19-3318; Rev 1; 8/05
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
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 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.
♦
Ultra-High Efficiency
♦
Accurate Current-Limit Option
♦
Quick-PWM™ with 100ns Load-Step Response
♦
1% V
OUT
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
Features
Ordering Information
PART
MAX8743EEI
MAX8743EEI+
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
28 QSOP
28 QSOP
+Denotes
lead-free package.
Ordering Information continued at end of data sheet.
Minimal Operating Circuit
Applications
Notebook Computers
CPU Core Supplies
Chipset/RAM Supplies as Low as 1V
1.8V and 2.5V I/O Supplies
5V INPUT
V
DD
V
CC
ILIM1
ILIM2
ON1
ON2
BST1
OUTPUT1
1.8V
DH1
LX1
DL1
V+
UVP
OVP
BATTERY
4.5V TO 28V
MAX8743EEI
BST2
DH2
LX2
DL2
OUTPUT2
2.5V
CS2
TON
CS1
OUT1
PGOOD
OUT2
REF
SKIP
Pin Configurations appear at end of data sheet.
Quick-PWM and Dual Mode are trademarks of Maxim Integrated
Products, Inc.
FB1
GND
FB2
________________________________________________________________
Maxim Integrated Products
1
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.
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
MAX8743
ABSOLUTE MAXIMUM RATINGS (Note 1)
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
= +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
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, V
DD
= V
CC
= 5V,
SKIP
= AGND, V+ = 15V,
T
A
= 0°C to +85°C,
typical values are at +25°C, unless otherwise
noted.)
PARAMETER
PWM CONTROLLERS
Input Voltage Range
V+
V
CC
/V
DD
Battery voltage, V+
V
CC
, V
DD
V+ = 2V to 28V, I
LOAD
= 0 to 8A,
SKIP
= V
CC
,
+25°C to +85°C
V
OUT1
V+ = 2V to 28V, I
LOAD
= 0 to 8A,
SKIP
= V
CC
,
0°C to +85°C
V+ = 4.5V to 28V,
I
LOAD
= 0 to 4A,
SKIP
= V
CC
,
+25°C to +85°C
V
OUT2
V+ = 4.5V to 28V,
I
LOAD
= 0 to 4A,
SKIP
= V
CC
,
0°C to +85°C
OUT1, OUT2
OVP, FB_
OVP, ILIM_
FB1
OUT_ Input Resistance
FB_ Input-Bias Current
Soft-Start Ramp Time
R
OUT1
R
OUT2
I
FB
Zero to full ILIM
V
OUT1
= 1.5V
V
OUT2
= 2.5V
FB1 to AGND
FB1 to V
CC
FB1 to OUT1
FB1 to AGND
FB1 to V
CC
FB1 to OUT1
FB2 to AGND
FB2 to OUT2
FB2 to AGND
FB2 to OUT2
2
4.5
1.782
1.485
0.99
1.773
1.477
0.985
2.475
0.99
2.463
0.985
1
0.05
V
CC
-
1.5
1.9
75
100
-0.1
1700
+0.1
2.0
0.1
1.8
1.5
1
1.8
1.5
1
2.5
1
2.5
1
28
5.5
1.818
1.515
1.01
1.827
1.523
1.015
2.525
1.01
V
2.537
1.015
5.5
0.15
V
CC
-
0.4
2.1
kΩ
µA
µs
V
V
V
V
V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DC Output Voltage OUT1
(Note 2)
DC Output Voltage OUT2
(Note 2)
Output Voltage Adjust Range
Dual-Mode Threshold, Low
Dual-Mode Threshold, High
2
_______________________________________________________________________________________
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
MAX8743
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
DD
= V
CC
= 5V,
SKIP
= AGND, V+ = 15V,
T
A
= 0°C to +85°C,
typical values are at +25°C, unless otherwise
noted.)
PARAMETER
SYMBOL
V+ = 24V,
V
OUT1
= 2V
(Note 3)
CONDITIONS
TON = AGND
On-Time, Side 1
t
ON1
TON = REF
TON = float
TON = V
CC
TON = AGND
On-Time, Side 2
t
ON2
V+ = 24V,
V
OUT2
= 2V
(Note 3)
On-time 2 with
respect to on-
time 1
(Note 3)
t
OFF
I
CC
I
DD
I+
(Note 3)
FB_ forced above the regulation point
FB_ forced above the regulation point
Measured at V+
ON1 = ON2 = AGND, OVP = V
CC
ON1 = ON2 = AGND
ON1 = ON2 = AGND, measured at V+,
V
CC
= AGND or 5V
V
REF
V
CC
= 4.5V to 5.5V, no external REF load
I
REF
= 0 to 50µA
REF in regulation
Falling edge, hysteresis = 40mV
OVP = AGND, with respect to error-
comparator trip threshold
1V < V
OVP
< 1.8V, external feedback,
measured at FB_ with respect to V
OVP
Overvoltage Comparator Offset
(Adjustable-Threshold Mode)
1V < V
OVP
< 1.8V, internal feedback,
measured at OUT_ with respect to OUT_
regulation point
1V < V
OVP
< 1.8V
FB_ forced 2% above trip threshold
UVP = V
CC
, with respect to error-comparator
trip threshold
From ON_ signal going high
65
10
112
-28
10
1.6
114
0
117
+28
1.98
TON = REF
TON = float
TON = V
CC
TON = AGND
TON = REF
TON = float
TON = V
CC
MIN
120
153
222
316
160
205
301
432
125
125
125
125
TYP
137
174
247
353
182
234
336
483
135
135
135
135
400
1100
<1
25
<1
<1
<1
2
MAX
153
195
272
390
204
263
371
534
145
145
145
145
500
1500
5
70
5
5
5
2.02
0.01
ns
µA
µA
µA
µA
µA
µA
V
V
µA
V
%
mV
%
ns
ns
UNITS
On-Time Tracking
Minimum Off-Time
Quiescent Supply Current (V
CC
)
Quiescent Supply Current (V
DD
)
Quiescent Supply Current (V+)
Shutdown Supply Current (V
CC
)
Shutdown Supply Current (V
DD
)
Shutdown Supply Current (V+)
Reference Voltage
Reference Load Regulation
REF Sink Current
REF Fault Lockout Voltage
Overvoltage Trip Threshold
(Fixed-Threshold Mode)
-3.5
-100
0
<1
1.5
70
+3.5
+100
%
nA
µs
OVP Input Leakage Current
Overvoltage Fault Propagation
Delay
Output Undervoltage Threshold
Output Undervoltage Protection
Blanking Time
75
30
%
ms
_______________________________________________________________________________________
3
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
MAX8743
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
DD
= V
CC
= 5V,
SKIP
= AGND, V+ = 15V,
T
A
= 0°C to +85°C,
typical values are at +25°C, unless otherwise
noted.)
PARAMETER
Current-Limit Threshold (Fixed)
Current-Limit Threshold
(Adjustable)
ILIM_ Adjustment Range
Negative Current-Limit Threshold
(Fixed)
Thermal-Shutdown Threshold
V
CC
Undervoltage-Lockout
Threshold
DH Gate-Driver On-Resistance
DL Gate-Driver On-Resistance
DL Gate-Driver On-Resistance
DH_ Gate-Driver Source/Sink
Current
DL_ Gate-Driver Sink Current
DL_ Gate-Driver Source Current
Logic Input High Voltage
V
IH
V
ILIM
_
V
CS
_ - AGND, ILIM_ = V
CC
, T
A
= +25
o
C
Hysteresis = 15
o
C
Rising edge, hysteresis = 20mV, PWMs
disabled below this level
BST - LX forced to 5V
(Note 4)
DL, high state
(Note 4)
DL, low state
(Note 4)
MAX8743EEI
MAX8743ETX
MAX8743EEI
MAX8743ETX
MAX8743EEI
MAX8743ETX
4.05
1.5
1.5
1.5
1.5
0.5
0.5
1
3
1
2.4
V
CC
-
0.4
0.8
0.05
V
CC
-
0.4
3.15
1.65
-3
-1
-12.5
+7.5
-10
+10
1.5
0.4
1
3.85
2.35
0.5
+3
+1
-7.5
+12.5
µA
µA
%
%
µs
V
µA
V
V
SYMBOL
CONDITIONS
AGND - V
CS
_, ILIM_ = V
CC
AGND - V
CS
_, ILIM_ = 0.5V
AGND - V
CS
_, ILIM_ = 1V
MIN
40
40
85
0.3
-75
-60
+160
4.40
5
6
5
6
1.7
2.7
TYP
50
50
100
MAX
60
60
115
2.5
-45
UNITS
mV
mV
V
mV
o
C
V
Ω
Ω
Ω
Ω
Ω
Ω
A
A
A
V
DH
_ = 2.5V, V
BST
_ = V
LX
_ = 5V
V
DL
_ = 2.5V
V
DL
_ = 2.5V
ON_,
SKIP
UVP
ON_,
SKIP
UVP
V
CC
level
Logic Input Low Voltage
V
IL
V
TON Input Logic Level
Float level
REF level
AGND level
Logic Input Current
Logic Input Current
PGOOD Trip Threshold (Lower)
PGOOD Trip Threshold (Upper)
PGOOD Propagation Delay
PGOOD Output Low Voltage
PGOOD Leakage Current
TON (AGND or V
CC
)
ON_,
SKIP,
UVP
With respect to error-comparator trip
threshold, falling edge
With respect to error-comparator trip
threshold, rising edge
Falling edge, FB_ forced 2% below PGOOD
trip threshold
I
SINK
= 1mA
High state, forced to 5.5V
4
_______________________________________________________________________________________
Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V
DD
= V
CC
= 5V,
SKIP
= AGND, V+ = 15V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 5)
PARAMETER
PWM CONTROLLERS
Input Voltage Range
V+
V
CC
/V
DD
V
OUT1
Battery voltage, V+
V
CC
, V
DD
V+ = 2V to 28V,
SKIP
= V
CC
,
I
LOAD
= 0 to 8A
(Note 2)
V+ = 2V to 28V,
SKIP
= V
CC
,
I
LOAD
= 0 to 4A (Note 2)
OUT1, OUT2
OVP, FB_
OVP, ILIM_
FB_
OUT_ Input Resistance
FB_ Input Bias Current
R
OUT1
R
OUT2
I
FB
TON = AGND
On-Time, Side 1
t
ON1
V+ = 24V, V
OUT1
= 2V
(Note 3)
TON = REF
TON = float
TON = V
CC
TON = AGND
On-Time, Side 2
t
ON2
V+ = 24V, V
OUT2
= 2V
(Note 3)
TON = REF
TON = float
TON = V
CC
TON = AGND
On-Time Tracking
On-time 2, with
respect to on-time 1
(Note 3)
t
OFF
I
CC
I
DD
I+
V
REF
(Note 3)
FB forced above the regulation point
FB forced above the regulation point
Measured at V+
V
CC
= 4.5V to 5.5V, no external REF load
I
REF
= 0 to 50µA
OVP = GND, with respect to FB_ regulation
point, no load
UVP = V
CC
, with respect to FB_ regulation
point, no load
AGND - V
CS
_, ILIM_ = V
CC
112
65
35
1.98
TON = REF
TON = float
TON = V
CC
Minimum Off-Time
Quiescent Supply Current (V
CC
)
Quiescent Supply Current (V
DD
)
Quiescent Supply Current (V+)
Reference Voltage
Reference Load Regulation
Overvoltage Trip Threshold
(Fixed-Threshold Mode)
Output Undervoltage Threshold
Current-Limit Threshold (Fixed)
V
OUT1
= 1.5V
V
OUT2
= 2.5V
FB1 to AGND
FB1 to V
CC
FB1 to OUT1
FB2 to AGND
FB2 to OUT2
2
4.5
1.773
1.477
0.985
2.463
0.985
1.0
0.05
V
CC
-
1.5
1.9
75
100
-0.1
120
153
217
308
160
205
295
422
125
125
125
125
+0.1
153
195
272
390
204
263
371
534
145
145
145
145
500
1500
5
70
2.02
0.01
117
75
65
ns
µA
µA
µA
V
V
%
%
mV
%
ns
ns
28
5.5
1.827
1.523
1.015
2.537
1.015
5.5
0.15
V
CC
-
0.4
2.1
kΩ
µA
V
V
V
V
V
V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8743
DC Output Voltage, OUT1
DC Output Voltage, OUT2
Output Voltage Adjust Range
Dual-Mode Threshold, Low
Dual-Mode Threshold, High
V
OUT2
_______________________________________________________________________________________
5
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