19-3318; Rev 1; 8/05
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
The on-demand PWM controllers are free running, constant on-time with input feed-forward. This configuration
provides ultra-fast transient response, wide input-output
differential range, low supply current, and tight load-regulation 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 battery 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.
Features
♦ Ultra-High Efficiency
♦ Accurate Current-Limit Option
♦ Quick-PWM™ with 100ns Load-Step Response
♦ 1% VOUT Accuracy over Line and Load
♦ High Output Impedance in Shutdown
♦ Dual Mode™ Fixed 1.8V/1.5V/Adj or 2.5V/Adj Outputs
♦ Adjustable 1V to 5.5V Output Range
♦ 2V to 28V Battery Input Range
♦ 200kHz/300kHz/420kHz/540kHz Nominal Switching
Frequency
♦ Adjustable Overvoltage Protection
♦ 1.7ms Digital Soft-Start
♦ Drives Large Synchronous-Rectifier FETs
♦ Power-Good Window Comparator
♦ 2V ±1% Reference Output
Ordering Information
TEMP RANGE
PIN-PACKAGE
MAX8743EEI
PART
-40°C to +85°C
28 QSOP
MAX8743EEI+
-40°C to +85°C
28 QSOP
+Denotes lead-free package.
Ordering Information continued at end of data sheet.
Minimal Operating Circuit
Applications
Notebook Computers
5V INPUT
CPU Core Supplies
Chipset/RAM Supplies as Low as 1V
1.8V and 2.5V I/O Supplies
OUTPUT1
1.8V
BATTERY
4.5V TO 28V
VDD
V+
VCC
UVP
ILIM1
ILIM2
ON1
ON2
OVP
BST1
BST2
DH1
DH2
LX1
LX2
DL1
DL2
MAX8743EEI
OUTPUT2
2.5V
CS2
TON
CS1
OUT1
PGOOD
OUT2
REF
SKIP
Pin Configurations appear at end of data sheet.
FB2
FB1
GND
Quick-PWM and Dual Mode are trademarks of Maxim Integrated
Products, Inc.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX8743
General Description
The 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 lowvoltage 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 current-sense elements. High output impedance in shutdown eliminates negative output voltages, saving the
cost of a Schottky diode at the output.
MAX8743
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
ABSOLUTE MAXIMUM RATINGS (Note 1)
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
V+ to AGND..............................................................-0.3 to +30V
VCC to AGND............................................................-0.3V to +6V
VDD to 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)
Note 1: For the MAX8743EEI, AGND and PGND refer to a single pin designated GND.
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.
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 otherwise
noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
PWM CONTROLLERS
Input Voltage Range
DC Output Voltage OUT1
(Note 2)
DC Output Voltage OUT2
(Note 2)
V+
VCC/VDD
Battery voltage, V+
VCC, VDD
V+ = 2V to 28V, ILOAD
= 0 to 8A, SKIP = VCC,
+25°C to +85°C
VOUT1
V+ = 2V to 28V, ILOAD
= 0 to 8A, SKIP = VCC,
0°C to +85°C
V+ = 4.5V to 28V,
ILOAD = 0 to 4A,
SKIP = VCC,
+25°C to +85°C
VOUT2
V+ = 4.5V to 28V,
ILOAD = 0 to 4A,
SKIP = VCC,
0°C to +85°C
2
28
4.5
5.5
FB1 to AGND
1.782
1.8
1.818
1.515
FB1 to VCC
1.485
1.5
FB1 to OUT1
0.99
1
1.01
FB1 to AGND
1.773
1.8
1.827
FB1 to VCC
1.477
1.5
1.523
0.985
1
1.015
FB2 to AGND
2.475
2.5
2.525
FB2 to OUT2
0.99
1
1.01
FB2 to AGND
2.463
2.5
2.537
FB2 to OUT2
0.985
1
1.015
5.5
V
0.1
0.15
V
VCC 0.4
V
V
OUT1, OUT2
Dual-Mode Threshold, Low
OVP, FB_
0.05
OVP, ILIM_
VCC 1.5
FB1
OUT_ Input Resistance
FB_ Input-Bias Current
Soft-Start Ramp Time
2
1
1.9
ROUT1
VOUT1 = 1.5V
75
ROUT2
VOUT2 = 2.5V
100
IFB
2.0
2.1
kΩ
-0.1
Zero to full ILIM
V
FB1 to OUT1
Output Voltage Adjust Range
Dual-Mode Threshold, High
V
+0.1
1700
_______________________________________________________________________________________
µA
µs
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
(Circuit of Figure 1, VDD = VCC = 5V, SKIP = AGND, V+ = 15V, TA = 0°C to +85°C, typical values are at +25°C, unless otherwise
noted.)
PARAMETER
On-Time, Side 1
SYMBOL
tON1
On-Time, Side 2
tON2
On-Time Tracking
CONDITIONS
V+ = 24V,
VOUT1 = 2V
(Note 3)
MIN
TYP
MAX
TON = AGND
120
137
153
TON = REF
153
174
195
TON = float
222
247
272
TON = VCC
316
353
390
TON = AGND
160
182
204
V+ = 24V,
VOUT2 = 2V
(Note 3)
TON = REF
205
234
263
TON = float
301
336
371
TON = VCC
432
483
534
On-time 2 with
respect to ontime 1
(Note 3)
TON = AGND
125
135
145
TON = REF
125
135
145
TON = float
125
135
145
TON = VCC
125
135
145
UNITS
ns
ns
%
Minimum Off-Time
tOFF
(Note 3)
400
500
ns
Quiescent Supply Current (VCC)
ICC
FB_ forced above the regulation point
1100
1500
µA
Quiescent Supply Current (VDD)
IDD
FB_ forced above the regulation point