MAX1992ETG ,Quick-PWM Step-Down Controllers with Inductor Saturation Protection and Dynamic Output VoltagesFeaturesThe MAX1992/MAX1993 pulse-width modulation (PWM)♦ Inductor Saturation Protectioncontrollers ..
MAX1992ETG+ ,Quick-PWM Step-Down Controllers with Inductor Saturation Protection and Dynamic Output VoltagesELECTRICAL CHARACTERISTICS(V+ = 15V, V = V = SHDN = 5V, SKIP = GND, T = 0°C to +85°C, unless otherw ..
MAX1992ETG+T ,Quick-PWM Step-Down Controllers with Inductor Saturation Protection and Dynamic Output VoltagesApplications18 17 16 15 14 13Notebook Computers VDD 19 CSN1220 11 CSPPGNDCore/IO Supplies as Low as ..
MAX1993ETG ,Quick-PWM Step-Down Controllers with Inductor Saturation Protection and Dynamic Output VoltagesMAX1992/MAX199319-2661; Rev 0; 10/02Quick-PWM Step-Down Controllers with InductorSaturation Protect ..
MAX1993ETG+ ,Quick-PWM Step-Down Controllers with Inductor Saturation Protection and Dynamic Output VoltagesMAX1992/MAX199319-2661; Rev 1; 9/05Quick-PWM Step-Down Controllers with InductorSaturation Protecti ..
MAX1993ETG+T ,Quick-PWM Step-Down Controllers with Inductor Saturation Protection and Dynamic Output VoltagesFeaturesThe MAX1992/MAX1993 pulse-width modulation (PWM)♦ Inductor Saturation Protectioncontrollers ..
MAX5026EUT-T ,500kHz / 36V Output / SOT23 / PWM Step-Up DC-DC ConvertersApplications Small, 6-Pin SOT23 PackageTV Tuner Power SupplyLow-Noise Varactor Diode BiasingOrderi ..
MAX5026EUT-T ,500kHz / 36V Output / SOT23 / PWM Step-Up DC-DC ConvertersFeaturesThe MAX5025–MAX5028 constant-frequency, pulse- Input Voltage Range:width modulating (PWM), ..
MAX502ACNG+ ,Voltage-Output, 12-Bit Multiplying DACsFeatures
. 12-Blt Voltage Output DAC
. i10V and SmA Output Drive
. Monotonic Over Temperat ..
MAX502ACWG+T ,Voltage-Output, 12-Bit Multiplying DACsApplications
Digital Attenuators
Gain Amplifiers
Digital to 4mA-to-20mA Converters
Automatic ..
MAX502AEWG+ ,Voltage-Output, 12-Bit Multiplying DACsELECTRICAL CHARACTERISTICS
Dual Supply (VDD = +11.4V to +15.75V, Vss = -11.4V to -15.75V, VREF = ..
MAX502AEWG+T ,Voltage-Output, 12-Bit Multiplying DACsGeneral Description
The MAX501/MAX502 are 12-bit, 4-quadrant, voltage-
output, multiplying digi ..
MAX1992ETG
Quick-PWM Step-Down Controllers with Inductor Saturation Protection and Dynamic Output Voltages
General DescriptionThe MAX1992/MAX1993 pulse-width modulation (PWM)
controllers provide high-efficiency, excellent transient
response, and high DC output accuracy. The devices
step down high-voltage batteries to generate low-
voltage CPU core or chipset/RAM supplies in notebook
computers.
Maxim’s proprietary Quick-PWM™ quick-response, con-
stant on-time PWM control scheme handles wide
input/output voltage ratios with ease and provides 100ns
“instant-on” response to load transients, while maintaining
a relatively constant switching frequency. Efficiency is
enhanced by the ability to drive very large synchronous-
rectifier MOSFETs. Current sensing to ensure reliable
overload and inductor saturation protection is available
using an external current-sense resistor in series with the
output. Alternatively, the controller can sense the current
across the synchronous rectifier alone or use lossless
inductor sensing for lowest power dissipation.
Single-stage buck conversion allows the MAX1992/
MAX1993 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 the maximum switching fre-
quency allows the minimum possible physical size.
The MAX1992 powers the CPU core, chipset, DRAM, or
other supply rails as low as 0.7V. The MAX1993 powers
chipsets and graphics processor cores, which require
dynamically adjustable output voltages. The MAX1993
provides a tracking input that can be used for active ter-
mination buses. The MAX1992/MAX1993 are available in
a 24-pin thin QFN package with optional overvoltage and
undervoltage protection.
For dual step-down PWM controllers with inductor satu-
ration protection, external reference input voltage, and
dynamically selectable output voltages, refer to the
MAX1540/MAX1541 data sheet.
ApplicationsNotebook Computers
Core/IO Supplies as Low as 0.7V
1.8V and 2.5V Supplies
DDR Memory Termination (MAX1993)
Active Termination Buses (MAX1993)
CPU/Chipset/GPU with Dynamic Voltage Cores
(MAX1993)
FeaturesInductor Saturation ProtectionAccurate Current LimitUltra-High EfficiencyQuick-PWM with 100ns Load-Step ResponseMAX1992
1.8V/2.5V Fixed or 0.7V to 5.5V Adjustable
Output RangeMAX1993
External Reference Input
Dynamically Selectable Output Voltage
(0.7V to 5.5V)
Optional Power-Good and Fault Blanking
During Transitions±1% VOUTAccuracy Over Line and Load2V to 28V Battery Input Range (VIN)200/300/450/600kHz Switching FrequencyOvervoltage/Undervoltage Protection Option1.7ms Digital Soft-StartDrives Large Synchronous Rectifier FETs2V ±0.7% Reference OutputPower-Good Window Comparator
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages17161514345
THIN QFN
4mm x 4mmTOP VIEW
MAX1992
CSNVDD
PGND
AGND
VCC
SHDNOVP/UVP
CSP
N.C.N.C
OUT
ILIM
PGOOD
REF
LSAT
N.C.TONBSTLXDHV+
SKIP
A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES.
Pin Configurations19-2661; Rev 1; 9/05
Quick-PWM is a trademark of Maxim Integrated Products, Inc.
Ordering Information
PARTTEMP RANGEPIN-PACKAGE
MAX1992ETG-40°C to +85°C24 Thin QFN 4mm × 4mm
MAX1992ETG+-40°C to +85°C24 Thin QFN 4mm × 4mm
MAX1993ETG-40°C to +85°C24 Thin QFN 4mm × 4mm
MAX1993ETG+-40°C to +85°C24 Thin QFN 4mm × 4mm
Pin Configurations continued at end of data sheet.
+ Denotes lead-free package.
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
ABSOLUTE MAXIMUM RATINGS (Note 1)
ELECTRICAL CHARACTERISTICS(V+ = 15V, VCC = VDD = SHDN= 5V, SKIP= GND, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
Stresses 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.
V+ to AGND............................................................-0.3V to +30V
VCCto AGND............................................................-0.3V to +6V
VDDto PGND............................................................-0.3V to +6V
PGOOD, ILIM, SKIP, SHDNto AGND......................-0.3V to +6V
REFIN, FB, CSP to AGND.........................................-0.3V to +6V
GATE, OD to GND (MAX1993 only).........................-0.3V to +6V
TON, OVP/UVP, LSAT to AGND.................-0.3V to (VCC+ 0.3V)
REF, OUT to AGND....................................-0.3V to (VCC+ 0.3V)
FBLANK to GND (MAX1993 only)..............-0.3V to (VCC+ 0.3V)
DL to PGND................................................-0.3V to (VDD+ 0.3V)
CSN to AGND............................................................-2V to +30V
DH to LX.....................................................-0.3V to (BST + 0.3V)
LX to AGND...............................................................-2V to +30V
BST to LX..................................................................-0.3V to +6V
AGND to PGND (MAX1992 only)..........................-0.3V to +0.3V
REF Short Circuit to AGND.........................................Continuous
Continuous Power Dissipation (TA= +70°C)
24-Pin 4mm x 4mm Thin QFN
(derated 20.8mW/°C above +70°C)...........................1667mW
Operating Temperature Range
MAX199_ETG..................................................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
Note 1:For the MAX1993, AGND and PGND refer to a single pin designated GND.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
PWM CONTROLLERVINBattery voltage, V+228Input Voltage RangeVBIASVCC, VDD4.55.5V
FB = GND2.4752.52.525
Output Voltage Accuracy
(MAX1992 Fixed)VOUT
MAX1992
V+ = 4.5V to 28V,
SKIP = VCC
(Note 2)FB = VCC1.7821.81.818
Feedback Voltage Accuracy
(MAX1992 Adjustable)VFBMAX1992 V+ = 4.5V to 28V, SKIP = VCC
(Note 2)0.6930.70.707V
REFIN = 0.35 × REF0.6930.70.707
Feedback Voltage Accuracy
(MAX1993)VFB
MAX1993
V+ = 4.5V to 28V,
SKIP = VCC
(Note 2)REFIN = REF1.98022.020
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
FB = GND90190350MAX1992FB = VCC or adjustable70145270OUT Input ResistanceROUT
MAX19934008001400
OUT Discharge Mode
On-ResistanceRDISCHARGE1025Ω
OUT Synchronous Rectifier
Discharge Mode Turn-On Level0.20.30.4V
Soft-Start Ramp TimetSSRising edge on SHDN to full current limit1.7ms
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC = VDD = SHDN= 5V, SKIP= GND, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSTON = GND (600kHz)170194219
TON = REF (450kHz)213243273
TON = open (300kHz)316352389On-TimetON
V+ = 15V,
VOUT = 1.5V
(Note 3)
TON = VCC (200kHz)461516571
Minimum Off-TimetOFF(MIN)(Note 3)400500ns
FB forced above the regulation point,
LSAT = GND0.550.85
Quiescent Supply Current (VCC)ICC
FB forced above the regulation point,
VLSAT > 0.5V1
Quiescent Supply Current (VDD)IDDFB forced above the regulation point<15µA
Quiescent Supply Current (V+)IV+2540µA
Shutdown Supply Current (VCC)SHDN = GND<17µA
Shutdown Supply Current (VDD)SHDN = GND<15µA
Shutdown Supply Current (V+)SHDN = GND, V+ = 28V,
VCC = VDD = 0 or 5V<15µA
REFERENCETA = +25°C to +85°C1.98622.014Reference VoltageVREFVCC = 4.5V to 5.5V,
IREF = 0TA = 0°C to +85°C1.98322.017V
Reference Load RegulationΔVREFIREF = -10µA to 50µA-0.01+0.01V
REF Lockout VoltageVREF(UVLO)Rising edge, hysteresis = 350mV1.95V
REFIN Voltage Range0.7VREFV
REFIN Input Bias CurrentIREFIN0.010.05µA
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 SHDN1035ms
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 DelaytPGOODFB forced 2% beyond PGOOD trip
threshold10µs
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC = VDD = SHDN= 5V, SKIP= GND, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSPGOOD Output Low VoltageISINK = 4mA0.3V
PGOOD Leakage CurrentIPGOODFB = REF (PGOOD high impedance),
PGOOD forced to 5.5V1µA
FBLANK = VCC120218320
FBLANK = open80140205Fault Blanking TimetFBLANK
FBLANK = REF356395
Thermal Shutdown ThresholdTSHDNHysteresis = 15°C160°C
VCC Undervoltage Lockout
ThresholdVUVLO(VCC)Rising edge, PWM disabled below this level
hysteresis = 20mV4.14.254.4V
CURRENT LIMITILIM Adjustment Range0.252.00V
CSP02.7Current-Limit Input RangeCSN-0.3+28.0V
CSP/CSN Input Current-0.5+0.5µA
Valley Current-Limit Threshold
(Fixed)VLIM(VAL)VCSP - VCSN, ILIM = VCC455055mV
VILIM = 250mV152535Valley Current-Limit Threshold
(Adjustable)VLIM(VAL)VCSP - VCSNVILIM = 2.00V170200230mV
Current-Limit Threshold
(Negative)VNEGVCSP - VCSN, SKIP = ILIM = VCC,
TA = +25°C-75-60-45mV
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
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC = VDD = SHDN= 5V, SKIP= GND, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSDL 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 ThresholdSHDN, SKIP, GATE
rising edge, hysteresis = 225mV1.201.72.20V
Logic Input CurrentSHDN, SKIP, GATE-1+1µA
High1.92.02.1Dual Mode™ Threshold VoltageMAX1992 FBLow0.050.10.15V
HighVCC -
0.4V
Open3.153.85
REF1.652.35
Four-Level Input Logic LevelsTON, OVP/UVP,
LSAT, FBLANK
Low0.5
Four-Level Logic Input CurrentTON, OVP/UVP, LSAT,
FBLANK forced to GND or VCC-3+3µA
ELECTRICAL CHARACTERISTICS(V+ = 15V, VCC = VDD = SHDN= 5V, SKIP= GND, TA
= -40°C to +85°C, unless otherwise noted.) (Note 4)
PARAMETERSYMBOLCONDITIONSMINMAXUNITS
PWM CONTROLLERVINBattery voltage, V+228Input Voltage RangeVBIASVCC, VDD4.55.5V
FB = GND2.4622.538
Output Voltage Accuracy
(MAX1992 Fixed)VOUT
MAX1992,
V+ = 4.5V to 28V,
SKIP = VCC
(Note 2)FB = VCC1.7731.827
Feedback Voltage Accuracy
(MAX1992 Adjustable)VFBMAX1992, V+ = 4.5V to 28V, SKIP = VCC
(Note 2)0.6890.711V
REFIN = 0.35 × REF0.6890.711
Feedback Voltage Accuracy
(MAX1993)VFB
MAX1993,
V+ = 4.5V to 28V,
SKIP = VCC
(Note 2)REFIN = REF1.9702.030
TON = GND (600kHz)170219
TON = REF (450kHz)213273
TON = open (300kHz)316389On-TimetON
V+ = 15V,
VOUT = 1.5V
(Note 3)
TON = VCC (200kHz)461571
Dual Mode is a trademark of Maxim Integrated Products, Inc.
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC = VDD = SHDN= 5V, SKIP= GND, TA
= -40°C to +85°C, unless otherwise noted.) (Note 4)
PARAMETERSYMBOLCONDITIONSMINMAXUNITSMinimum Off-TimetOFF(MIN)(Note 3)500ns
FB forced above the regulation point,
LSAT = GND0.85
Quiescent Supply Current (VCC)ICC
FB forced above the regulation point,
VLSAT > 0.5V1.0
Quiescent Supply Current (VDD)IDDFB forced above the regulation point5µA
Quiescent Supply Current (V+)IV+40µA
Shutdown Supply Current (VCC)SHDN = GND7µA
Shutdown Supply Current (VDD)SHDN = GND5µA
Shutdown Supply Current (V+)SHDN = GND, V+ = 28V,
VCC = VDD = 0 or 5V5µA
REFERENCEReference VoltageVREFVCC = 4.5V to 5.5V, IREF = 01.9802.020V
REFIN Voltage Range0.7VREFV
FAULT DETECTIONOvervoltage Trip ThresholdWith respect to error comparator threshold,
OVP/UVP = VCC1020%
Output Undervoltage Protection
Trip Threshold
With respect to error comparator threshold,
OVP/UVP = VCC6575%
PGOOD Lower Trip ThresholdWith respect to error comparator threshold,
hysteresis = 1%-14-6%
PGOOD Upper Trip ThresholdWith respect to error comparator threshold,
hysteresis = 1%+6+14%
VCC Undervoltage Lockout
ThresholdVUVLO(VCC)Rising edge, PWM disabled below this level
hysteresis = 20mV4.14.4V
CURRENT LIMITCSP02.7Current-Limit Input RangeCSN-0.3+28.0V
Valley Current-Limit Threshold
(Fixed)VLIM(VAL)VCSP - VCSN, ILIM = VCC3565mV
Valley Current-Limit Threshold
(Adjustable)VLIM(VAL)VCSP - VCSN, VILIM = 2.00V160240mV
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
ELECTRICAL CHARACTERISTICS (continued)(V+ = 15V, VCC = VDD = SHDN= 5V, SKIP= GND, TA
= -40°C to +85°C, unless otherwise noted.) (Note 4)
PARAMETERSYMBOLCONDITIONSMINMAXUNITS
INPUTS AND OUTPUTSLogic Input ThresholdSHDN, SKIP, GATE
rising edge, hysteresis = 225mV1.202.20V
High1.92.1Dual Mode Threshold VoltageMAX1992 FBLow0.050.15V
HighVCC -
0.4V
Open3.153.85
REF1.652.35
Four-Level Input Logic LevelsTON, OVP/UVP,
LSAT, FBLANK
Low0.5
Note 2:When the inductor is in continuous conduction, the output voltage has a DC regulation level higher than the error compara-
tor threshold by 50% of the output 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 can differ due to MOSFET switching speeds.
Note 4:Specifications to -40°C are guaranteed by design, not production tested.
Typical Operating Characteristics(MAX1992 Circuit of Figure1, MAX1993 Circuit of Figure9, VIN = 12V, VDD= VCC= 5V, SKIP= VCC, TON = open, TA = +25°C,
unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(VOUT = 2.5V)MAX1992 toc01
LOAD CURRENT (A)
EFFICIENCY (%)0.1
VIN = 7V
VIN = 12V
VIN = 20V
SKIP = GND
SKIP = VCC
2.5V OUTPUT VOLTAGE
vs. LOAD CURRENTMAX1992 toc02
LOAD CURRENT (A)
OUTPUT VOLTAGE (V)312
SKIP = GND
SKIP = VCC
VIN = 7V
VIN = 20V
EFFICIENCY vs. LOAD CURRENT
(VOUT = 1.8V)MAX1992 toc03
LOAD CURRENT (A)
EFFICIENCY (%)0.1
VIN = 7V
VIN = 12V
VIN = 20V
SKIP = GND
SKIP = VCC
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
Typical Operating Characteristics (continued)(MAX1992 Circuit of Figure 1, MAX1993 Circuit of Figure 9, VIN = 12V, VDD= VCC= 5V, SKIP= VCC, TON = open, TA = +25°C,
unless otherwise noted.)
1.8V OUTPUT VOLTAGE
vs. LOAD CURRENTMAX1992 toc04
LOAD CURRENT (A)
OUTPUT VOLTAGE (V)321
SKIP = GND
SKIP = VCC
VIN = 7V
VIN = 20V
SWITCHING FREQUENCY
vs. LOAD CURRENTMAX1992 toc05
LOAD CURRENT (A)
SWITCHING FREQUENCY (kHz)312
SKIP = GND
SKIP = VCC
SWITCHING FREQUENCY
vs. INPUT VOLTAGEMAX1992 toc06
INPUT VOLTAGE (V)
SWITCHING FREQUENCY (kHz)20161284
NO LOAD
4A LOAD
SWITCHING FREQUENCY
vs. TEMPERATUREMAX1992 toc07
TEMPERATURE (°C)
SWITCHING FREQUENCY (kHz)3510-15
4A LOAD
NO LOAD
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGEMAX1992 toc08
INPUT VOLTAGE (V)
MAXIMUM I
OUT
(A)20161284
MAXIMUM OUTPUT CURRENT
vs. TEMPERATURE
MAX1992 toc09
TEMPERATURE (°C)
MAXIMUM I
OUT
(A)35-1510
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
(FORCED-PWM MODE)
MAX1992 toc10
INPUT VOLTAGE (V)
SUPPLY CURRENT (mA)20121684
IBIAS
IIN
SKIP = VCC
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
(SKIP MODE)MAX1992 toc11
INPUT VOLTAGE (V)
SUPPLY CURRENT (mA)20161284
IIN
IBIAS
SKIP = AGND
REFERENCE LOAD REGULATIONMAX1992 toc12
IREF (μA)
REFERENCE VOLTAGE (V)6040200
-20100
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
ILIM SATURATION FAULT CURRENT
vs. ILIM VOLTAGEMAX1992 toc13
VILIM (V)
ILIM(LSAT)
STARTUP WAVEFORMS
(HEAVY LOAD)
MAX1992 toc14
400μs/div
A. SHDN = 0 TO 5V; 5V/div
B. INDUCTOR CURRENT: 2A/div
C. OUTPUT VOLTAGE (VOUT): 2V/div
D. PGOOD: 5V/div, 0.7Ω LOAD
STARTUP WAVEFORMS
(LIGHT LOAD)MAX1992 toc15
200μs/div
A. SHDN = 0 TO 5V; 5V/div
B. INDUCTOR CURRENT: 2A/div
C. OUTPUT VOLTAGE (VOUT): 2V/div
D. PGOOD: 5V/div, 100Ω LOAD
SHUTDOWN WAVEFORMS
(DISCHARGE MODE DISABLED)MAX1992 toc16
20ms/div
A. SHDN = 5V TO 0; 5V/div
B. INDUCTOR CURRENT: 2A/div
C. DL: 5V/div
D. OUTPUT VOLTAGE (VOUT): 2V/div
E. PGOOD: 5V/div, 100Ω LOAD, OVP/UVP = OPEN OR G
SHUTDOWN WAVEFORMS
(DISCHARGE MODE ENABLED)MAX1992 toc17
1.0ms/div
A. SHDN = 5V TO 0; 5V/div
B. INDUCTOR CURRENT: 2A/div
C. DL: 5V/div
D. OUTPUT VOLTAGE (VOUT): 2V/div
E. PGOOD: 5V/div, 100Ω LOAD, OVP/UVP = VCC OR REF
2.5V
LOAD TRANSIENT
(FORCED-PWM OPERATION)MAX1992 toc18
20μs/div
A. LOAD: IOUT = 0.2A TO 4A; 5A/div
B. 2.5V OUTPUT: 100mV/div
C. INDUCTOR CURRENT: 5A/div
D. LX: 10V/div, SKIP = VCC
2.5V
2.4V
2.6V
12V
Typical Operating Characteristics (continued)(MAX1992 Circuit of Figure 1, MAX1993 Circuit of Figure 9, VIN = 12V, VDD= VCC= 5V, SKIP= VCC, TON = open, TA = +25°C,
unless otherwise noted.)
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
Typical Operating Characteristics (continued)(MAX1992 Circuit of Figure 1, MAX1993 Circuit of Figure 9, VIN = 12V, VDD= VCC= 5V, SKIP= VCC, TON = open, TA = +25°C,
unless otherwise noted.)
LOAD TRANSIENT
(PULSE-SKIPPING OPERATION)MAX1992 toc19
20μs/div
A. LOAD: IOUT = 0.2A TO 4A; 5A/div
B. 2.5V OUTPUT: 100mV/div
C. INDUCTOR CURRENT: 5A/div
D. LX: 10V/div, SKIP = GND
2.5V
2.4V
2.6V
12V
OUTPUT OVERLOAD WAVEFORMS
(UVP DISABLED)MAX1992 toc20
40μs/div
A. LOAD CURRENT (0 TO 250mΩ): 10A/div
B. 2.5V OUTPUT: 2V/div
C. INDUCTOR CURRENT: 5A/div
D. PGOOD: 5V/div, OVP/UVP = OPEN OR GND
2.5V
10A
OUTPUT OVERLOAD WAVEFORMS
(UVP ENABLED)MAX1992 toc21
20μs/div
A. LOAD CURRENT (0 TO 250mΩ): 10A/div
B. 2.5V OUTPUT: 2V/div
C. DL: 5V/div
D. INDUCTOR CURRENT: 5A/div
E. PGOOD: 5V/div, OVP/UVP = VCC OR REF
2.5V
10A
INDUCTOR SATURATION PROTECTION
(LSAT DISABLED)MAX1992 toc22
20μs/div
A. LOAD CURRENT: IOUT = 0 TO 5A; 5A/div
B. 2.5V OUTPUT: 200mV/div
C. VILIM: 100mV/div
D. INDUCTOR CURRENT: 5A/div;
LSAT = AGND; L = 3.3μH, 3.5A
2.5V
7.5A
0.67V
INDUCTOR SATURATION PROTECTION
(ΔVILIM = 200mV)MAX1992 toc23
20μs/div
A. LOAD CURRENT: IOUT = 0 TO 5A; 5A/div
B. 2.5V OUTPUT: 200mV/div
C. VILIM: 200mV/div
D. INDUCTOR CURRENT: 5A/div,
LSAT = REF; L = 3.3μH, 3.5A
2.5V
7.5A
0.67V
0.47V
INDUCTOR SATURATION PROTECTION
(ΔVILIM = 400mV)MAX1992 toc24
20μs/div
A. LOAD CURRENT: IOUT = 0 TO 5A; 5A/div
B. 2.5V OUTPUT: 1V/div
C. PGOOD: 5V/div
D. VILIM: 400mV/div
E. INDUCTOR CURRENT: 5A/div,
LSAT = REF; L = 3.3μH, 3.5A
2.5V
7.5A0.67V
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
MAX1993 DYNAMIC OUTPUT VOLTAGE
TRANSITION (CREFIN = 1nF)MAX1992 toc25
100μs/div
1.5V
1.5V
2.5A
-2.5A
1.0V
A. VGATE = 0 TO 5V; 5V/div
B. OUTPUT = 1.5V TO 1.0V; 0.5V/div
C. VREFIN: 0.5V/div
D. PGOOD: 5V/div
E. INDUCTOR CURRENT: 2.5A/div
100mA LOAD, SKIP = GND, CIRCUIT OF FIGURE 9
MAX1993 DYNAMIC OUTPUT VOLTAGE
TRANSITION (CREFIN = 100pF)MAX1992 toc26
40μs/div
1.5V
1.5V
-5A
1.0V
A. VGATE = 0 TO 5V; 5V/div
B. OUTPUT = 1.5V TO 1.0V; 0.5V/div
C. VREFIN: 0.5V/div
D. PGOOD: 5V/div
E. INDUCTOR CURRENT: 2.5A/div
100mA LOAD, SKIP = GND, CIRCUIT OF FIGURE 9
Typical Operating Characteristics (continued)(MAX1992 Circuit of Figure 1, MAX1993 Circuit of Figure 9, VIN = 12V, VDD= VCC= 5V, SKIP= VCC, TON = open, TA = +25°C,
unless otherwise noted.)
Pin Description
PIN
MAX1992MAX1993NAMEFUNCTIONTON
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 section). Connect to
analog ground (AGND or GND), REF, VCC, or leave TON unconnected to select the
following nominal switching frequencies:
VCC = 200kHz
Open = 300kHz
REF = 450kHz
AGND = 600kHz
2, 7, 8—N.C.No Connection. Not internally connected.2FBLANK
Fault Blanking Control Input. This four-level logic input enables or disables fault
blanking, and sets the minimum forced-PWM operation time (tFBLANK). When fault
blanking is enabled, PGOOD, OVP protection, and UVP protection are blanked for the
selected time period after a transition is detected on GATE. Additionally, the controller
enters forced-PWM mode for the duration of tFBLANK anytime GATE changes states.
Connect FBLANK as follows:
VCC = 140µs (min) tFBLANK, fault blanking enabled
Open = 90µs (min) tFBLANK, fault blanking enabled
REF = 40µs (min) tFBLANK, fault blanking enabled
AGND = 90µs (min) tFBLANK, fault blanking disabled
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
Pin Description (continued)
PIN
MAX1992MAX1993NAMEFUNCTION3LSAT
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 × ILIM(VAL)
Open = 1.75 × ILIM(VAL)
REF = 1.5 × ILIM(VAL)
AGND = disable LSAT protection
See the Inductor Saturation Limit and Setting the Current Limit sections.4PGOOD
Open-Drain Power-Good Output. PGOOD 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, PGOOD becomes high
impedance if the output is in regulation. For the MAX1993, PGOOD is
blanked—forced high-impedance state—when FBLANK is enabled and the controller
detects a transition on GATE.5ILIM
Valley Current-Limit Threshold Adjustment. The valley current-limit threshold defaults
to 50mV if ILIM is tied to VCC. In adjustable mode, the valley current-limit threshold
across CSP and CSN is precisely 1/10th the voltage seen at ILIM 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, ILIM sinks 6µA. See the Current-Limit Protection (ILIM) section.6REF
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 MAX1992/MAX1993 is shut down.7REFINExternal Reference Input. REFIN sets the feedback regulation voltage (VFB = VREFIN)
of the MAX1993.8ODOpen-Drain Output. Controlled by GATE.FB
Feedback Input.
MAX1992: Connect to VCC for a +1.8V fixed output or to AGND for a +2.5V fixed
output. For an adjustable output (0.7V to 5.5V), connect FB to a resistive divider from
the output voltage. The FB regulation level is +0.7V.
MAX1993: The FB regulation level is set by the voltage at REFIN.10OUT
Output Voltage Sense. Connect directly to the positive terminal of the output
capacitors as shown in the standard application circuits (Figures 1 and 9). OUT
senses the output voltage to determine the on-time for the high-side switching
MOSFET. For the MAX1992, OUT also serves as the feedback input when using the
preset internal output voltages as shown in Figure 7. When discharge mode is
enabled by OVP/UVP, the output capacitor is discharged through an internal 10Ω
resistor connected between OUT and ground.11CSP
Positive Current-Sense Input. Connect to the positive terminal of the current-sense
element. Figure 10 and Table 7 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 ILIM.
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
Pin Description (continued)
PIN
MAX1992MAX1993NAMEFUNCTION12CSN
Negative Current-Sense Input. Connect to the negative terminal of the current-sense
element. Figure 10 and Table 7 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 ILIM.13SKIP
Pulse-Skipping Control Input. Connect SKIP to VCC for low-noise, forced-PWM mode
or connect SKIP to analog ground (AGND or GND) to enable pulse-skipping
operation.14V+
Battery Voltage-Sense Connection. The controller only 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.15DHHigh-Side Gate-Driver Output. DH swings from LX to BST.16LXInductor Connection. Connect LX to the switched side of the inductor. LX serves as
the lower supply rail for the DH high-side gate driver.17BST
Boost Flying Capacitor Connection. Connect to an external capacitor and diode as
shown in Figure 6. An optional resistor in series with BST allows the DH pullup current
to be adjusted.18DLLow-Side Gate-Driver Output. DL swings from PGND to VDD (MAX1992) or GND to
VDD (MAX1993).19VDDSupply Voltage Input for the DL Gate Driver. Connect to the system supply voltage
(+4.5V to +5.5V). Bypass VDD to PGND with a 1µF or greater ceramic capacitor.—PGNDPower Ground. Ground connection for the DL low-side gate driver.20GNDAnalog and Power Ground. AGND and PGND connect together internally. Connect
backside pad to GND.—AGNDAnalog Ground. Connect backside pad to AGND.21GATE
Buffered N-Channel MOSFET Gate Input. A logic low on GATE turns off the internal
MOSFET so OD appears as a high impedance. A logic high on GATE turns on the
internal MOSFET, pulling OD to ground.22VCC
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.
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
Pin Description (continued)
PIN
MAX1992MAX1993NAMEFUNCTION23SHDN
Shutdown Control Input. Connect to VCC for normal operation. Connect to analog
ground to put the controller into its 1µA shutdown state. When discharge mode is
enabled by OVP/UVP, the output is discharged through a 10Ω resistor between OUT
and ground, and DL is forced high after VOUT drops below 0.3V. When discharge
mode is disabled by OVP/UVP, OUT remains a high-impedance input and DL is
forced low, so LX also appears as a high-impedance input. A rising edge on SHDN
clears the fault-protection latch.24OVP/UVP
Overvoltage/Undervoltage Protection and Discharge Mode Control Input. This four-
level logic input selects between various output fault-protection options (Table 6) 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 UVP 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
AGND = disable OVP and discharge mode, and UVP
See the Fault Protection and Shutdown and Output Discharge sections.
Table 1. Component Selection for Standard Applications
VOUT = 2.5V AT 5A
(FIGURE 1)VOUT = 1.8V AT 5AVOUT = 1.0V / 1.5V AT 4A
(FIGURE 9)COMPONENTVIN = 7V to 24V,
TON = OPEN (300kHz)
VIN = 7V to 24V,
TON = OPEN (300kHz)
VIN = 4.5V to 5.5V,
TON = GND (600kHz)
MAX1992FB = AGNDFB = VCCNot recommended
MAX1993Adjustable FB,
REFIN = REF
FB = OUT,
VREFIN = 1.8V
FB = OUT,
VREFIN = 1.0V / 1.5V
CIN, input capacitor10µF, 25V
Taiyo Yuden TMK432BJ106KM
10µF, 25V
Taiyo Yuden TMK432BJ106KM
100µF, 10V
Sanyo POSCAP 10TPA100M
COUT, output capacitor220µF, 4V, 15mΩ
Sanyo POSCAP 4TPE220MF
220µF, 4V, 15mΩ
Sanyo POSCAP 4TPE220MF
220µF, 6V, 12mΩ
Sanyo POSCAP 6TPD220M
NH high-side MOSFETFairchild Semiconductor
1/2 FDS6982A
Fairchild Semiconductor
1/2 FDS6982A
Fairchild Semiconductor
1/2 FDS6982S
NL low-side MOSFETFairchild Semiconductor
1/2 FDS6982A
Fairchild Semiconductor
1/2 FDS6982A
Fairchild Semiconductor
1/2 FDS6982S
DL Schottky rectifier
(optional)
Nihon EP10QS03L
1A, 30V, 0.45Vf
Nihon EP10QS03L
1A, 30V, 0.45Vf
Nihon EP10QS03L
1A, 30V, 0.45Vf
L1 inductor4.3µH
Sumida CDEP105(L)
3.2µH
Sumida CDEP105(L)
1.4µH
Sumida CDEP105(L)
RSENSE
15mΩ ±1% 0.5W resistor
IRC LR2010-01-R015F or
Dale WSL-2010-R015F
15mΩ ±1% 0.5W resistor
IRC LR2010-01-R015F or
Dale WSL-2010-R015F
15mΩ ±1% 0.5W resistor
IRC LR2010-01-R015F or
Dale WSL-2010-R015F
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
Table 2. Component Suppliers
SUPPLIERPHONEWEBSITECentral Semiconductor631-435-1110 (USA)www.centralsemi.com
Coilcraft800-322-2645 (USA)www.coilcraft.com
Coiltronics561-752-5000 (USA)www.coiltronics.com
Fairchild Semiconductor888-522-5372 (USA)www.fairchildsemi.com
International Rectifier310-322-3331 (USA)www.irf.com
Kemet408-986-0424 (USA)www.kemet.com
Panasonic714-373-7366 (USA)www.panasonic.com
Sanyo65-231-3226 (Singapore)
408-749-9714 (USA)www.secc.co.jp
Siliconix (Vishay)203-268-6261 (USA)www.vishay.com
Sumida408-982-9660 (USA)www.sumida.com
Taiyo Yuden03-3667-3408 (Japan)
408-573-4150 (USA)www.t-yuden.com
TDK847-803-6100 (USA)
81-3-5201-7241 (Japan)www.component.tdk.com
TOKO858-675-8013 (USA)www.tokoam.com
MAX1992
POWER GOOD
ON OFF
FLOAT
(300kHz)
1μF
1μF
OUTPUT (VOUT)
2.5V
COUT
220μF
INPUT (VIN)*
7V TO 20V
+5V BIAS
SUPPLY
DBST
CMPSH-3
CBST
0.1μF
4.3μH
RSENSE
15mΩ
CIN
10μF
VCCVDD
SHDN
PGOOD
LSAT
SKIP
REF
ILIM
ANALOG GROUND
*LOWER INPUT VOLTAGES REQUIRE
ADDITIONAL INPUT CAPACITANCE.
SEE TABLE 1 FOR COMPONENT SPECIFICATIONS.BOLD LINES INDICATE HIGH CURRENT TRACES.
OVP/UVP
OUT
CSN
CSP
PGND
BST
20Ω
TONLX
AGND
100kΩ
CREF
0.22μF
CILIM
470pF
100kΩ
49.9kΩ
POWER GROUND
Figure 1. MAX1992 Standard Application Circuit
MAX1992/MAX1993
Detailed DescriptionThe MAX1992/MAX1993 buck controllers are ideal for
low-voltage power supplies for notebook computers.
Maxim’s proprietary Quick-PWM pulse-width modulator
in the MAX1992/MAX1993 is designed for handling fast
load steps while maintaining a relatively constant oper-
ating frequency and inductor operating point over a
wide range of input voltages. The Quick-PWM architec-
ture circumvents the poor load-transient timing prob-
lems of fixed-frequency current-mode PWMs while
avoiding the problems caused by widely varying
switching frequencies in conventional constant-on-time
and constant-off-time PWM schemes.
See Table 1 for component selections and Table 2 for a
list of component suppliers.
+5V Bias Supply (VCCand VDD)The MAX1992/MAX1993 require an external 5V bias
supply in addition to the battery. Typically, this 5V bias
supply is the notebook’s 95%-efficient 5V system sup-
ply. Keeping the bias supply external to the IC improves
efficiency and eliminates the cost associated with the 5V
linear regulator that would otherwise be needed to sup-
ply the PWM circuit and gate drivers. If stand-alone
capability is needed, the 5V supply can be generated
with an external linear regulator such as the MAX1615.
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))
= 2mA to 20mA (typ)
where ICCis 550µA (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 is powered
up prior to the battery supply, the enable signal (SHDN
going from low to high) must be delayed until the bat-
tery 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 (Figure2). 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 control algorithm is
simple: the high-side switch on-time is determined sole-
ly by a one-shot whose pulse width is inversely propor-
tional to input voltage and directly proportional to
output voltage. Another one-shot sets a minimum off-
time (400ns typ). The on-time one-shot is triggered if
the error comparator is low, the low-side switch current
is below the valley current-limit threshold, and the mini-
mum 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 battery and output voltage. The high-side
switch on-time is inversely proportional to the battery
voltage as measured by the V+ input and is proportional
to the output voltage:
On-time = K (VOUT+ 0.075V) / VIN
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
Table 3. Approximate K-Factor Errors
TON SETTING
(kHz)
TYPICAL
K-FACTOR (µs)
K-FACTOR
ERROR (%)
MINIMUM VIN
AT VOUT = 2.5V
(h = 1.5) (V)
TYPICAL
APPLICATIONCOMMENTS(TON = VCC)5.0±103.144-cell Li+ notebookUse for absolute best efficiency
(TON = open)3.3±103.474-cell Li+ notebookConsidered mainstream by
current standards
(TON = REF)2.2±12.54.133-cell Li+ notebook
Useful in 3-cell systems for
lighter loads than the CPU core
or where size is key
(TON = GND)1.7±12.55.61+5V input
Good operating point for
compound buck designs or
desktop circuits
MAX1992/MAX1993
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output VoltagesMAX1992
MAX1993
MAX1993
ONLY
OUT
ILIM
OVP/UVP
SKIP
CSPZERO CROSSING
CSN
*OD
PGOOD
*GATE
*FBLANK
BLANK
1-SHOT
tOFF(MIN)
TRIGQ
BST
ON-TIME
COMPUTE
TON
TRIG
1-SHOT
ERROR
AMP
ENABLE
OVP
ENABLE
UVP
1.14 x
INTREF
0.7 x
INTREF
0.9 x
INTREF
1.1 x
INTREF
tON
QUAD
LEVEL
DECODE
FBLANK
DECODE
AND TIMER
FAULT
LATCH
BLANK
20ms
TIMER
PORQ
LSAT
PGND
VDD
CSP
CSN
0.5V
QUAD
LEVEL
DECODE
SATURATION
LIMIT
CSP
ILIM
*REFIN
13R
0.7V
OUT
SHDN
REF
VCC
AGND
VCC - 1.0V
CSNCURRENT
LIMIT
INTREF
2.0V
REF
MAX1992
FB DECODE
(FIGURE 7)
*MAX1993 ONLY. IN THE MAX1993, AGND AND PGND
ARE INTERNALLY CONNECTED AND CALLED GND.
DISCHARGE
LOGIC
MAX1992 vs. MAX1993
INTERNAL OPTION
Figure 2. MAX1992/MAX1993 Functional Diagram
MAX1992/MAX1993where K (switching period) is set by the TON pin-strap
connection (Table3), and 0.075V is an approximation to
accommodate the expected drop across the low-side
MOSFET switch. This algorithm results in a nearly con-
stant switching frequency despite the lack of a fixed-fre-
quency 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; 2) the inductor ripple-current operating
point remains relatively constant, resulting in easy design
methodology and predictable output voltage ripple.
The on-time one-shot has good accuracy at the operat-
ing points specified in the Electrical Characteristics
(approximately ±12.5% at 600kHz and 450kHz and
±10% at 200kHz and 300kHz). On-times at operating
points far removed from the conditions specified in the
Electrical Characteristicscan vary over a wider range.
For example, the 600kHz setting typically runs approxi-
mately 10% slower with inputs much greater than 5V
due to the very short on-times required.
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,
output capacitor ESR, and PC board copper losses in the
output and ground—tend to raise the switching frequency
as the load increases. The dead-time effect increases the
effective on-time, reducing the switching frequency as
one or both dead times are added 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 DH-rising dead time.
For loads above the critical conduction point, where the
dead-time effect is no longer a factor, the actual switch-
ing 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-
ing the high-side switch, inductor, and PC board resis-
tances; and tONis the on-time calculated by the
MAX1992/MAX1993.
Automatic Pulse-Skipping Mode
(SKIP= GND)In skip mode (SKIP= GND), an inherent automatic
switchover to PFM takes place at light loads (Figure3).
This switchover is affected by a comparator that trun-
cates the low-side switch on-time at the inductor cur-
rent’s zero crossing. The zero-crossing comparator
differentially senses the inductor current across the cur-
rent-sense resistor (CSP to CSN). Once VCSP- VCSN
drops below 5% of the current-limit threshold (2.5mV
for the default 50mV current-limit threshold), the com-
parator forces DL low (Figure2). This mechanism caus-
es the threshold between pulse-skipping PFM and
nonskipping PWM operation to coincide with the
boundary between continuous 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
one-half the peak-to-peak ripple current, which is a
function of the inductor value (Figure3). This threshold
is relatively constant, with only a minor dependence on
battery voltage:
where K is the on-time scale factor (Table3). For exam-
ple, in the standard application circuit (K = 3.3µs, VOUT=
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 can 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).33325076...VsA×⎜⎞⎟−⎛⎜⎞⎟=μVKLOADSKIPOUTINOUT≈⎛⎜⎞⎟⎛⎜⎟VVVSWOUTDROPINDROP+()
Quick-PWM Step-Down Controllers with Inductor
Saturation Protection and Dynamic Output Voltages
