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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 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.
Applications
Notebook Computers
CPU Core Supplies
Chipset/RAM Supplies as Low as 1V
1.8V and 2.5V I/O Supplies
Features
Ultra-High Efficiency
Accurate Current-Limit Option
Quick-PWMTM with 100ns Load-Step Response
1% V
OUT
Accuracy over Line and Load
High Output Impedance in Shutdown
Dual ModeTM 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
MAX8743
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
________________________________________________________________ Maxim Integrated Products
1
19-3318; Rev 0; 6/04
Pin Configurations appear at end of data sheet.
Quick-PWM and Dual Mode are trademarks of Maxim Integrated
Products, Inc.
V
CC
OUTPUT1
1.8V
BATTERY
4.5V TO 28V
ILIM1
ON2
DL1
TON
OUT1
LX1
DH1
FB1
GND
V
DD
BST1
ILIM2
ON1
REF
DL2
CS2
OUT2
LX2
DH2
FB2
V+
BST2
SKIP
5V INPUT
PGOOD
OUTPUT2
2.5V
MAX8743EEI
UVP
OVP
CS1
Minimal Operating Circuit
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX8743EEI
-40C to +85C
28 QSOP
MAX8743ETX
-40C to +85C
36 Thin QFN
6mm x 6mm
MAX8743
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
2
_______________________________________________________________________________________
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
V
CC
to AGND............................................................-0.3V to +6V
V
DD
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 (V
CC
+ 0.3V)
DL_ to PGND ..............................................-0.3V to (V
DD
+ 0.3V)
BST_ to AGND........................................................-0.3V to +36V
CS_ to AGND.............................................................-6V to +30V
DH1 to LX1 ..............................................-0.3V to (V
BST1
+ 0.3V)
LX_ to BST_ ..............................................................-6V to +0.3V
DH2 to LX2 ..............................................-0.3V to (V
BST2
+ 0.3V)
REF Short Circuit to GND ...........................................Continuous
Continuous Power Dissipation (T
A
= +70C)
28-Pin QSOP (derate 10.8mW/C above +70C)........860mW
36-Pin 6mm
6mm Thin QFN
(derate 26.3mW/C above +70C) .............................2105mW
Operating Temperature Range ...........................-40C to +85C
Junction Temperature ......................................................+150C
Storage Temperature Range .............................-65C to +150C
Lead Temperature (soldering, 10s) .................................+300C
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V
DD
= V
CC
= 5V, SKIP = AGND, V+ = 15V, T
A
= 0C to +85C, typical values are at +25C, unless otherwise
noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
PWM CONTROLLERS
V+
Battery voltage, V+
2
28
Input Voltage Range
V
CC
/V
DD
V
CC
, V
DD
4.5
5.5
V
FB1 to AGND
1.782
1.8
1.818
FB1 to V
CC
1.485
1.5
1.515
V+ = 2V to 28V, I
LOAD
= 0 to 8A, SKIP = V
CC
,
+25C to +85C
FB1 to OUT1
0.99
1
1.01
FB1 to AGND
1.773
1.8
1.827
FB1 to V
CC
1.477
1.5
1.523
DC Output Voltage OUT1
(Note 2)
V
OUT1
V+ = 2V to 28V, I
LOAD
= 0 to 8A, SKIP = V
CC
,
0C to +85C
FB1 to OUT1
0.985
1
1.015
V
FB2 to AGND
2.475
2.5
2.525
V+ = 4.5V to 28V,
I
LOAD
= 0 to 4A,
SKIP = V
CC
,
+25C to +85C
FB2 to OUT2
0.99
1
1.01
FB2 to AGND
2.463
2.5
2.537
DC Output Voltage OUT2
(Note 2)
V
OUT2
V+ = 4.5V to 28V,
I
LOAD
= 0 to 4A,
SKIP = V
CC
,
0C to +85C
FB2 to OUT2
0.985
1
1.015
V
Output Voltage Adjust Range
OUT1, OUT2
1
5.5
V
Dual-Mode Threshold, Low
OVP, FB_
0.05
0.1
0.15
V
OVP, ILIM_
V
CC
-
1.5
V
CC
-
0.4
Dual-Mode Threshold, High
FB1
1.9
2.0
2.1
V
R
OUT1
V
OUT1
= 1.5V
75
OUT_ Input Resistance
R
OUT2
V
OUT2
= 2.5V
100
k
FB_ Input-Bias Current
I
FB
-0.1
+0.1
A
Soft-Start Ramp Time
Zero to full ILIM
1700
s
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
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
DD
= V
CC
= 5V, SKIP = AGND, V+ = 15V, T
A
= 0C to +85C, typical values are at +25C, unless otherwise
noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
TON = AGND
120
137
153
TON = REF
153
174
195
TON = float
222
247
272
On-Time, Side 1
t
ON1
V+ = 24V,
V
OUT1
= 2V
(Note 3)
TON = V
CC
316
353
390
ns
TON = AGND
160
182
204
TON = REF
205
234
263
TON = float
301
336
371
On-Time, Side 2
t
ON2
V+ = 24V,
V
OUT2
= 2V
(Note 3)
TON = V
CC
432
483
534
ns
TON = AGND
125
135
145
TON = REF
125
135
145
TON = float
125
135
145
On-Time Tracking
On-time 2 with
respect to on-
time 1
(Note 3)
TON = V
CC
125
135
145
%
Minimum Off-Time
t
OFF
(Note 3)
400
500
ns
Quiescent Supply Current (V
CC
)
I
CC
FB_ forced above the regulation point
1100
1500
A
Quiescent Supply Current (V
DD
)
I
DD
FB_ forced above the regulation point
<1
5
A
Quiescent Supply Current (V+)
I+
Measured at V+
25
70
A
Shutdown Supply Current (V
CC
)
ON1 = ON2 = AGND, OVP = V
CC
<1
5
A
Shutdown Supply Current (V
DD
)
ON1 = ON2 = AGND
<1
5
A
Shutdown Supply Current (V+)
ON1 = ON2 = AGND, measured at V+,
V
CC
= AGND or 5V
<1
5
A
Reference Voltage
V
REF
V
CC
= 4.5V to 5.5V, no external REF load
1.98
2
2.02
V
Reference Load Regulation
I
REF
= 0 to 50A
0.01
V
REF Sink Current
REF in regulation
10
A
REF Fault Lockout Voltage
Falling edge, hysteresis = 40mV
1.6
V
Overvoltage Trip Threshold
(Fixed-Threshold Mode)
OVP = AGND, with respect to error-
comparator trip threshold
112
114
117
%
1V < V
OVP
< 1.8V, external feedback,
measured at FB_ with respect to V
OVP
-28
0
+28
mV
Overvoltage Comparator Offset
(Adjustable-Threshold Mode)
1V < V
OVP
< 1.8V, internal feedback,
measured at OUT_ with respect to OUT_
regulation point
-3.5
0
+3.5
%
OVP Input Leakage Current
1V < V
OVP
< 1.8V
-100
<1
+100
nA
Overvoltage Fault Propagation
Delay
FB_ forced 2% above trip threshold
1.5
s
Output Undervoltage Threshold
UVP = V
CC
, with respect to error-comparator
trip threshold
65
70
75
%
Output Undervoltage Protection
Blanking Time
From ON_ signal going high
10
30
ms
MAX8743
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
4
_______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
DD
= V
CC
= 5V, SKIP = AGND, V+ = 15V, T
A
= 0C to +85C, typical values are at +25C, unless otherwise
noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Current-Limit Threshold (Fixed)
AGND - V
CS
_, ILIM_ = V
CC
40
50
60
mV
AGND - V
CS
_, ILIM_ = 0.5V
40
50
60
Current-Limit Threshold
(Adjustable)
AGND - V
CS
_, ILIM_ = 1V
85
100
115
mV
ILIM_ Adjustment Range
V
ILIM
_
0.3
2.5
V
Negative Current-Limit Threshold
(Fixed)
V
CS
_ - AGND, ILIM_ = V
CC
, T
A
= +25
o
C
-75
-60
-45
mV
Thermal-Shutdown Threshold
Hysteresis = 15
o
C
+160
o
C
V
CC
Undervoltage-Lockout
Threshold
Rising edge, hysteresis = 20mV, PWMs
disabled below this level
4.05
4.40
V
MAX8743EEI
1.5
5
DH Gate-Driver On-Resistance
BST - LX forced to 5V
(Note 4)
MAX8743ETX
1.5
6
MAX8743EEI
1.5
5
DL Gate-Driver On-Resistance
DL, high state
(Note 4)
MAX8743ETX
1.5
6
MAX8743EEI
0.5
1.7
DL Gate-Driver On-Resistance
DL, low state
(Note 4)
MAX8743ETX
0.5
2.7
DH_ Gate-Driver Source/Sink
Current
V
DH
_ = 2.5V, V
BST
_ = V
LX
_ = 5V
1
A
DL_ Gate-Driver Sink Current
V
DL
_ = 2.5V
3
A
DL_ Gate-Driver Source Current
V
DL
_ = 2.5V
1
A
ON_, SKIP
2.4
Logic Input High Voltage
V
IH
UVP
V
CC
-
0.4
V
ON_, SKIP
0.8
Logic Input Low Voltage
V
IL
UVP
0.05
V
V
CC
level
V
CC
-
0.4
Float level
3.15
3.85
REF level
1.65
2.35
TON Input Logic Level
AGND level
0.5
V
Logic Input Current
TON (AGND or V
CC
)
-3
+3
A
Logic Input Current
ON_, SKIP, UVP
-1
+1
A
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 Delay
Falling edge, FB_ forced 2% below PGOOD
trip threshold
1.5
s
PGOOD Output Low Voltage
I
SINK
= 1mA
0.4
V
PGOOD Leakage Current
High state, forced to 5.5V
1
A
MAX8743
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
_______________________________________________________________________________________
5
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V
DD
= V
CC
= 5V, SKIP = AGND, V+ = 15V, T
A
= -40C to +85C, unless otherwise noted.) (Note 5)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
PWM CONTROLLERS
V+
Battery voltage, V+
2
28
Input Voltage Range
V
CC
/V
DD
V
CC
, V
DD
4.5
5.5
V
FB1 to AGND
1.773
1.827
FB1 to V
CC
1.477
1.523
D C O utp ut V ol tag e, O U T1
V
OUT1
V+ = 2V to 28V, SKIP = V
CC
,
I
LOAD
= 0 to 8A
( N ote 2)
FB1 to OUT1
0.985
1.015
V
FB2 to AGND
2.463
2.537
D C O utp ut V ol tag e, O U T2
V
OUT2
V+ = 2V to 28V, SKIP = V
CC
,
I
LOAD
= 0 to 4A ( N ote 2)
FB2 to OUT2
0.985
1.015
V
Output Voltage Adjust Range
OUT1, OUT2
1.0
5.5
V
Dual-Mode Threshold, Low
OVP, FB_
0.05
0.15
V
OVP, ILIM_
V
CC
-
1.5
V
CC
-
0.4
Dual-Mode Threshold, High
FB_
1.9
2.1
V
R
OUT1
V
OUT1
= 1.5V
75
OUT_ Input Resistance
R
OUT2
V
OUT2
= 2.5V
100
k
FB_ Input Bias Current
I
FB
-0.1
+0.1
A
TON = AGND
120
153
TON = REF
153
195
TON = float
217
272
On-Time, Side 1
t
ON1
V+ = 24V, V
OUT1
= 2V
(Note 3)
TON = V
CC
308
390
ns
TON = AGND
160
204
TON = REF
205
263
TON = float
295
371
On-Time, Side 2
t
ON2
V+ = 24V, V
OUT2
= 2V
(Note 3)
TON = V
CC
422
534
ns
TON = AGND
125
145
TON = REF
125
145
TON = float
125
145
On-Time Tracking
On-time 2, with
respect to on-time 1
(Note 3)
TON = V
CC
125
145
%
Minimum Off-Time
t
OFF
(Note 3)
500
ns
Quiescent Supply Current (V
CC
)
I
CC
FB forced above the regulation point
1500
A
Quiescent Supply Current (V
DD
)
I
DD
FB forced above the regulation point
5
A
Quiescent Supply Current (V+)
I+
Measured at V+
70
A
Reference Voltage
V
REF
V
CC
= 4.5V to 5.5V, no external REF load
1.98
2.02
V
Reference Load Regulation
I
REF
= 0 to 50A
0.01
V
Overvoltage Trip Threshold
(Fixed-Threshold Mode)
OVP = GND, with respect to FB_ regulation
point, no load
112
117
%
Output Undervoltage Threshold
UVP = V
CC
, with respect to FB_ regulation
point, no load
65
75
%
Current-Limit Threshold (Fixed)
AGND - V
CS
_, ILIM_ = V
CC
35
65
mV
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