
CSN2
FB2
OUT2
PGOOD2
DH2
LX2BST2181920212223
GNDDL2V+LDOOUTDL1LDOONBST1765432
REF
ILIM2ILIM1
VCC
TON
LSAT
SKIP
OVP/UVP
LX1
A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES.
Pin Configurations19-2861; Rev 3; 2/07
EVALUATION KIT
AVAILABLE
Ordering Information
PARTTEMP RANGEPIN-
PACKAGE
PKG
CODE
MAX1540AETJ-40°C to +85°C32 Thin QFN
5mm x 5mmT3255-4
MAX1540AETJ+-40°C to +85°C32 Thin QFN
5mm x 5mmT3255-4
MAX1541ETL-40°C to +85°C40 Thin QFN
6mm x 6mmT4066-5
MAX1541ETL+-40°C to +85°C40 Thin QFN
6mm x 6mmT4066-5
Pin Configurations continued at end of data sheet.
+Denotes a lead-free package.
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
ABSOLUTE MAXIMUM RATINGSStresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Note 1:For the MAX1540A, the gate-driver input supply (VDD) is internally connected to the fixed 5V linear-regulator output
(LDOOUT), and the linear-regulator input supply (LDOIN) is internally connected to the battery voltage input (V+).
V+, LDOON to GND...............................................-0.3V to +28V
LDOOUT to GND (MAX1540A, Note 1)....................-0.3V to +6V
LDOOUT to GND (MAX1541, Note 1)....................-0.3V to +28V
VDDto GND (MAX1541, Note 1)..............................-0.3V to +6V
VCC, ON_ to GND.....................................................-0.3V to +6V
SKIP, PGOOD_ to GND............................................-0.3V to +6V
FB_, CSP_, ILIM_ to GND.........................................-0.3V to +6V
TON, OVP/UVP, LSAT to GND...................-0.3V to (VCC+ 0.3V)
REF, OUT_ to GND.....................................-0.3V to (VCC+ 0.3V)
LDOIN to GND (MAX1541).....................................-0.3V to +28V
REFIN1, GATE, OD, FBLDO to GND (MAX1541).....-0.3V to +6V
FBLANK, CC1 to GND (MAX1541).............-0.3V to (VCC+ 0.3V)
DL_ to GND (Note 1)..................................-0.3V to (VDD+ 0.3V)
CSN_ to GND............................................................-2V to +30V
DH_ to LX_..................................................-0.3V to (BST + 0.3V)
LX_ to GND................................................................-2V to +30V
BST_ to LX_..............................................................-0.3V to +6V
REF Short Circuit to GND...........................................Continuous
Continuous Power Dissipation (TA= +70°C)
32-Pin 5mm x 5mm Thin QFN (derated 21.3mW/°C
above +70°C).............................................................1702mW
40-Pin 6mm x 6mm Thin QFN (derated 26.3mW/°C
above +70°C).............................................................2105mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
ELECTRICAL CHARACTERISTICS(V+ = 15V, VCC= VDD= ON1 = ON2 = 5V, SKIP= GND, LDOIN (MAX1541) = V+, TA
= 0°C to +85°C, unless otherwise noted. Typicalvalues are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
INPUT SUPPLIES (Note 1)MAX1540A: battery voltage, V+ > VLDOOUT5.528VINMAX1541: battery voltage, V+ > VLDOOUT228
VBIASVCC, VDD (MAX1541)4.55.5Input Voltage Range
VLDOINMAX1541: LDO input supply,
VLDOIN > VLDOOUT4.528
FB1 and FB2 forced above the regulation
point, LSAT = GND0.71.5
Quiescent Supply Current (VCC)ICC
FB1 and FB2 forced above the regulation
point, ON1 or ON2 = VCC, VLSAT > 0.5V1.8
Quiescent Supply Current
(VDD, MAX1541 Only)IDDFB1 and FB2 forced above the regulation
point, ON1 or ON2 = VCC<15µA
MAX1540A: FB1 and FB2 forced above the
regulation point, ON1 or ON2 = VCC,
VLDOON = V+ = 28V
Quiescent Supply Current (V+)IV+
MAX1541: ON1 or ON2 = VCC,
VLDOON = V+ = 28V2540
Quiescent Supply Current
(LDOIN, MAX1541 Only)ILDOIN
FB1 and FB2 forced above the regulation
point, ON1 or ON2 = VCC,
VLDOON = V+ = 28V
110µA
Standby Supply Current (VCC)ON1 = ON2 = GND, VLDOON = V+ = 28V<15µA
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC= VDD= ON1 = ON2 = 5V, SKIP= GND, LDOIN (MAX1541) = V+, TA
= 0°C to +85°C, unless otherwise noted. Typicalvalues are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSStandby Supply Current
(VDD, MAX1541 Only)ON1 = ON2 = GND, VLDOON = V+ = 28V<15µA
MAX1540A: ON1 = ON2 = GND,
LDOON = V+ = 28V, VCC = 0 or 5V105
Standby Supply Current (V+)
MAX1541: ON1 = ON2 = GND,
LDOON = V+ = 28V, VCC = VDD = 0 or 5V<15
Standby Supply Current
(LDOIN, MAX1541 Only)ON1 = ON2 = GND, VLDOON = V+ = 28V100µA
Shutdown Supply Current (VCC)ON1 = ON2 = LDOON = GND<15µA
Shutdown Supply Current
(VDD, MAX1541 Only)ON1 = ON2 = LDOON = GND<15µA
MAX1540A: ON1 = ON2 = LDOON = GND,
V+ = 28V, VCC = 0 or 5V415
Shutdown Supply Current (V+)MAX1541: ON1 = ON2 = LDOON = GND,
V+ = 28V, VCC = VDD = 0 or 5V<15
Shutdown Supply Current
(LDOIN, MAX1541 Only)LDOON = GND410µA
PWM CONTROLLERSFB1 = GND1.7821.801.818
VOUT1
Preset output,
V+ = 5.5V to 28V,
SKIP = VCCFB1 = VCC1.1881.201.212MAX1540A Main Output-Voltage
Accuracy (OUT1) (Note 2)
VFB1Adjustable output, V+ = 5.5V to 28V,
SKIP = VCC0.6930.700.707
FB2 = GND2.4752.502.525
VOUT2
Preset output,
V+ = 5.5V to 28V,
SKIP = VCCFB2 = VCC1.4851.501.515MAX1540A Secondary Output-
Voltage Accuracy (OUT2)
(Note 2)
VFB2Adjustable output, V+ = 5.5V to 28V,
SKIP = VCC0.6930.700.707
MAX1541 Main Feedback-
Voltage Accuracy (FB1)VFB1V+ = 4.5V to 28V,
SKIP = VCCREFIN1 = 0.35 x REF0.6930.700.707V
FB2 = GND2.4752.502.525
VOUT2
Preset output,
V+ = 4.5V to 28V,
SKIP = VCCFB2 = VCC1.7821.801.818MAX1541 Secondary Output-
Voltage Accuracy (OUT2)
(Note 2)
VFB2Adjustable output, V+ = 4.5V to 28V,
SKIP = VCC0.6930.700.707
Load-Regulation ErrorILOAD = 0 to 3A, SKIP = VCC0.1%
Line-Regulation ErrorVCC = 4.5V to 5.5V, V+ = 4.5V to 28V0.25%
FB_ Input Bias CurrentIFB_-0.1+0.1µA
Output Adjust Range0.75.5V
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC= VDD= ON1 = ON2 = 5V, SKIP= GND, LDOIN (MAX1541) = V+, TA
= 0°C to +85°C, unless otherwise noted. Typicalvalues are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSFB_ = GND70145350
MAX1540AFB_ = VCC or
adjustable50115220
FB1 = OUT14007001500
FB2 = GND90170350
OUT_ Input ResistanceROUT_
MAX1541
FB2 = VCC or
adjustable60130270
OUT_ Discharge Mode On-
ResistanceRD IS C H ARGE 1025Ω
OUT_ Synchronous-Rectifier
Discharge-Mode Turn-On Level0.20.30.4V
Soft-Start Ramp TimetSSRising edge on ON_ to full current limit1.7ms
TON = GN D ( 620kH z) 149169190
TON = REF (485kHz)191216242
TON = op en ( 345kH z) 274304335DH1 On-TimetON1
V+ = 15V,
VOUT1 = 1.5V
(Note 3)
TON = VCC (235kHz)402447491
TON = GN D ( 460kH z) 201228256
TON = REF (355kHz)260296331
TON = op en ( 255kH z) 371412453DH2 On-TimetON2
V+ = 15V,
VOUT2 = 1.5V
(Note 3)
TON = VCC (170kHz)556618679
On-Time TrackingtON2 with respect to tON1 (Note 3)120135150%
Minimum Off-TimetOFF(MIN)(Note 3)400500ns
LINEAR REGULATOR (LDO) (Note 1)0 < ILDOOUT < 10mA4.855.05.10MAX1540A LDO Output-Voltage
AccuracyVLDOOUTON1 = ON2 = GND,
V+ = 6V to 28V0 < ILD OOU T < 100m A4.705.10V
0 < ILDOOUT < 10mA4.855.05.10MAX1541 LDO Output-Voltage
Accuracy (Fixed VLDOOUT)VLDOOUT
FBLDO = ON1 =
ON2 = GND,
VLDOIN = 6V to 28V0 < ILD OOU T < 100m A4.705.10
0 < ILDOOUT < 10mA1.2121.251.275MAX1541 LDO Feedback
Accuracy (Adjustable VLDOOUT)VFBLDO
FBLDO = LDOOUT,
ON1 = ON2 = GND,
VLDOIN = 4.5V to
28V0 < ILD OOU T < 100m A1.1751.275
MAX1541 LDO Output
Adjust Range1.17524V
LDOOUT Short-Circuit Current130mA
FBLDO Input Bias CurrentIFBLDO-0.1+0.1µA
MAX1540A: V+ - VLDOOUT, ILDOOUT = 50mA500800
Dropout VoltageMAX1541: VLDOIN - VLDOOUT,
ILDOOUT = 50mA500800mV
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC= VDD= ON1 = ON2 = 5V, SKIP= GND, LDOIN (MAX1541) = V+, TA
= 0°C to +85°C, unless otherwise noted. Typicalvalues are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
REFERENCE (REF)TA = + 25° C to + 85° C 1.9862.002.014Reference VoltageVREFVCC = 4.5V to 5.5V,
IREF = 0VTA = 0° C to +85°C1.9832.002.017V
Reference Load RegulationΔVREFIREF = -10µA to +50µA-0.01+0.01V
REF Lockout VoltageVREF(UVLO)Rising edge, hysteresis = 350mV1.95V
REFIN1 (MAX1541)
Voltage RangeVREFIN0.7VREFV
REFIN1 (MAX1541)
Input Bias CurrentIREFIN10.010.05µA
FAULT DETECTIONOvervoltage Trip ThresholdWith respect to error-comparator threshold,
OVP/UVP = VCC121620%
Overvoltage Fault-Propagation
DelaytOVPFB forced 2% above trip threshold10µs
Output Undervoltage-Protection
Trip Threshold
With respect to error-comparator threshold,
OVP/UVP = VCC657075%
Output Undervoltage-Protection
Blanking TimetBLANKFrom rising edge of ON_1035ms
Output Undervoltage Fault-
Propagation DelaytUVP10µs
PGOOD_ Lower Trip ThresholdWith respect to error-comparator threshold,
hysteresis = 1%-13-10-7%
PGOOD_ Upper Trip ThresholdWith respect to error-comparator threshold,
hysteresis = 1%+7+10+13%
PGOOD_ Propagation DelaytPGOOD_FB forced 2% beyond P GOOD _ trip threshold10µs
PGOOD_ Output Low VoltageISINK = 4mA0.3V
PGOOD_ Leakage CurrentIPGOOD_FB = REF (PGOOD high impedance),
PGOOD forced to 5.5V1µA
FBLANK = VCC120220320
FBLANK = open80140205Fault-Blanking Time
(MAX1541 Only)tFBLANK
FBLANK = REF356595
LDOON = VCC+150Thermal-Shutdown ThresholdTSHDNHysteresis = 10°CLDOON = GND+160°C
VCC Undervoltage-Lockout
ThresholdVUVLO(VCC)Rising edge, PWM disabled below this
level, hysteresis = 20mV4.14.254.4V
CURRENT LIMITILIM_ Adjustment Range0.252V
CSP_02.7Current-Limit Input RangeCSN_-0.3+28V
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear RegulatorDual Mode is a trademark of Maxim Integrated Products, Inc.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSValley Current-Limit Threshold
(Fixed)VLIM_ (VAL)VCSP_ - VCSN_, ILIM_ = VCC455055mV
VILIM_ = 250mV152535Valley Current-Limit Threshold
(Adjustable)VLIM_ (VAL)VCSP_ - VCSN_VILIM_ = 2.00V170200230mV
Current-Limit Threshold
(Negative)VNEGVCSP_ - VCSN _, SKIP = ILIM_ = VCC,
TA = +25°C-90-65-45mV
Current-Limit Threshold
(Zero Crossing)VZX
With respect to valley current-limit
threshold, VCSP_ - VCSN _, SKIP = GND,
ILIM_ = VCC
2.5mV
LSAT = VCC180200220
LSAT = open157175193Inductor-Saturation Current-Limit
Threshold
With respect to
valley current-
limit threshold,
ILIM_ = VCCLSAT = REF135150165
ILIM_ Saturation Fault Sink
CurrentIILIM_ (LSAT)VCSP - VCSN > inductor saturation current
limit, 0.25V < VILIM_ < 2.0V468µA
ILIM_ Leakage CurrentVCSP_ - VCSN _ < inductor saturation current
limit0.1µA
GATE DRIVERSDH_ Gate-Driver On-ResistanceRDHBST_-LX_ forced to 5V1.55Ω
DL_, high state1.55DL_ Gate-Driver On-ResistanceRDLDL_, low state0.63Ω
DH_ Gate-Driver Source/Sink
CurrentIDHDH_ forced to 2.5V, BST_-LX_ forced to 5V1A
DL_ Gate-Driver Source CurrentIDL
(SOURCE)DL_ forced to 2.5V1A
DL_ Gate-Driver Sink CurrentIDL (SINK)DL_ forced to 2.5V3A
DL_ rising35Dead TimetDEADDH_ rising26ns
INPUTS AND OUTPUTSOD On-ResistanceRODGATE = VCC1025Ω
OD Leakage CurrentGATE = GND, OD forced to 5.5V1200nA
Logic Input ThresholdON1, ON2, SKIP, GATE rising edge,
hysteresis = 225mV1.21.72.2V
LDOON Input Trip LevelRising edge, hysteresis = 250mV1.201.251.30V
Logic Input CurrentON1, ON2, LDOON, SKIP, GATE-1+1µA
High1.92.02.1
Dual Mode™ Threshold Voltage
FB1 ( M AX 1540A) ,
FB2 ( M AX 1540A/AX1541) Low0.050.10.15
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC= VDD= ON1 = ON2 = 5V, SKIP= GND, LDOIN (MAX1541) = V+, TA
= 0°C to +85°C, unless otherwise noted. Typicalvalues are at TA= +25°C.)
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC= VDD= ON1 = ON2 = 5V, SKIP= GND, LDOIN (MAX1541) = V+, TA
= 0°C to +85°C, unless otherwise noted. Typicalvalues are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSHighVCC -
0.4V
Open3.153.85
REF1.652.35
Four-Level Input Logic Levels
TON, OVP/UVP,
LSAT, SKIP,
FBLANK
Low0.5
Four-Level Logic Input CurrentTON, OVP/UVP, LSAT, SKIP, FBLANK
forced to GND or VCC-3+3µA
ELECTRICAL CHARACTERISTICS(V+ = 15V, VCC= VDD= ON1 = ON2 = 5V, SKIP= GND, LDOIN (MAX1541) = V+, TA
= -40°C to +85°C, unless otherwise noted.) (Note 4)
PARAMETERSYMBOLCONDITIONSMINMAXUNITS
INPUT SUPPLIES (Note 1)MAX1540A: battery voltage, V+ > VLDOOUT5.528VINMAX1541: battery voltage, V+ > VLDOOUT228
VBIASVCC, VDD (MAX1541)4.55.5Input Voltage Range
VLDOINMAX1541: LDO input supply,
VLDOIN > VLDOOUT4.528
FB1 and FB2 forced above the regulation
point, LSAT = GND1.5
Quiescent Supply Current (VCC)ICC
FB1 and FB2 forced above the regulation
point, ON1 or ON2 = VCC, VLSAT > 0.5V1.8
Quiescent Supply Current
(VDD, MAX1541 Only)IDDFB1 and FB2 forced above the regulation
point, ON1 or ON2 = VCC5µA
MAX1540A: FB1 and FB2 forced above the
regulation point, ON1 or ON2 = VCC,
VLDOON = V+ = 28V
Quiescent Supply Current (V+)IV+
MAX1541: ON1 or ON2 = VCC, VLDOON =
V+ = 28V40
Quiescent Supply Current
(LDOIN, MAX1541 Only)ILDOIN
FB1 and FB2 forced above the regulation
point, ON1 or ON2 = VCC,
VLDOON = V+ = 28V
110µA
Standby Supply Current (VDD)ON1 = ON2 = GND, VLDOON = V+ = 28V5µA
Standby Supply Current
(VDD, MAX1541 Only)ON1 = ON2 = GND, VLDOON = V+ = 28V5µA
MAX1540A: ON1 = ON2 = GND, LDOON =
V+ = 28V, VCC = 0 or 5V105
Standby Supply Current (V+)
MAX1541: ON1 = ON2 = GND, LDOON =
V+ = 28V, VCC = VDD = 0 or 5V5
Standby Supply CurrentON1 = ON2 = GND, VLDOON = V+ = 28V100µA
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC= VDD= ON1 = ON2 = 5V, SKIP= GND, LDOIN (MAX1541) = V+, TA
= -40°C to +85°C, unless otherwise noted.)(Note 4)
PARAMETERSYMBOLCONDITIONSMINMAXUNITSShutdown Supply Current (VCC)ON1 = ON2 = LDOON = GND5µA
Shutdown Supply Current
(VDD, MAX1541 Only)ON1 = ON2 = LDOON = GND5µA
MAX1540A: ON1 = ON2 = LDOON = GND,
V+ = 28V, VCC = 0 or 5V15
Shutdown Supply Current (V+)
MAX1541: ON1 = ON2 = LDOON = GND,
V+ = 28V, VCC = VDD = 0 or 5V5
Shutdown Supply Current
(LDOIN, MAX1541 Only)LDOON = GND10µA
PWM CONTROLLERSFB1 = GND1.7731.827
VOUT1
Preset output,
V+ = 5.5V to 28V,
SKIP = VCCFB1 = VCC1.1821.218MAX1540A Main Output-Voltage
Accuracy (OUT1) (Note 2)
VFB1Adjustable output, V+ = 5.5V to 28V,
SKIP = VCC0.6890.711
FB2 = GND2.4622.538
VOUT2
Preset output,
V+ = 5.5V to 28V,
SKIP = VCCFB2 = VCC1.4771.523MAX1540A Secondary Output-
Voltage Accuracy (OUT2)
(Note 2)
VFB2Adjustable output, V+ = 5.5V to 28V,
SKIP = VCC0.6890.711
REFIN1 = 0.35 x REF0.6890.711MAX1541 Main Feedback
Voltage Accuracy (FB1)VFB1V+ = 4.5V to 28V,
SKIP = VCCREFIN1 = REF1.972.03V
FB2 = GND2.4622.538
VOUT2
Preset output,
V+ = 4.5V to 28V,
SKIP = VCCFB2 = VCC1.7731.827MAX1541 Secondary Output-
Voltage Accuracy (OUT2)
(Note 2)VFB2Adjustable output, V+ = 4.5V to 28V,
SKIP = VCC0.6890.711
TON = G N D ( 620kH z) 149190
TON = RE F ( 485kH z) 191242
TON = op en ( 345kH z) 274335DH1 On-Time (Note 3)tON1V+ = 15V,
VOUT1 = 1.5V
TON = V CC ( 235kH z) 402491
TON = G N D ( 460kH z) 201256
TON = RE F ( 355kH z) 260331
TON = op en ( 255kH z) 371453DH2 On-Time (Note 3)tON2V+ = 15V,
VOUT2 = 1.5V
TON = V CC ( 170kH z) 556679
On-Time TrackingtON2 with respect to tON1 (Note 3)118152%
Minimum Off-TimetOFF(MIN)(Note 3)500ns
LINEAR REGULATOR (LDO) (Note 1)0 < ILDOOUT < 10mA4.855.10MAX1540A LDO Output-Voltage
AccuracyVLDOOUTON1 = ON2 = GND,
V+ = 6V to 28V0 < IL 100m A4.655.10V
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC= VDD= ON1 = ON2 = 5V, SKIP= GND, LDOIN (MAX1541) = V+, TA
= -40°C to +85°C, unless otherwise noted.)(Note 4)
PARAMETERSYMBOLCONDITIONSMINMAXUNITS0 < ILDOOUT < 10mA4.855.10MAX1541 LDO Output-Voltage
Accuracy (Fixed VLDOOUT)VLDOOUT
FBLDO = ON1 =
ON2 = GND,
VLDOIN = 6V to 28V0 < IL D OOU T < 100m A4.655.10
0 < ILDOOUT < 10mA1.2121.275MAX1541 LDO Feedback
Accuracy (Adjustable VLDOOUT)VFBLDO
FBLDO = LDOOUT,
ON1 = ON2 = GND,
VLDOIN = 4.5V to
28V0 < IL D OOU T < 100m A1.1751.275
MAX1540A: V+ - VLDOOUT, ILDOOUT = 50mA800
Dropout VoltageMAX1541: VLDOIN - VLDOOUT,
ILDOOUT = 50mA800mV
REFERENCE (REF)Reference VoltageVREFVCC = 4.5V to 5.5V, IREF = 01.982.02V
REFIN1 Input Bias CurrentIREFIN10.05µA
FAULT DETECTIONOvervoltage Trip ThresholdWith respect to error-comparator threshold,
OVP/UVP = VCC1021%
Output Undervoltage-Protection
Trip Threshold
With respect to error-comparator threshold,
OVP/UVP = VCC6476%
PGOOD_ Lower Trip ThresholdWith respect to error-comparator threshold,
hysteresis = 1%-14-5%
PGOOD_ Upper Trip ThresholdWith respect to error-comparator threshold,
hysteresis = 1%+5+14%
PGOOD_ Output Low VoltageISINK = 4mA0.3V
VCC Undervoltage-Lockout
ThresholdVUVLO(VCC)Rising edge, PWM disabled below this
level, hysteresis = 20mV4.14.4V
CURRENT LIMITCSP_02.7Current-Limit Input Range
CSN_-0.3+28.0
Valley Current-Limit Threshold
(Fixed)VLIM_ (VAL)VCSP_ - VCSN_, ILIM_ = VCC4060mV
Valley Current-Limit Threshold
(Adjustable)VLIM_ (VAL)VCSP_ - VCSN_, VILIM_ = 2.00V160240mV
INPUTS AND OUTPUTSLogic Input ThresholdON1, ON2, SKIP, GATE, rising edge,
hysteresis = 225mV1.22.2V
LDOON Input Trip LevelRising edge, hysteresis = 250mV1.21.3V
High1.92.1Dual Mode Threshold VoltageFB1 (MAX1540A),
FB2 (MAX1540A/MAX1541)Low0.050.15V
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC= VDD= ON1 = ON2 = 5V, SKIP= GND, LDOIN (MAX1541) = V+, TA
= -40°C to +85°C, unless otherwise noted.)(Note 4)
PARAMETERSYMBOLCONDITIONSMINMAXUNITSHighVCC -
0.4V
Open3.153.85
REF1.652.35
Four-Level Input Logic LevelsTON, OVP/UVP, LSAT, SKIP,
FBLANK
Low0.5
Note 1:For the MAX1540A, the gate-driver input supply (VDD) is internally connected to the fixed 5V linear-regulator output
(LDOOUT),
and the linear-regulator input supply (LDOIN) is internally connected to the battery voltage input (V+).
Note 2:When the inductor is in continuous conduction, the output voltage has a DC regulation level higher than the error-comparator
thresholdby 50% of the ripple. In discontinuous conduction (SKIP= GND, light load), the output voltage has a DC regulation
level higher than the trip level by approximately 1.5% due to slope compensation.
Note 3:On-time and off-time specifications are measured from 50% point to 50% point at the DH_ pin with LX_ = GND, VBST_ = 5V,
and a 250pF capacitor connected from DH_ to LX_. Actual in-circuit times may differ due to MOSFET switching speeds.
Note 4:Specifications to -40°C are guaranteed by design, not production tested.
OUT2 EFFICIENCY vs. LOAD CURRENT
(VOUT2 = 2.5V)MAX1540A toc01
LOAD CURRENT (A)
EFFICIENCY (%)0.1
SKIP = GND
SKIP = VCC
VIN = 7V
VIN = 12V
VIN = 20V
2.5V OUTPUT VOLTAGE (OUT2)
vs. LOAD CURRENTMAX1540A toc02
LOAD CURRENT (A)
OUTPUT VOLTAGE (V)321
SKIP = GND
SKIP = VCC
OUT1 EFFICIENCY vs. LOAD CURRENT
(VOUT1 = 1.0V)MAX1540A toc03
LOAD CURRENT (A)
EFFICIENCY (%)0.1
SKIP = GND
SKIP = VCC
VIN = 7V
VIN = 12V
VIN = 20V
Typical Operating Characteristics(MAX1541 circuit of Figure 12, VIN = 12V, VDD= VCC= 5V, SKIP= GND, TON = REF, TA = +25°C, unless otherwise noted.)
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
1.0V OUTPUT VOLTAGE (OUT1)
vs. LOAD CURRENTMAX1540A toc04
LOAD CURRENT (A)
OUTPUT VOLTAGE (V)312
SKIP = GND
SKIP = VCC
OUT2 SWITCHING FREQUENCY
vs. LOAD CURRENT
(VOUT2 = 2.5V)MAX1540A toc05
LOAD CURRENT (A)
SWITCHING FREQUENCY (kHz)321
SKIP = GND
SKIP = VCC
OUT1 SWITCHING FREQUENCY
vs. LOAD CURRENT
(VOUT1 = 1.0V)MAX1540A toc06
LOAD CURRENT (A)
SWITCHING FREQUENCY (kHz)321
SKIP = GND
SKIP = VCC
SWITCHING FREQUENCY
vs. INPUT VOLTAGEMAX1540A toc07
INPUT VOLTAGE (V)
SWITCHING FREQUENCY (kHz)20161284
4A LOAD
NO LOAD
2.5V OUTPUT
SKIP = VCC
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGEMAX1540A toc08
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (A)20121684
2.5V OUTPUT
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
(FORCED-PWM OPERATION)MAX1540A toc09
INPUT VOLTAGE (V)
SUPPLY CURRENT (mA)20161284
IBIAS
IIN
SKIP = ON1 = ON2 = VCC
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
(PULSE-SKIPPING OPERATION)MAX1540Atoc10
SUPPLY CURRENT (mA)16202448
IBIAS
SKIP = GND
ON1 = ON2 = VCC
2.0V REFERENCE LOAD REGULATIONMAX1540A toc11
REFERENCE VOLTAGE DEVIATION (mV)
REFERENCE DISTRIBUTION
MAX1540A toc12
SAMPLE PERCENTAGE (%)
SAMPLE SIZE = 50
Typical Operating Characteristics (continued)(MAX1541 circuit of Figure 12, VIN = 12V, VDD= VCC= 5V, SKIP= GND, TON = REF, TA = +25°C, unless otherwise noted.)
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
Typical Operating Characteristics (continued)(MAX1541 circuit of Figure 12, VIN = 12V, VDD= VCC= 5V, SKIP= GND, TON = REF, TA = +25°C, unless otherwise noted.)
LINEAR-REGULATOR OUTPUT (LDOOUT)
vs. LOAD CURRENTMAX1540A toc13
LDO LOAD CURRENT (mA)
LDO OUTPUT VOLTAGE (V)602040
VLDOIN = 5V
VLDOIN = 12V
STARTUP WAVEFORM
(HEAVY LOAD)MAX1540A toc14
3.3V
2.5V
400μs/div
A. ON2, 5V/div
B. INDUCTOR CURRENT,
2A/div
0.5Ω LOAD
C. OUT2, 2V/div
D. PGOOD2, 5V/div
STARTUP WAVEFORM
(LIGHT LOAD)MAX1540A toc15
3.3V
2.5V
200μs/div
A. ON2, 5V/div
B. INDUCTOR CURRENT,
2A/div
100Ω LOAD
C. OUT2, 2V/div
D. PGOOD2, 5V/div
SHUTDOWN WAVEFORM
(DISCHARGE MODE DISABLED)MAX1540A toc16
3.3V
10ms/div
2.5V
A. ON2, 5V/div
B. OUT2, 2V/div
C. INDUCTOR CURRENT,
2A/div
100Ω LOAD, OVP/UVP = REF OR GND
D. DL2, 5V/div
E. PGOOD2, 5V/div
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
Typical Operating Characteristics (continued)(MAX1541 circuit of Figure 12, VIN = 12V, VDD= VCC= 5V, SKIP= GND, TON = REF, TA = +25°C, unless otherwise noted.)
SHUTDOWN WAVEFORM
(DISCHARGE MODE ENABLED)MAX1540A toc17
3.3V
1ms/div
2.5V
A. ON2, 5V/div
B. OUT2, 2V/div
C. INDUCTOR CURRENT,
2A/div
100Ω LOAD, OVP/UVP = VCC OR OPEN
D. DL2, 5V/div
E. PGOOD2, 5V/div
2.5V OUTPUT LOAD TRANSIENT
(FORCED PWM)MAX1540A toc18
40μs/div
2.5V
2.4V
2.6V
A. IOUT2 = 0 TO 4A, 5A/div
B. VOUT2 = 2.5V, 100mV/div
SKIP = VCC
C. INDUCTOR CURRENT, 5A/div
D. LX2, 10V/div
12V
2.5V OUTPUT LOAD TRANSIENT
(PULSE SKIPPING)MAX1540A toc19
40μs/div
2.5V
2.4V
2.6V
A. IOUT2 = 0.1A TO 4A, 5A/div
B. VOUT2 = 2.5V, 100mV/div
SKIP = GND
C. INDUCTOR CURRENT, 5A/div
D. LX2, 10V/div
12V
LINEAR-REGULATOR
LOAD TRANSIENTMAX1540A toc20
100mA
100μs/div
3.3V
3.2V
3.4V
A. ILDOOUT = 1mA TO 100mA, 50mA/div
B. VLDOOUT = 3.3V, 100mV/div
SKIP = GND
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
Typical Operating Characteristics (continued)(MAX1541 circuit of Figure 12, VIN = 12V, VDD= VCC= 5V, SKIP= GND, TON = REF, TA = +25°C, unless otherwise noted.)
LINEAR-REGULATOR
LINE TRANSIENTMAX1540A toc21
20V
10V
20V
10V
3.8V
3.3V
2.8V
200μs/div
A. INPUT (VIN), 10V/div
B. LDOIN (10V TO 20V), 10V/div
C. LDOOUT (3.3V), 500mV/div
20mA LOAD
OUTPUT OVERLOAD
(UVP DISABLED)MAX1540A toc2220A
2.5V
10A
40μs/div
A. LOAD (0 TO 150mΩ), 10A/div
B. INDUCTOR CURRENT, 10A/div
OVP/UVP = OPEN OR GND
C. 2.5V OUTPUT, 2V/div
D. PGOOD2, 5V/div
OUTPUT OVERLOAD
(UVP ENABLED)MAX1540A toc2320A
2.5V
10A
20μs/div
A. LOAD (0 TO 150mΩ), 10A/div
B. INDUCTOR CURRENT, 10A/div
C. DL2, 5V/div
OVP/UVP = VCC OR REF
D. 2.5V OUTPUT, 2V/div
E. PGOOD2, 5V/div
INDUCTOR-SATURATION PROTECTION
(LSAT DISABLED)MAX1540A toc24
2.5VB
20μs/div
7.5A
A. IOUT2 = 0 TO 5A, 5A/div
B. 2.5V OUTPUT, 200mV/div
LSAT = GND, L = 3.3μH 3.5A
C. ILIM, 100mV/div
D. INDUCTOR CURRENT, 5A/div
0.67V
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
Typical Operating Characteristics (continued)(MAX1541 circuit of Figure 12, VIN = 12V, VDD= VCC= 5V, SKIP= GND, TON = REF, TA = +25°C, unless otherwise noted.)
INDUCTOR-SATURATION PROTECTION
(ΔVILIM = 200mV)MAX1540A toc25
2.5VB
20μs/div
7.5A
A. IOUT2 = 0 TO 5A, 5A/div
B. 2.5V OUTPUT, 200mV/div
LSAT = REF, L = 3.3μH 3.5A
C. ILIM, 200mV/div
D. INDUCTOR CURRENT, 5A/div
0.67V
0.47V
INDUCTOR-SATURATION PROTECTION
(ΔVILIM = 400mV)MAX1540A toc26
2.5V
1.5V
20μs/div
A. IOUT2 = 0 TO 5A, 5A/div
B. 2.5V OUTPUT, 1V/div
C. PGOOD, 5V/div
LSAT = REF, L = 3.3μH 3.5A
D. ILIM, 400mV/div
E. INDUCTOR CURRENT, 5A/div
0.67V
0.27V
MAX1541
DYNAMIC OUTPUT-VOLTAGE TRANSITION
(CREFIN1 = 100pF)MAX1540A toc27
-5A
1.5VB
40μs/div
A. GATE, 5V/div
B. OUT1 (1.0V TO 1.5V), 0.5V/div
C. REFIN1, 0.5V/div
200mA LOAD, SKIP = GND
D. PGOOD1, 5V/div
E. INDUCTOR CURRENT, 5A/div
1.5V
MAX1541
DYNAMIC OUTPUT-VOLTAGE TRANSITION
(CREFIN1 = 1nF)MAX1540A toc28
-5A
1.5VB
100μs/div
A. GATE, 5V/div
B. OUT1 (1.0V TO 1.5V), 0.5V/div
C. REFIN1, 0.5V/div
200mA LOAD, SKIP = GND
D. PGOOD1, 5V/div
E. INDUCTOR CURRENT, 5A/div
1.5V
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
PIN
MAX1540AMAX1541NAMEFUNCTION1OVP/UVP
Overvoltage/Undervoltage Protection and Discharge-Mode Control Input. This four-
level logic input selects between various output fault-protection options (Table 7) by
selectively enabling OVP protection and UVP protection. When enabled, the OVP limit
defaults at 116% of the nominal output voltage, and the UVP limit defaults at 70% of
the nominal output voltage. Discharge mode is enabled when OVP protection is also
enabled. Connect OVP/UVP to the following pins for the desired function:
VCC = enable OVP and discharge mode, enable UVP.
Open = enable OVP and discharge mode, disable UVP.
REF = disable OVP and discharge mode, enable UVP.
GND = disable OVP and discharge mode, disable UVP.
See the Fault Protection and (ON_) sections.SKIP
Pulse-Skipping Control Input. This four-level logic input enables or disables the light-
load pulse-skipping operation of each output:
VCC = OUT1 and OUT2 in forced-PWM mode.
Open = OUT1 in forced-PWM mode, OUT2 in pulse-skipping mode.
REF = OUT1 in pulse-skipping mode, OUT2 in forced-PWM mode.
GND = OUT1 and OUT2 in pulse-skipping mode.3LSAT
Inductor-Saturation Control Input. This four-level logic input sets the inductor-current
saturation limit as a multiple of the valley current-limit threshold set by ILIM, or
disables the function if not required. Connect LSAT to the following pins to set the
saturation current limit:
VCC = 2 x ILIM(VAL)
Open = 1.75 x ILIM(VAL)
REF = 1.5 x ILIM(VAL)
GND = disable LSAT protection
See the Inductor Saturation Limit and Setting the Current Limit sections.TON
On-Time Selection Control Input. This four-level logic input sets the K-factor value
used to determine the DH_ on-time (see the On-Time One-Shot (TON) section).
Connect to analog ground (GND), REF, or VCC; or leave TON unconnected to select
the following nominal switching frequencies:
VCC = 235kHz (OUT1) / 170kHz (OUT2)
Open = 345kHz (OUT1) / 255kHz (OUT2)
REF = 485kHz (OUT1) / 355kHz (OUT2)
GND = 620kHz (OUT1) / 460kHz (OUT2)VCC
Analog Supply Input. Connect to the system supply voltage (+4.5V to +5.5V) through
a series 20Ω resistor. Bypass VCC to analog ground with a 1µF or greater ceramic
capacitor.6GATE
Buffered N-Channel MOSFET Gate Input. A logic low on GATE turns off the internal
MOSFET so OD appears as high impedance. A logic high on GATE turns on the
internal MOSFET, pulling OD to ground.7CC1
Integrator Capacitor Connection for Controller 1. Connect a 47pF to 470pF (47pF typ)
capacitor from CC1 to analog ground (GND) to set the integration time constant for
the main MAX1541 controller (OUT1).
Pin Description
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
PIN
MAX1540AMAX1541NAMEFUNCTION8ILIM1
Valley Current-Limit Threshold Adjustment for Controller 1. The valley current-limit
threshold defaults to 50mV if ILIM1 is tied to VCC. In adjustable mode, the valley
current-limit threshold across CSP1 and CSN1 is precisely 1/10 the voltage seen at
ILIM1 over a 250mV to 2.5V range. The logic threshold for switchover to the 50mV
default value is approximately VCC - 1V. When the inductor-saturation protection
threshold is exceeded, ILIM1 sinks 6µA. See the Current-Limit Protection section.9ILIM2
Valley Current-Limit Threshold Adjustment for Controller 2. The valley current-limit
threshold defaults to 50mV if ILIM2 is tied to VCC. In adjustable mode, the valley
current-limit threshold across CSP2 and CSN2 is precisely 1/10th the voltage seen at
ILIM2 over a 250mV to 2.5V range. The logic threshold for switchover to the 50mV
default value is approximately VCC - 1V. When the inductor-saturation protection
threshold is exceeded, ILIM2 sinks 6µA. See the Current-Limit Protection section.10REF
2.0V Reference Voltage Output. Bypass REF to analog ground with a 0.1µF or greater
ceramic capacitor. The reference can source up to 50µA for external loads. Loading
REF degrades output voltage accuracy according to the REF load-regulation error.
The reference is disabled when the MAX1540A/MAX1541 are shut down.11REFIN1External Reference Input for Controller 1. REFIN1 sets the main feedback regulation
voltage (VFB1 = VREFIN1) of the MAX1541.12ODOpen-Drain Output. Controlled by GATE.13CSP2
Positive Current-Sense Input for Controller 2. Connect to the positive terminal of the
current-sense element. Figure 14 and Table 9 describe several current-sensing
options. The PWM controller does not begin a cycle unless the current sensed is less
than the valley current-limit threshold programmed at ILIM2.14CSN2
Negative Current-Sense Input for Controller 2. Connect to the negative terminal of the
current-sense element. Figure 14 and Table 9 describe several current-sensing
options. The PWM controller does not begin a cycle unless the current sensed is less
than the valley current-limit threshold programmed at ILIM2.15FB2
Feedback Input for Controller 2:AX 1540A: C onnect to V C C for a + 1.5V fi xed outp ut or to anal og g r ound ( G N D ) for a2.5V fi xed outp ut. For an ad j ustab l e outp ut ( 0.7V to 5.5V ) , connect FB2 to a r esi sti vei vi d er fr om OU T2. The FB2 r eg ul ati on l evel i s + 0.7V .AX 1541: C onnect to V C C for a + 1.8V fi xed outp ut or to anal og g r ound ( G N D ) for a2.5V fi xed outp ut. For an ad j ustab l e outp ut ( 0.7V to 5.5V ) , connect FB2 to a r esi sti vei vi d er fr om OU T2. The FB2 r eg ul ati on l evel i s + 0.7V .16OUT2
Output Voltage-Sense Connection for Controller 2. Connect directly to the positive
terminal of the output capacitors as shown in the standard application circuits
(Figures 1 and 12). OUT2 senses the output voltage to determine the on-time for the
high-side switching MOSFET. OUT2 also serves as the feedback input when using
the preset internal output voltages as shown in Figure 10. When discharge mode is
enabled by OVP/UVP, the output capacitor is discharged through an internal 10Ω
resistor connected between OUT2 and ground.
Pin Description (continued)
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
PIN
MAX1540AMAX1541NAMEFUNCTION17PGOOD2
Open-Drain Power-Good Output. PGOOD2 is low when the output voltage is more
than 10% (typ) above or below the normal regulation point, during soft-start, and in
shutdown. After the soft-start circuit has terminated, PGOOD2 becomes high
impedance if the output is in regulation.18DH2High-Side Gate-Driver Output for Controller 2. DH2 swings from LX2 to BST2.19LX2Inductor Connection for Controller 2. Connect to the switched side of the inductor.
LX2 serves as the lower supply rail for the DH2 high-side gate driver.20BST2
Boost Flying-Capacitor Connection for Controller 2. Connect to an external capacitor
and diode as shown in Figure 8. An optional resistor in series with BST2 allows the
DH2 pullup current to be adjusted.21GNDAnalog and Power Ground. Connect backside pad to GND.22DL2Low-Side Gate-Driver Output for Controller 2. DL2 swings from GND to LDOOUT
(MAX1540A) or GND to VDD (MAX1541).23V+
Battery Voltage Input. The controller uses V+ to set the on-time one-shot timing. The
DH on-time is inversely proportional to input voltage over a range of 2V to 28V. For
the MAX1540A, V+ also serves as the linear-regulator input supply.24LDOIN
Internal Linear-Regulator Input Supply. Power LDOIN from a 4.5V to 28V voltage
source. Bypass LDOIN to GND with a 4.7µF or greater capacitor. For the MAX1540A,
LDOIN is internally connected to V+. For the MAX1541, LDOIN must be connected to
VDD when LDO is not used.
—25VDD
MAX1541 Supply Voltage Input for the DL_ Gate Driver. Connect to the system
supply voltage (+4.5V to +5.5V). Bypass VDD to power ground with a 1µF or greater
ceramic capacitor. For the MAX1540A, LDOOUT supplies the DL_ gate drivers
(VDD = LDOOUT).26LDOOUT
Linear Regulator Output. Bypass LDOOUT with a 1µF or greater capacitor per 5mA of
load (internal and external), with a minimum of 4.7µF. For the MAX1540A, LDOOUT
powers the DL_ gate drivers (VDD internally connected to LDOOUT).27FBLDO
Feedback Input for the Linear Regulator. Connect to GND for a fixed 5V output. For
an adjustable output (1.25V to VLDOIN - 0.6V), connect FBLDO to a resistive voltage-
divider from LDOOUT to analog ground (GND). The FBLDO regulation voltage is
+1.25V. For the MAX1540A, FBLDO is internally connected to GND for a fixed 5V
output.28DL1Low-Side Gate-Driver Output for Controller 1. DL1 swings from GND to LDOOUT
(MAX1540A) or GND to VDD (MAX1541).29LDOONLinear-Regulator Enable Input. For automatic startup, connect to V+ or LDOIN
(MAX1541). Connect to GND to shut down the linear regulator.30BST1
Boost Flying-Capacitor Connection for Controller 1. Connect to an external capacitor
and diode as shown in Figure 8. An optional resistor in series with BST1 allows the
DH1 pullup current to be adjusted.
Pin Description (continued)
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
PIN
MAX1540AMAX1541NAMEFUNCTION31LX1Inductor Connection for Controller 1. Connect to the switched side of the inductor.
LX1 serves as the lower supply rail for the DH1 high-side gate driver.32DH1High-Side Gate-Driver Output for Controller 1. DH1 swings from LX1 to BST1.33PGOOD1
Open-Drain Power-Good Output. PGOOD1 is low when the output voltage is more
than 10% (typ) above or below the normal regulation point, during soft-start, and in
shutdown. After the soft-start circuit has terminated, PGOOD1 becomes high
impedance if the output is in regulation. For the MAX1541, PGOOD1 is
blanked—forced high-impedance state—when FBLANK is enabled and the controller
detects a transition on GATE.34OUT1
Output Voltage-Sense Connection for Controller 1. Connect directly to the positive
terminal of the output capacitors as shown in the standard application circuits
(Figures 1 and 12). OUT1 senses the output voltage to determine the on-time for the
high-side switching MOSFET. For the MAX1540A, OUT1 also serves as the feedback
input when using the preset internal output voltages as shown in Figure 10. When
discharge mode is enabled by OVP/UVP, the output capacitor is discharged throughl10ΩittdbtOUT1dd35FB1
Feedback Input for Controller 1:AX 1540A: C onnect to V C C for a + 1.2V fi xed outp ut or to anal og g r ound ( G N D ) for a1.8V fi xed outp ut. For an ad j ustab l e outp ut ( 0.7V to 5.5V ) , connect FB1 to a r esi sti vei vi d er fr om OU T1. The FB1 r eg ul ati on l evel i s + 0.7V .AX 1541: The FB1 r eg ul ati on l evel i s set b y the vol tag e at RE FIN 1.36CSN1
Negative Current-Sense Input for Controller 1. Connect to the negative terminal of the
current-sense element. Figure 14 and Table 9 describe several current-sensing
options. The PWM controller does not begin a cycle unless the current sensed is less
than the valley current-limit threshold programmed at ILIM1.37CSP1
Positive Current-Sense Input for Controller 1. Connect to the positive terminal of the
current-sense element. Figure 14 and Table 9 describe several current-sensing
options. The PWM controller does not begin a cycle unless the current sensed is less
than the valley current-limit threshold programmed at ILIM1.38FBLANK
Fault-Blanking Control Input. This four-level logic input enables or disables fault
blanking, and sets the forced-PWM operation time (tFBLANK). When fault blanking is
enabled, PGOOD1 and the OVP/UVP protection for controller 1 are blanked for the
selected time period after the MAX1541 detects a transition on GATE. Additionally,
controller 1 enters forced-PWM mode for the duration of tFBLANK anytime GATE
changes states. Connect FBLANK as follows:
VCC = 220µs tFBLANK, fault blanking enabled.
Open = 140µs tFBLANK, fault blanking enabled.
REF = 65µs tFBLANK, fault blanking enabled.
GND = 140µs tFBLANK, fault blanking disabled.
See the Electrical Characteristics table for the tFBLANK limits.
Pin Description (continued)
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
PIN
MAX1540AMAX1541NAMEFUNCTION39ON2
OUT2 Enable Input. Pull ON2 to GND to shut down controller 2 (OUT2). Connect to
VCC for normal operation. When discharge mode is enabled by OVP/UVP, the output
is discharged through a 10Ω resistor between OUT2 and GND, and DL2 is forced
high after VOUT2 drops below 0.3V. When discharge mode is disabled by OVP/UVP,
OUT2 remains a high-impedance input and DL2 is forced low so LX2 also appears as
a high impedance. A rising edge on ON1 or ON2 clears the fault-protection latch.40ON1
OUT1 Enable Input. Pull ON1 to GND to shut down controller 1 (OUT1). Connect to
VCC for normal operation. When discharge mode is enabled by OVP/UVP, the output
is discharged through a 10Ω resistor between OUT1 and GND, and DL1 is forced
high after VOUT1 drops below 0.3V. When discharge mode is disabled by OVP/UVP,
OUT1 remains a high-impedance input and DL1 is forced low so LX1 also appears as
high impedance. A rising edge on ON1 or ON2 clears the fault-protection latch.—EPExposed Backside Pad. Connect the exposed backside pad to analog ground.
Pin Description (continued)
Table 1. Component Selection for Standard Applications
MAX1540AMAX1541COMPONENT
PWM1PWM2PWM1PWM2Input Voltage (VIN)7V to 24V7V to 24V7V to 24V7V to 24V
Output Voltage (VOUT_)1.8V2.5V1.0V/1.5V2.5V
Load Current (IOUT_)4A8A4A4Aw i tchi ng Fr eq uencyfS W_) TON = REF (485kHz)TON = REF (355kHz)TON = REF (485kHz)TON = REF (355kHz)
Input Capacitor (CIN)(2) 10µF, 25V
Taiyo Yuden TMK432BJ106KM
(2) 4.7µF, 25V
Taiyo Yuden TMK325BJ475KM
Output Capacitor
(COUT_)
220µF, 6.3V, 12mΩ
Sanyo POSCAP
6TPD220M
330µF, 4V, 12mΩ
Sanyo POSCAP
4TPD330M
470µF, 4V, 10mΩ
Sanyo POSCAP
4TPD470M
220µF, 6.3V, 12mΩ
Sanyo POSCAP
6TPD220M
High-Side MOSFET
(NH_)
35mΩ, 30V
Fairchild 1/2 FDS6982S
20mΩ, 30V
Fairchild FDS6690
35mΩ, 30V
Fairchild 1/2 FDS6982S
35mΩ, 30V
Fairchild 1/2 FDS6982S
Low-Side MOSFET
(NL_)
22mΩ, 30V
Fairchild 1/2 FDS6982S
12.5mΩ, 30V
Fairchild FDS6670S
22mΩ, 30V
Fairchild 1/2 FDS6982S
22mΩ, 30V
Fairchild 1/2 FDS6982S
Low-Side Schottky
(DL_)
(if needed)
1A, 30V Schottky
Nihon EP10QS03L
1A, 30V Schottky
Nihon EP10QS03L
1A, 30V Schottky
Nihon EP10QS03L
1A, 30V Schottky
Nihon EP10QS03L
Inductor (L_)
2.5µH, 6.2A, 15mΩ
Sumida
CDEP105(H)-2R5
2.2µH, 10A, 4.4mΩ
Sumida
CDEP105(L)-2R2
1.8µH, 9.0A, 6.2mΩ
Sumida
CDEP105(S)-1R8
4.3µH, 6.8A, 8.7mΩ
Sumida
CDEP105(L)-4R3
RSENSE_
15mΩ ±1%, 0.5W
IRC LR2010-01-R015F
or Dale WSL-2010-R015F
5mΩ ±1%, 0.5W
IRC LR2010-01-R005F
or Dale WSL-2010-R005F
15mΩ ±1%, 0.5W
IRC LR2010-01-R015F
or Dale WSL-2010-R015F
15mΩ ±1%, 0.5W
IRC LR2010-01-R015F
or Dale WSL-2010-R015F
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear RegulatorMAX1540A
+5V BIAS
SUPPLY
OUTPUT 1
1.8V, 4A (MAX)
REF
(485kHz/355kHz)
POWER GROUND
ANALOG GROUND
POWER-GOOD
OFF
OPEN (ILIM(VAL) x 1.75)
OUTPUT 2
2.5V, 8A (MAX)
INPUT (VIN)*
7V TO 20V
LDOOUT
DH1
BST1
LX1
CSP1
DL1
CSN1
OUT1
FB1
SKIP
TON
REF
ILIM1
ILIM2PGOOD2
PGOOD1
VCC
ON2
ON1
LDOON
LSAT
OVP/UVP
FB2
OUT2
CSN2
CSP2
GND
DL2
LX2
BST2
DH2
100kΩR6
100kΩ
1μF
20Ω
COUT2
330μF
RCS2
5mΩ
2.2μH
DL2DL1
RCS1
15mΩ
COUT1
220μF
2.5μH
NL1NL2
NH1NH2
CBST2
0.1μF
CBST1
0.1μF
DBSTDBST
22μF
CREF
0.22μF
470pF
470pF
100kΩ
49.9kΩ
200kΩ
49.9kΩ
SEE TABLE 1 FOR COMPONENT SPECIFICATIONS.
*LOWER INPUT VOLTAGES REQUIRE
ADDITIONAL INPUT CAPACITANCE.
+5V BIAS
SUPPLY
CIN
(2) 10μF
MAX1540A/MAX1541
Standard Application CircuitsThe MAX1540A standard application circuit (Figure 1)
generates a 1.8V and 2.5V rail for general-purpose use
in a notebook computer. The MAX1541 Standard
Application Circuit (Figure 12) generates a dynamically
adjustable output voltage (OUT1), typical of a graphics-
processor core requirement, and a fixed 2.5V output
(OUT2).
See Table 1 for component selections. Table 2 lists the
component manufacturers.
Detailed DescriptionThe MAX1540A/MAX1541 provide three independent out-
puts with independent enable controls. They contain two
Quick-PWM step-down controllers ideal for low-voltage
power supplies for notebook computers, and a 100mA
linear regulator. Maxim’s proprietary Quick-PWM pulse-
width modulators in the MAX1540A/ MAX1541 are specifi-
cally designed for handling fast load steps while
maintaining a relatively constant operating frequency and
inductor operating point over a wide range of input volt-
ages. The Quick-PWM architecture circumvents the poor
load-transient timing problems of fixed-frequency current-
mode PWMs, while also avoiding the problems caused
by widely varying switching frequencies in conventional
constant-on-time and constant-off-time PWM schemes.
The MAX1540A linear regulator draws power from the
battery voltage and generates a preset 5V, which can
be used to bootstrap the buck controllers for automatic
startup. The MAX1541’s linear regulator can be con-
nected to any input source from 4.5V to 28V to gener-
ate an adjustable output voltage as low as 1.25V, or as
high as the input source with 800mV of dropout at
50mA load.
Single-stage buck conversion allows the MAX1540A/
MAX1541 to directly step down high-voltage batteries
for the highest possible efficiency. Alternatively, two-
stage conversion (stepping down from another system
supply rail instead of the battery at a higher switching
frequency) allows the minimum possible physical size.
The MAX1540A generates chipset, dynamic random-
access memory (DRAM), CPU I/O, or other low-voltage
supplies down to 0.7V. The MAX1541 powers chipsets
and graphics processor cores that require dynamically
adjustable output voltages, or generates the active ter-
mination bus that must track the input reference. The
MAX1540A is available in a 32-pin thin QFN package
with optional inductor-saturation protection and over-
voltage/undervoltage protection. The MAX1541 is avail-
able in a 40-pin thin QFN package with optional
inductor-saturation protection and overvoltage/under-
voltage protection.
+5V Bias Supply (VCCand VDD)The MAX1540A/MAX1541 require a 5V bias supply in
addition to the battery. This 5V bias supply is either the
MAX1540A/MAX1541s’ internal linear regulator or the
notebook’s 95%-efficient 5V system supply. Keeping the
bias supply external to the IC can improve efficiency
and allows the fixed 5V or adjustable linear regulator
(MAX1541) to be used for other applications. For the
MAX1540A, the gate-driver input supply (VDD) is con-
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
Table 2. Component Suppliers
SUPPLIERPHONEWEBSITECentral
Semiconductor
(USA)www.centralsemi.com
Coilcraft800-322-2645
(USA)www.coilcraft.com
Fairchild
Semiconductor
(USA)www.fairchildsemi.com
International
Rectifier
(USA)www.irf.com
Kemet408-986-0424
(USA)www.kemet.com
Panasonic
(Singapore),
(USA)
www.panasonic.com
Sanyo619-661-6835
(USA)www.sanyovideo.com
Siliconix
(Vishay)
(USA)www.vishay.com
Sumida408-982-9660
(USA)www.sumida.com
Taiyo Yuden
(Japan),
(USA)
www.t-yuden.com
TDK
(USA),
(Japan)
www.component.tdk.com
TOKO858-675-8013
(USA)www.tokoam.com
nected internally to the fixed 5V linear-regulator output
(LDOOUT).
The 5V bias supply must provide VCC(PWM controller)
and VDD(gate-drive power), so the maximum current
drawn is:
IBIAS= ICC+ fSW(QG(LOW)+ QG(HIGH)) 4mA to 50mA (typ)
where ICCis 1.1mA (typ), fSWis the switching frequency,
and QG(LOW)and QG(HIGH)are the MOSFET data
sheet’s total gate-charge specification limits at VGS= 5V.
The V+ battery input and 5V bias inputs (VCCand VDD)
can be connected together if the input source is a fixed
4.5V to 5.5V supply. If the 5V bias supply powers up
prior to the battery supply, the enable signals (ON1 and
ON2 going from low to high) must be delayed until the
battery voltage is present in order to ensure startup.
Free-Running, Constant On-Time, PWM
Controller with Input Feed ForwardThe Quick-PWM control architecture is a pseudofixed-
frequency, constant on-time, current-mode regulator
with voltage feed forward (Figure 2). This architecture
relies on the output filter capacitor’s ESR to act as a
current-sense resistor, so the output ripple voltage pro-
vides the PWM ramp signal. The Quick-PWM algorithm
is simple: the high-side switch on-time relies solely on
an adjustable one-shot whose pulse width is inversely
proportional to input voltage and directly proportional to
output voltage. Another one-shot sets a fixed minimum
off-time (400ns typ). The controller triggers the on-time
one-shot when the error comparator is low, the inductor
current is below the valley current-limit threshold, and
the minimum off-time one-shot has timed out.
On-Time One-Shot (TON)The heart of the PWM core is the one-shot that sets the
high-side switch on-time. This fast, low-jitter, adjustable
one-shot includes circuitry that varies the on-time in
response to the battery and output voltages. The high-
side switch on-time is inversely proportional to the bat-
tery voltage as measured by the V+ input (VIN= V+),
and proportional to the output voltage as measured by
the OUT_ input:
where K (switching period) is set by the TON pin-strap
connection (Table 3). This algorithm results in a nearly
constant switching frequency despite the lack of a fixed-
frequency clock generator. The benefits of a constant
switching frequency are twofold: 1) the frequency can
be selected to avoid noise-sensitive regions such as the
455kHz IF band and 2) the inductor ripple-current oper-
ating point remains relatively constant, resulting in easy
design methodology and predictable output voltage rip-
ple. The on-time for the main controller (DH1) is set 15%
higher than the nominal frequency setting (200kHz,
300kHz, 420kHz, or 540kHz), while the on-time for the
secondary controller (DH2) is set 15% lower than the
nominal setting. This prevents audio-frequency “beat-
ing” between the two asynchronous regulators.
The on-time one-shot has good accuracy at the operat-
ing points specified in the Electrical Characteristics
(approximately ±12.5% at 540kHz and 420kHz nominal
settings, and ±10% with the 300kHz and 200kHz set-
tings). On-times at operating points far removed from
the conditions specified in the Electrical Characteristics
can vary over a wider range.
The constant on-time translates only roughly to a constant
switching frequency. The on-times guaranteed in the
Electrical Characteristicsare influenced by resistive loss-
es and by switching delays in the high-side MOSFET.
Resistive losses—including the inductor, both MOSFETs,
and PC board copper losses in the output and ground—
tend to raise the switching frequency as the load increas-
es. The dead-time effect increases the effective on-time,
reducing the switching frequency as one or both dead
times add to the effective on-time. It occurs only in PWM
mode (SKIP= VCC) and during dynamic output-voltage
transitions when the inductor current reverses at light- or
negative-load currents. With reversed inductor current,
the inductor’s EMF causes LX_ to go high earlier than
normal, extending the on-time by a period equal to the
driver dead time.
For loads above the critical conduction point, where the
dead-time effect no longer occurs, the actual switching
frequency is:
where VDROP1is the sum of the parasitic voltage drops
in the inductor discharge path, including synchronous
rectifier, inductor, and PC board resistances; VDROP2is
the sum of the resistances in the charging path, includ-
fSWOUT_DROP1INDROP1DROP2V+V-V=()
On-TimeV
OUT=⎛⎜⎞⎟K
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear RegulatorVALLEY
CURRENT
LIMIT
ZERO
CROSSING
SATURATION
LIMIT
VALLEY
CURRENT
LIMIT
ZERO
CROSSING
SATURATION
LIMIT
*V+
TON
SKIP
ILIM1
CSP1
CSN1
BST1
DH1
LX1
*VDD
DL1
**CC1
GND
LSAT
ILIM2
CSP2
CSN2
BST2
DH2
LX2
*VDD
VCC
DL2
GND
REF
13R0.7V7R
CURRENT
LIMIT 1
(FIGURE 5)
CURRENT
LIMIT 2
(FIGURE 5)
PWM
CONTROLLER 1
(FIGURE 3)
PWM
CONTROLLER 2
(FIGURE 3)
FB1 DECODE
(FIGURE 10)
POWER-GOOD AND
FAULT PROTECTION 1
(FIGURE 9)
FB2 DECODE
(FIGURE 10)
INTERNAL
MAX1540A/MAX1541
OPTION
POWER-GOOD AND
FAULT PROTECTION 2
(FIGURE 9)
FB1
**REFIN1
OUT1
ON1
PGOOD1
FB2
OUT2
2.0V
REF
ON2
PGOOD2
FAULT1
INT REF1INT FB1INT FB2
FAULT2
QUAD-LEVEL
DECODE
QUAD-LEVEL
DECODE AND
TIMER
**FBLANK
**OD
OVP/UVPBLANK
ENABLE OVP
ENABLE UVP
LINEAR REGULATOR
(FIGURE 13)
*LDOIN
*LDOOUT
**FBLDO
LDOON
**GATE
MAX1541
CONTROLLER 1
ONLY
MAX1540A/MAX1541
INT REF2
*FOR THE MAX1540A:
LDOIN IS CONNECTED TO V+.
LDOOUT IS CONNECTED TO VDD.
**MAX1541 CONTROLLER ONLY.
ing the high-side switch, inductor, and PC board resis-
tances; and tONis the on-time calculated by the
MAX1540A/MAX1541.
Light-Load Operation (SKIP)The four-level SKIPinput selects light-load, pulse-skip-
ping operation by independently enabling or disabling
the zero-crossing comparator for each controller (Table
4). When the zero-crossing comparator is enabled, the
controller forces DL_ low when the current-sense inputs
detect zero inductor current. This keeps the inductor
from discharging the output capacitors and forces the
controller to skip pulses under light-load conditions to
avoid overcharging the output. When the zero-crossing
comparator is disabled, the controller maintains PWM
operation under light-load conditions (see the Forced-
PWM Modesection).
Automatic Pulse-Skipping ModeIn skip mode, an inherent automatic switchover to PFM
takes place at light loads (Figure 3). This switchover is
affected by a comparator that truncates the low-side
switch on-time at the inductor current’s zero crossing.
The zero-crossing comparator differentially senses the
inductor current across the current-sense inputs (CSP_
to CSN_). Once VCSP_- VCSN_drops below 5% of the
current-limit threshold (2.5mV for the default 50mV cur-
rent-limit threshold), the comparator forces DL_ low
(Figure 3). This mechanism causes the threshold
between pulse-skipping PFM and nonskipping PWM
tinuous and discontinuous inductor-current operation
(also known as the “critical-conduction” point). The
load-current level at which PFM/PWM crossover
occurs, ILOAD(SKIP), is equal to half the peak-to-peak
ripple current, which is a function of the inductor value
(Figure 4). This threshold is relatively constant, with
only a minor dependence on battery voltage:
where K is the on-time scale factor (Table 3). For exam-
ple, in the MAX1541 Standard Application Circuit
(Figure 12) (K = 3.0µs, VOUT2= 2.5V, VIN= 12V, and L
= 4.3µH), the pulse-skipping switchover occurs at:
The crossover point occurs at an even lower value if a
swinging (soft-saturation) inductor is used. The switch-
ing waveforms may appear noisy and asynchronous
when light loading causes pulse-skipping operation,
but this is a normal operating condition that results in
high light-load efficiency. Trade-offs in PFM noise vs.
light-load efficiency are made by varying the inductor
value. Generally, low inductor values produce a broad-
er efficiency vs. load curve, while higher values result in
higher full-load efficiency (assuming that the coil resis-
tance remains fixed) and less output voltage ripple.
Penalties for using higher inductor values include larger
physical size and degraded load-transient response
(especially at low input-voltage levels).
DC-output accuracy specifications refer to the thresh-
old of the error comparator. When the inductor is in
continuous conduction, the MAX1540A/MAX1541 regu-
late the valley of the output ripple, so the actual DC out-
put voltage is higher than the trip level by 50% of the
output ripple voltage. In discontinuous conduction..2.5V3s4.3H
12V-2.5V
12V⎜⎞⎟⎛⎜⎞⎟=0069μA
ILOAD(SKIP)OUTINOUTV≈⎛⎜⎞⎟⎛⎜⎞⎟
MAX1540A/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
Table 3. Approximate K-Factor Errors
CONTROLLER 1 (OUT1)CONTROLLER 2 (OUT2)
NOMINAL TON
SETTING (kHz)
K-FACTOR
ERROR (%)
TYPICAL
K-FACTOR
(µs)
MINIMUM VIN AT
VOUT1 = 1.8V*
(V)
TYPICAL
K-FACTOR
(µs)
MINIMUM VIN AT
VOUT2 = 2.5V*
(V)200kHz (TON = VCC)±104.5 (235kHz)2.286.2 (170kHz)2.96
300kHz (TON = open)±103.0 (345kHz)2.524.1 (255kHz)3.18
420kHz (TON = REF)±12.52.2 (485kHz)2.913.0 (355kHz)3.48
540kHz (TON = GND)±12.51.7 (620kHz)3.422.3 (460kHz)3.87
*See the Step-Down Converter Dropout Performance section (h = 1.5 and worst-case K-factor value used).
Table 4. SKIPConfiguration TableSKIP
OUT1 MODEOUT2 MODEVCCForced PWMForced PWM
OpenForced PWMPulse skipping
REFPulse skippingForced PWM
GNDPulse skippingPulse skipping
