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MAX8743EEI+-MAX8743EEI+T-MAX8743ETX+
Dual, High-Efficiency, Step-Down Controller with High Impedance in Shutdown
General DescriptionThe MAX8743 is a dual pulse-width modulation (PWM)
controller configured for step-down (buck) topologies
that provides the high efficiency, excellent transient
response, and high DC output accuracy necessary for
stepping down high-voltage batteries to generate low-
voltage chipset and RAM power supplies in notebook
computers. The CS_ inputs can be used with low-side
sense resistors to provide accurate current limits or can
be connected to LX_, using low-side MOSFETs as cur-
rent-sense elements. High output impedance in shut-
down eliminates negative output voltages, saving the
cost of a Schottky diode at the output.
The on-demand PWM controllers are free running, con-
stant on-time with input feed-forward. This configuration
provides ultra-fast transient response, wide input-output
differential range, low supply current, and tight load-reg-
ulation characteristics. The MAX8743 is simple and easy
to compensate.
Single-stage buck conversion allows the MAX8743 to
directly step down high-voltage batteries for the highest
possible efficiency. Alternatively, two-stage conversion
(stepping down the 5V system supply instead of the bat-
tery at a higher switching frequency) allows the minimum
possible physical size.
The MAX8743 is intended for generating chipset, DRAM,
CPU I/O, or other low-voltage supplies down to 1V. The
MAX8743 is available in 28-pin QSOP and 36-pin thin
QFN packages.
ApplicationsNotebook Computers
CPU Core Supplies
Chipset/RAM Supplies as Low as 1V
1.8V and 2.5V I/O Supplies
FeaturesUltra-High EfficiencyAccurate Current-Limit OptionQuick-PWM™with 100ns Load-Step Response1% VOUTAccuracy over Line and LoadHigh Output Impedance in ShutdownDual Mode™Fixed 1.8V/1.5V/Adj or 2.5V/Adj OutputsAdjustable 1V to 5.5V Output Range2V to 28V Battery Input Range200kHz/300kHz/420kHz/540kHz Nominal Switching
FrequencyAdjustable Overvoltage Protection1.7ms Digital Soft-StartDrives Large Synchronous-Rectifier FETsPower-Good Window Comparator2V ±1% Reference Output
MAX8743
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown19-3318; Rev 1; 8/05
Pin Configurations appear at end of data sheet.Quick-PWM and Dual Mode are trademarks of Maxim Integrated
Products, Inc.
VCC
OUTPUT1
1.8V
BATTERY
4.5V TO 28V
ILIM1
ON2
DL1
TON
OUT1
LX1
DH1
FB1
GND
VDD
BST1
ILIM2
ON1
REF
DL2
CS2
OUT2
LX2
DH2
FB2
BST2
SKIP
5V INPUT
PGOOD
OUTPUT2
2.5V
MAX8743EEI
UVP
OVP
CS1
Minimal Operating Circuit
Ordering Information
PARTTEMP RANGEPIN-PACKAGEMAX8743EEI-40°C to +85°C28 QSOP
MAX8743EEI+-40°C to +85°C28 QSOP
+Denotes lead-free package.
Ordering Information continued at end of data sheet.
MAX8743
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
ABSOLUTE MAXIMUM RATINGS (Note 1)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..............................................................-0.3 to +30V
VCCto AGND............................................................-0.3V to +6V
VDDto PGND............................................................-0.3V to +6V
AGND to PGND.....................................................-0.3V to +0.3V
PGOOD, OUT_ to AGND..........................................-0.3V to +6V
OVP, UVP, ILIM_, FB_, REF,
SKIP, TON, ON_ to AGND......................-0.3V to (VCC+ 0.3V)
DL_ to PGND..............................................-0.3V to (VDD+ 0.3V)
BST_ to AGND........................................................-0.3V to +36V
CS_ to AGND.............................................................-6V to +30V
DH1 to LX1..............................................-0.3V to (VBST1 + 0.3V)
LX_ to BST_..............................................................-6V to +0.3V
DH2 to LX2..............................................-0.3V to (VBST2 + 0.3V)
REF Short Circuit to GND...........................................Continuous
Continuous Power Dissipation (TA= +70°C)
28-Pin QSOP (derate 10.8mW/°C above +70°C)........860mW
36-Pin 6mm ✕6mm Thin QFN
(derate 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(Circuit of Figure 1, VDD= VCC = 5V, SKIP= AGND, V+ = 15V, TA
= 0°C to +85°C, typical values are at +25°C, unless otherwisenoted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
PWM CONTROLLERSBattery voltage, V+228Input Voltage RangeVCC/VDDVCC, VDD4.55.5V
FB1 to AGND1.7821.81.818
FB1 to VCC1.4851.51.515
V+ = 2V to 28V, ILOAD
= 0 to 8A, SKIP = VCC,
+25°C to +85°CFB1 to OUT10.9911.01
FB1 to AGND1.7731.81.827
FB1 to VCC1.4771.51.523
DC Output Voltage OUT1
(Note 2)VOUT1
V+ = 2V to 28V, ILOAD
= 0 to 8A, SKIP = VCC,
0°C to +85°CFB1 to OUT10.98511.015
FB2 to AGND2.4752.52.525V+ = 4.5V to 28V,
ILOAD = 0 to 4A,
SKIP = VCC,
+25°C to +85°CFB2 to OUT20.9911.01
FB2 to AGND2.4632.52.537
DC Output Voltage OUT2
(Note 2)VOUT2V+ = 4.5V to 28V,
ILOAD = 0 to 4A,
SKIP = VCC,
0°C to +85°CFB2 to OUT20.98511.015
Output Voltage Adjust RangeOUT1, OUT215.5V
Dual-Mode Threshold, LowOVP, FB_0.050.10.15V
OVP, ILIM_VCC -
VCC -
0.4Dual-Mode Threshold, High
FB11.92.02.1
ROUT1VOUT1 = 1.5V75OUT_ Input ResistanceROUT2VOUT2 = 2.5V100kΩ
FB_ Input-Bias CurrentIFB-0.1+0.1µA
Soft-Start Ramp TimeZero to full ILIM1700µs
Note 1:For the MAX8743EEI, AGND and PGND refer to a single pin designated GND.
MAX8743
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
ELECTRICAL CHARACTERISTICS (continued)(Circuit of Figure 1, VDD= VCC = 5V, SKIP= AGND, V+ = 15V, TA
= 0°C to +85°C, typical values are at +25°C, unless otherwisenoted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSTON = AGND120137153
TON = REF153174195
TON = float222247272On-Time, Side 1tON1
V+ = 24V,
VOUT1 = 2V
(Note 3)
TON = VCC316353390
TON = AGND160182204
TON = REF205234263
TON = float301336371On-Time, Side 2tON2
V+ = 24V,
VOUT2 = 2V
(Note 3)
TON = VCC432483534
TON = AGND125135145
TON = REF125135145
TON = float125135145On-Time Tracking
On-time 2 with
respect to on-
time 1
(Note 3)TON = VCC125135145
Minimum Off-TimetOFF(Note 3)400500ns
Quiescent Supply Current (VCC)ICCFB_ forced above the regulation point11001500µA
Quiescent Supply Current (VDD)IDDFB_ forced above the regulation point<15µA
Quiescent Supply Current (V+)I+Measured at V+2570µA
Shutdown Supply Current (VCC)ON1 = ON2 = AGND, OVP = VCC<15µA
Shutdown Supply Current (VDD)ON1 = ON2 = AGND<15µA
Shutdown Supply Current (V+)ON1 = ON2 = AGND, measured at V+,
VCC = AGND or 5V<15µA
Reference VoltageVREFVCC = 4.5V to 5.5V, no external REF load1.9822.02V
Reference Load RegulationIREF = 0 to 50µA0.01V
REF Sink CurrentREF in regulation10µA
REF Fault Lockout VoltageFalling edge, hysteresis = 40mV1.6V
Overvoltage Trip Threshold
(Fixed-Threshold Mode)
OVP = AGND, with respect to error-
comparator trip threshold112114117%
1V < VOVP < 1.8V, external feedback,
measured at FB_ with respect to VOVP-280+28mV
Overvoltage Comparator Offset
(Adjustable-Threshold Mode)1V < VOVP < 1.8V, internal feedback,
measured at OUT_ with respect to OUT_
regulation point
-3.50+3.5%
OVP Input Leakage Current1V < VOVP < 1.8V-100<1+100nA
Overvoltage Fault Propagation
DelayFB_ forced 2% above trip threshold1.5µs
Output Undervoltage ThresholdUVP = VCC, with respect to error-comparator
trip threshold657075%
Output Undervoltage Protection
Blanking TimeFrom ON_ signal going high1030ms
MAX8743
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
ELECTRICAL CHARACTERISTICS (continued)(Circuit of Figure 1, VDD= VCC = 5V, SKIP= AGND, V+ = 15V, TA
= 0°C to +85°C, typical values are at +25°C, unless otherwisenoted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSCurrent-Limit Threshold (Fixed)AGND - VCS_, ILIM_ = VCC405060mV
AGND - VCS_, ILIM_ = 0.5V405060Current-Limit Threshold
(Adjustable)AGND - VCS_, ILIM_ = 1V85100115mV
ILIM_ Adjustment RangeVILIM_0.32.5V
Negative Current-Limit Threshold
(Fixed)VCS_ - AGND, ILIM_ = VCC, TA = +25 oC-75-60-45mV
Thermal-Shutdown ThresholdHysteresis = 15oC+160oC
VCC Undervoltage-Lockout
Threshold
Rising edge, hysteresis = 20mV, PWMs
disabled below this level4.054.40V
MAX8743EEI1.55ΩDH Gate-Driver On-ResistanceBST - LX forced to 5V
(Note 4)MAX8743ETX1.56Ω
MAX8743EEI1.55ΩDL Gate-Driver On-ResistanceDL, high state
(Note 4)MAX8743ETX1.56Ω
MAX8743EEI0.51.7ΩDL Gate-Driver On-ResistanceDL, low state
(Note 4)MAX8743ETX0.52.7Ω
DH_ Gate-Driver Source/Sink
CurrentVDH_ = 2.5V, VBST_ = VLX_ = 5V1A
DL_ Gate-Driver Sink CurrentVDL_ = 2.5V3A
DL_ Gate-Driver Source CurrentVDL_ = 2.5V1A
ON_, SKIP2.4
Logic Input High VoltageVIHUVPVCC -
ON_, SKIP0.8Logic Input Low VoltageVILUVP0.05V
VCC levelVCC -
Float level3.153.85
REF level1.652.35
TON Input Logic Level
AGND level0.5
Logic Input CurrentTON (AGND or VCC)-3+3µA
Logic Input CurrentON_, SKIP, UVP-1+1µA
PGOOD Trip Threshold (Lower)With respect to error-comparator trip
threshold, falling edge-12.5-10-7.5%
PGOOD Trip Threshold (Upper)With respect to error-comparator trip
threshold, rising edge+7.5+10+12.5%
PGOOD Propagation DelayFalling edge, FB_ forced 2% below PGOOD
trip threshold1.5µs
PGOOD Output Low VoltageISINK = 1mA0.4V
PGOOD Leakage CurrentHigh state, forced to 5.5V1µA
MAX8743
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
ELECTRICAL CHARACTERISTICS(Circuit of Figure 1, VDD= VCC = 5V, SKIP= AGND, V+ = 15V, TA
= -40°C to +85°C, unless otherwise noted.) (Note 5)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
PWM CONTROLLERSBattery voltage, V+228Input Voltage RangeVCC/VDDVCC, VDD4.55.5V
FB1 to AGND1.7731.827
FB1 to VCC1.4771.523D C O utp ut V ol tag e, O U T1VOUT1
V+ = 2V to 28V, SKIP = VCC,
ILOAD = 0 to 8AN ote 2) FB1 to OUT10.9851.015
FB2 to AGND2.4632.537D C O utp ut V ol tag e, O U T2VOUT2V+ = 2V to 28V, SKIP = VCC,
ILOAD = 0 to 4A ( N ote 2) FB2 to OUT20.9851.015V
Output Voltage Adjust RangeOUT1, OUT21.05.5V
Dual-Mode Threshold, LowOVP, FB_0.050.15V
OVP, ILIM_VCC -
VCC -
0.4Dual-Mode Threshold, High
FB_1.92.1
ROUT1VOUT1 = 1.5V75OUT_ Input ResistanceROUT2VOUT2 = 2.5V100kΩ
FB_ Input Bias CurrentIFB-0.1+0.1µA
TON = AGND120153
TON = REF153195
TON = float217272On-Time, Side 1tON1V+ = 24V, VOUT1 = 2V
(Note 3)
TON = VCC308390
TON = AGND160204
TON = REF205263
TON = float295371On-Time, Side 2tON2V+ = 24V, VOUT2 = 2V
(Note 3)
TON = VCC422534
TON = AGND125145
TON = REF125145
TON = float125145On-Time Tracking
On-time 2, with
respect to on-time 1
(Note 3)
TON = VCC125145
Minimum Off-TimetOFF(Note 3)500ns
Quiescent Supply Current (VCC)ICCFB forced above the regulation point1500µA
Quiescent Supply Current (VDD)IDDFB forced above the regulation point5µA
Quiescent Supply Current (V+)I+Measured at V+70µA
Reference VoltageVREFVCC = 4.5V to 5.5V, no external REF load1.982.02V
Reference Load RegulationIREF = 0 to 50µA0.01V
Overvoltage Trip Threshold
(Fixed-Threshold Mode)
OVP = GND, with respect to FB_ regulation
point, no load112117%
Output Undervoltage ThresholdUVP = VCC, with respect to FB_ regulation
point, no load6575%
Current-Limit Threshold (Fixed)AGND - VCS_, ILIM_ = VCC3565mV
