Maxim MAX8743EEI Schematics

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.

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.

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.

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-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

MAX8743

Dual, High-Efficiency, Step-Down

Controller with High Impedance in Shutdown

________________________________________________________________ Maxim Integrated Products 1

19-3318; Rev 1; 8/05

Pin Configurations appear at end of data sheet.

Quick-PWM and Dual Mode are trademarks of Maxim Integrated
Products, Inc.

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 -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.

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 (VCC+ 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

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, VDD= V

CC

= 5V, SKIP = AGND, V+ = 15V, TA= 0°C to +85°C, typical values are at +25°C, unless otherwise

noted.)

PARAMETER

CONDITIONS

UNITS

PWM CONTROLLERS

V+ Battery voltage, V+ 2 28

Input Voltage Range

VCC, V

DD

4.5 5.5

V

FB1 to AGND

1.8

FB1 to V

CC

1.5

V+ = 2V to 28V, I

LOAD

= 0 to 8A, SKIP = VCC,
+25°C to +85°C

FB1 to OUT1

1

FB1 to AGND

1.8

FB1 to V

CC

1.5

DC Output Voltage OUT1
(Note 2)

V+ = 2V to 28V, I

LOAD

= 0 to 8A, SKIP = VCC,
0°C to +85°C

FB1 to OUT1

1

V

FB2 to AGND

2.5

V+ = 4.5V to 28V,
I

LOAD

= 0 to 4A,

SKIP = V

CC

,

+25°C to +85°C

FB2 to OUT2

1

FB2 to AGND

2.5

DC Output Voltage OUT2

(Note 2)

V+ = 4.5V to 28V,
I

LOAD

= 0 to 4A,

SKIP = V

CC

,

0°C to +85°C

FB2 to OUT2

1

V

Output Voltage Adjust Range OUT1, OUT2 1 5.5 V

Dual-Mode Threshold, Low OVP, FB_

0.1

V

OVP, ILIM_

V

CC

-

1.5

V

CC

-

0.4

Dual-Mode Threshold, High

FB1 1.9 2.0 2.1

V

V

OUT1

= 1.5V 75

OUT_ Input Resistance

V

OUT2

= 2.5V 100

kΩ

FB_ Input-Bias Current I

FB

µA

Soft-Start Ramp Time Zero to full ILIM

µs

Note 1: For the MAX8743EEI, AGND and PGND refer to a single pin designated GND.

SYMBOL

MIN TYP MAX

VCC/V

DD

1.782

1.485

V

OUT1

V

OUT2

R

OUT1

R

OUT2

0.99

1.773

1.477

0.985

2.475

0.99

2.463

0.985

0.05

-0.1 +0.1

1700

1.818

1.515

1.01

1.827

1.523

1.015

2.525

1.01

2.537

1.015

0.15

MAX8743

Dual, High-Efficiency, Step-Down

Controller with High Impedance in Shutdown

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VDD= V

CC

= 5V, SKIP = AGND, V+ = 15V, TA= 0°C to +85°C, typical values are at +25°C, unless otherwise

noted.)

PARAMETER

CONDITIONS

UNITS

TON = AGND 120 137

TON = REF 153 174

TON = float 222 247

On-Time, Side 1 t

ON1

V+ = 24V,
V

OUT1

= 2V

(Note 3)

TON = V

CC

316 353

ns

TON = AGND 160 182

TON = REF 205 234

TON = float 301 336

On-Time, Side 2 t

ON2

V+ = 24V,
V

OUT2

= 2V

(Note 3)

TON = V

CC

432 483

ns

TON = AGND 125 135

TON = REF 125 135

TON = float 125 135

On-Time Tracking

On-time 2 with
respect to on­time 1
(Note 3)

TON = V

CC

125 135

%

Minimum Off-Time t

OFF

(Note 3) 400

ns

Quiescent Supply Current (VCC)ICCFB_ forced above the regulation point

µA

Quiescent Supply Current (VDD)IDDFB_ forced above the regulation point <1 5 µA

Quiescent Supply Current (V+) I+ Measured at V+ 25 70 µA

Shutdown Supply Current (VCC) ON1 = ON2 = AGND, OVP = V

CC

<1 5 µA

Shutdown Supply Current (VDD) ON1 = ON2 = AGND <1 5 µA

Shutdown Supply Current (V+)

ON1 = ON2 = AGND, measured at V+,
V

CC

= AGND or 5V

<1 5 µA

Reference Voltage V

REF

V

CC

= 4.5V to 5.5V, no external REF load

2

V

Reference Load Regulation I

REF

= 0 to 50µA

V

REF Sink Current REF in regulation 10 µA

REF Fault Lockout Voltage Falling edge, hysteresis = 40mV 1.6 V

Overvoltage Trip Threshold
(Fixed-Threshold Mode)

OVP = AGND, with respect to error­comparator trip threshold

112 114

%

1V < V

OVP

< 1.8V, external feedback,

measured at FB_ with respect to V

OVP

-28 0

mV

Overvoltage Comparator Offset
(Adjustable-Threshold Mode)

1V < V

OVP

< 1.8V, internal feedback,
measured at OUT_ with respect to OUT_
regulation point

0

%

OVP Input Leakage Current 1V < V

OVP

< 1.8V

<1

nA

Overvoltage Fault Propagation
Delay

FB_ forced 2% above trip threshold 1.5 µs

Output Undervoltage Threshold

UVP = VCC, with respect to error-comparator
trip threshold

65 70 75 %

Output Undervoltage Protection
Blanking Time

From ON_ signal going high 10 30 ms

SYMBOL

MIN TYP MAX

1100 1500

1.98

-3.5

-100

153

195

272

390

204

263

371

534

145

145

145

145

500

2.02

0.01

117

+28

+3.5

+100

MAX8743

Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VDD= V

CC

= 5V, SKIP = AGND, V+ = 15V, TA= 0°C to +85°C, typical values are at +25°C, unless otherwise

noted.)

PARAMETER

CONDITIONS

UNITS

Current-Limit Threshold (Fixed) AGND - VCS_, ILIM_ = V

CC

40 50 60 mV

AGND - VCS_, ILIM_ = 0.5V 40 50 60

Current-Limit Threshold
(Adjustable)

AGND - V

CS

_, ILIM_ = 1V 85 100

mV

ILIM_ Adjustment Range

0.3 2.5 V

Negative Current-Limit Threshold
(Fixed)

V

CS

_ - AGND, ILIM_ = VCC, TA = +25 oC -75 -60

mV

Thermal-Shutdown Threshold Hysteresis = 15oC

o

C

VCC Undervoltage-Lockout
Threshold

Rising edge, hysteresis = 20mV, PWMs
disabled below this level

V

MAX8743EEI 1.5 5 Ω

DH Gate-Driver On-Resistance

(Note 4)

MAX8743ETX 1.5 6 Ω
MAX8743EEI 1.5 5 Ω

DL Gate-Driver On-Resistance

DL, high state
(Note 4)

MAX8743ETX 1.5 6 Ω
MAX8743EEI 0.5 1.7 Ω

DL Gate-Driver On-Resistance

DL, low state
(Note 4)

MAX8743ETX 0.5 2.7 Ω

DH_ Gate-Driver Source/Sink
Current

V

DH

_ = 2.5V, V

BST

_ = VLX_ = 5V 1 A

DL_ Gate-Driver Sink Current VDL_ = 2.5V 3 A

DL_ Gate-Driver Source Current VDL_ = 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

V

V

CC

level

V

CC

-

0.4

Float level

REF level

TON Input Logic Level

AGND level 0.5

V

Logic Input Current TON (AGND or VCC)-3+3µA
Logic Input Current ON_, SKIP, UVP -1 +1 µA

PGOOD Trip Threshold (Lower)

With respect to error-comparator trip
threshold, falling edge

-10

%

PGOOD Trip Threshold (Upper)

With respect to error-comparator trip
threshold, rising edge

%

PGOOD Propagation Delay

Falling edge, FB_ forced 2% below PGOOD
trip threshold

1.5 µs

PGOOD Output Low Voltage I

SINK

= 1mA 0.4 V

PGOOD Leakage Current High state, forced to 5.5V 1 µA

SYMBOL

V

_

ILIM

BST - LX forced to 5V

MIN TYP MAX

+160

4.05 4.40

3.15 3.85

1.65 2.35

-12.5

+7.5 +10 +12.5

115

-45

0.05

-7.5

MAX8743

Dual, High-Efficiency, Step-Down

Controller with High Impedance in Shutdown

_______________________________________________________________________________________ 5

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, VDD= V

CC

= 5V, SKIP = AGND, V+ = 15V, TA= -40°C to +85°C, unless otherwise noted.) (Note 5)

PARAMETER

CONDITIONS

UNITS

PWM CONTROLLERS

V+ Battery voltage, V+ 2 28

Input Voltage Range

VCC, V

DD

4.5 5.5

V

FB1 to V

CC

D C O utp ut V ol tag e, O U T1

V+ = 2V to 28V, SKIP = VCC,
I

LOAD

= 0 to 8A

( N ote 2)

V

D C O utp ut V ol tag e, O U T2

V+ = 2V to 28V, SKIP = VCC,
I

LOAD

= 0 to 4A ( N ote 2)

V

Output Voltage Adjust Range OUT1, OUT2 1.0 5.5 V

Dual-Mode Threshold, Low OVP, FB_

V

OVP, ILIM_

V

CC

-

1.5

V

CC

-

0.4

Dual-Mode Threshold, High

FB_ 1.9 2.1

V

V

OUT1

= 1.5V 75

OUT_ Input Resistance

V

OUT2

= 2.5V

kΩ

FB_ Input Bias Current I

FB

µA

TON = AGND

153

TON = REF

195

TON = float

272

On-Time, Side 1 t

ON1

(Note 3)

TON = V

CC

390

ns

TON = AGND

204

TON = REF

263

TON = float

371

On-Time, Side 2 t

ON2

(Note 3)

TON = V

CC

534

ns

TON = AGND

145

TON = REF

145

TON = float

145

On-Time Tracking

On-time 2, with
respect to on-time 1
(Note 3)

TON = V

CC

145

%

Minimum Off-Time t

OFF

(Note 3) 500 ns

Quiescent Supply Current (VCC)ICCFB forced above the regulation point

µA

Quiescent Supply Current (VDD)IDDFB forced above the regulation point 5 µA

Quiescent Supply Current (V+) I+ Measured at V+ 70 µA

Reference Voltage V

REF

V

CC

= 4.5V to 5.5V, no external REF load

V

Reference Load Regulation I

REF

= 0 to 50µA

V

Overvoltage Trip Threshold
(Fixed-Threshold Mode)

OVP = GND, with respect to FB_ regulation
point, no load

117 %

Output Undervoltage Threshold

UVP = V

CC

, with respect to FB_ regulation

point, no load

65 75 %

Current-Limit Threshold (Fixed) AGND - VCS_, ILIM_ = V

CC

35 65 mV

SYMBOL

VCC/V

DD

MIN TYP MAX

FB1 to AGND 1.773 1.827

V

OUT1

1.477 1.523

FB1 to OUT1 0.985 1.015

V

OUT2

FB2 to AGND 2.463 2.537

FB2 to OUT2 0.985 1.015

0.05 0.15

R

OUT1

R

OUT2

100

-0.1 +0.1

120

153

217

308

160

205

295

422

125

125

125

125

1.98 2.02

112

V+ = 24V, V

OUT1

= 2V

V+ = 24V, V

OUT2

= 2V

1500

0.01

MAX8743

Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown

6 _______________________________________________________________________________________

0

0.01 1010.1

300

350

400

200

250

100

150

50

MAX8743 toc01

LOAD CURRENT (A)

FREQUENCY (kHz)

FREQUENCY vs. LOAD CURRENT

OUT1, SKIP = V

CC

OUT2, SKIP = V

CC

OUT1, SKIP = GND

OUT2, SKIP = GND

0

50

100

150

200

250

300

350

400

481216 20 24

MAX8743 toc02

INPUT VOLTAGE (V)

FREQUENCY (kHz)

FREQUENCY vs. INPUT VOLTAGE

(TON = FLOAT, SKIP = V

CC

)

OUT1

OUT2

I

OUT1

= 8A

I

OUT2

= 4A

__________________________________________Typical Operating Characteristics

(Circuit of Figure 1, components from Table 1, VIN= 15V, SKIP = GND, TON = unconnected, TA= +25°C, unless otherwise noted.)

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VDD= V

CC

= 5V, SKIP = AGND, V+ = 15V, TA= -40°C to +85°C, unless otherwise noted.) (Note 5)

Note 2: When the inductor is in continuous conduction, the output voltage will have a DC regulation level higher than the error-compara-

tor threshold by 50% of the output voltage ripple. In discontinuous conduction (SKIP = AGND, light load), the output voltage
has a DC regulation higher than the error-comparator threshold by approximately 1.5% due to slope compensation.

Note 3: On-time and off-time specifications are measured from the 50% point to the 50% point at DH_ with LX_ = GND, BST_ = 5V,

and a 250pF capacitor connected from DH_ to LX_. Actual in-circuit times may differ due to MOSFET switching speeds.

Note 4: Production testing limitations due to package handling require relaxed maximum on-resistance specifications for the QFN

package. The MAX8743EEI and MAX8743ETX contain the same die, and the QFN package imposes no additional resis­tance in-circuit.

Note 5: Specifications to -40°C are guaranteed by design, not production tested.

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

AGND - VCS_, ILIM_ = 0.5V 35 65

Current-Limit Threshold
(Adjustable)

AGND - V

CS

_, ILIM_ = 1V 80 120

mV

VCC Undervoltage-Lockout
Threshold

Rising edge, hysteresis = 20mV, PWMs
disabled below this level

V

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

V

TON (AGND or VCC)-3+3

Logic Input Current

ON_, SKIP, UVP -1 +1

µA

4.05 4.40

0.05

MAX8743

Dual, High-Efficiency, Step-Down

Controller with High Impedance in Shutdown

_______________________________________________________________________________________ 7

0

4.5

3.0

1.5

6.0

7.5

9.0

10.5

12.0

13.5

15.0

51510 20 25 30

MAX8743 toc03

INPUT VOLTAGE V+ (V)

SUPPLY CURRENT (mA)

NO-LOAD SUPPLY CURRENT

vs. INPUT VOLTAGE (SKIP = V

CC

)

I

CC

VCC = VDD = 5V

I

DD

I+ (25µA TYP)

0

100

200

300

400

500

600

700

800

900

1000

1100

MAX8743 toc04

INPUT VOLTAGE V+ (V)

SUPPLY CURRENT (µA)

51015202530

NO-LOAD SUPPLY CURRENT

vs. INPUT VOLTAGE (SKIP = GND)

VCC = VDD = 5V

IDD (600nA TYP)

I

CC

I+

10

0.01 1010.1

60

70

80

90

100

40

50

20

30

MAX8743 toc05

LOAD CURRENT (A)

EFFICIENCY (%)

EFFICIENCY vs. LOAD CURRENT

(8A COMPONENTS, SKIP = V

CC

)

V+ = 7V

V+ = 20V

V+ = 12V

OUT1 = 1.8V

50

0.01 1010.1

75

80

85

90

95

100

65

70

55

60

MAX8743 toc06

LOAD CURRENT (A)

EFFICIENCY (%)

EFFICIENCY vs. LOAD CURRENT
(8A COMPONENTS, SKIP = GND)

V+ = 7V

V+ = 20V

OUT1 = 1.8V

V+ = 12V

10

50
30

70

90

110

130

150

170

190

210

230

250

0 0.5 1.0 1.5 2.0 2.5

CURRENT-LIMIT TRIP POINT

vs. ILIM VOLTAGE

MAX8743 toc09

ILIM VOLTAGE (V)

CURRENT-LIMIT TRIP POINT (mV)

10

0.01 1010.1

60

70

80

90

100

40

50

20

30

MAX8743 toc07

LOAD CURRENT (A)

EFFICIENCY (%)

EFFICIENCY vs. LOAD CURRENT

(4A COMPONENTS, SKIP = V

CC

)

V+ = 7V

V+ = 20V

V+ = 12V

OUT2 = 2.5V

80

75

0.01 1010.1

95

100

90

85

MAX8743 toc08

LOAD CURRENT (A)

EFFICIENCY (%)

EFFICIENCY vs. LOAD CURRENT
(4A COMPONENTS, SKIP = GND)

V+ = 7V

V+ = 12V

V+ = 20V

OUT2 = 2.5V

1.0

1.2

1.1

1.4

1.3

1.6

1.5

1.7

1.9

1.8

2.0

1.0 1.2 1.31.1 1.4 1.5 1.6 1.7 1.8

MAX8743 toc10

OVP VOLTAGE (V)

NORMALIZED THRESHOLD (V)

NORMALIZED OVERVOLTAGE PROTECTION

THRESHOLD vs. OVP VOLTAGE

MAX8743 toc11

I

OUT2

2A/div

20µs/div

V

OUT2

100mV/div

LOAD-TRANSIENT RESPONSE

(4A COMPONENTS, PWM MODE, V

OUT2

= 2.5V)

Typical Operating Characteristics (continued)

(Circuit of Figure 1, components from Table 1, VIN= 15V, SKIP = GND, TON = unconnected, TA= +25°C, unless otherwise noted.)

MAX8743

Dual, High-Efficiency, Step-Down
Controller with High Impedance in Shutdown

8 _______________________________________________________________________________________

MAX8743 toc13

400µs/div

V

OUT2

1V/div

2.5V

0V

0V

0V

0A

ON2
5V/div

PGOOD
5V/div

I

LX2

1A/div

STARTUP WAVEFORM (V

OUT2

)

R

OUT2

= 2.5Ω

MAX8743 toc14

400µs/div

V

OUT2

1V/div

2.5V

0V

0V

0V

0V

ON2
5V/div

PGOOD
5V/div

DL2
5V/div

SHUTDOWN WAVEFORM (V

OUT2

)

R

OUT2

= 2.5Ω

Typical Operating Characteristics (continued)

(Circuit of Figure 1, components from Table 1, VIN= 15V, SKIP = GND, TON = unconnected, TA= +25°C, unless otherwise noted.)

PIN

QSOP

NAME

FUNCTION

132OUT1

Output Voltage Connection for the OUT1 PWM. Connect directly to the junction of the external
inductor and output filter capacitors. OUT1 senses the output voltage to determine the on-time
and also serves as the feedback input in fixed-output modes.

233FB1

Feed b ack Inp ut for O U T1. C onnect to G N D for 1.8V fi xed outp ut or to V

C C

for 1.5V fi xed outp ut, or

connect to a r esi stor - d i vi d er netw or k fr om O U T1 for an ad j ustab l e outp ut b etw een 1V and 5.5V .

334ILIM1

Current-Limit Threshold Adjustment for OUT1. The current-limit threshold at CS1 is 0.1 times the
voltage at ILIM1. Connect a resistor-divider network from REF to set the current-limit threshold
between 25mV and 250mV (with 0.25V to 2.5V at ILIM). Connect to V

CC

to assert 50mV default

current-limit threshold.

435 V+

Battery Voltage-Sense Connection. Connect to input power source. V+ is only used to adjust the
DH_ on-time for pseudofixed-frequency operation.

On-Time Selection Control Input. This four-level input pin sets the DH_ on-time to determine the
operating frequency.

TON FREQUENCY (OUT1) (kHz)

FREQUENCY (OUT2) (kHz)

AGND 620 460

REF 485 355

Open 345 255

51TON

V

CC

235 170

62SKIP

Pulse-Skipping Control Input. Connect to V

CC

for low-noise forced-PWM mode. Connect to AGND

to enable pulse-skipping operation.

Pin Description

MAX8743 toc12

I

OUT1

5A/div

20µs/div

V

OUT1

100mV/div

LOAD-TRANSIENT RESPONSE

(8A COMPONENTS, PWM MODE, V

OUT1

= 1.8V)

TQFN

MAX8743

Dual, High-Efficiency, Step-Down

Controller with High Impedance in Shutdown

_______________________________________________________________________________________ 9

Pin Description (continued)

PIN

QSOP

NAME

FUNCTION

73

Power-Good Open-Drain Output. PGOOD is low when either output voltage is more than 10%
above or below the normal regulation point, and during the 1.7ms soft-start time.

84OVP

Overvoltage Protection Threshold. An overvoltage fault occurs if the voltage on FB1 or FB2 is
greater than the programmed overvoltage trip threshold. Adjustment range is 1V (100%) to 1.8V
(180%). Connect OVP to GND to set the default overvoltage threshold of 114% of nominal.
Connect to V

CC

to disable OVP and clear the OVP latch.

95UVP

U nd er vol tag e P r otecti on Thr eshol d . An und er vol tag e faul t occur s i f the vol tag e on FB1 or FB2 i s l ess
than the und er vol tag e tr i p thr eshol d ( 70% of nom i nal ) . C onnect U V P to V

C C

to enab l e und er vol tag e

p r otecti on. C onnect to GN D to d i sab l e und er vo l tag e p r otecti on and cl ear the U V P l atch.

10 7 REF

+2.0V Reference Voltage Output. Bypass to GND with 0.22µF (min) capacitor. Can supply 50µA
for external loads.

11 8 ON1 OU T1 ON /OFF C ontr ol Inp ut. C onnect to AGN D to tur n OU T1 off. C onnect to V

C C

to tur n O U T1 on.

12 11 ON2 OU T2 ON /OFF C ontr ol Inp ut. C onnect to AGN D to tur n OU T2 off. C onnect to V

C C

to tur n O U T2 on.

13 12 ILIM2

Current-Limit Threshold Adjustment for OUT2. The current-limit threshold at CS2 is 0.1 times the
voltage at ILIM2. Connect a resistor-divider network from REF to set the current-limit threshold
between 25mV and 250mV (with 0.25V to 2.5V at ILIM). Connect to V

CC

to assert 50mV default

current-limit threshold.

14 13 FB2

Feedback Input for OUT2. Connect to GND for 2.5V fixed output, or connect to a resistor-divider
network from OUT2 for an adjustable output between 1V and 5.5V.

15 14 OUT2

Output Voltage Connection for the OUT2 PWM. Connect directly to the junction of the external
inductor and output filter capacitors. OUT2 senses the output voltage to determine the on-time
and also serves as the feedback input in fixed-output modes.

16 15 CS2

Current-Sense Input for OUT2. CS2 is the input to the current-limiting circuitry for valley current
limiting. For lowest cost and highest efficiency, connect to LX2. For highest accuracy, use a sense
resistor. See the Current-Limit Circuit (ILIM_) section.

17 16 LX2

External Inductor Connection for OUT2. Connect to the switched side of the inductor. LX2 serves
as the internal lower supply voltage rail for the DH2 high-side gate driver.

18 18 DH2 High-Side Gate-Driver Output for OUT2. Swings from LX2 to BST2.

19 19 BST2

Boost Flying Capacitor Connection for OUT2. Connect to an external capacitor and diode
according to the standard application circuit in Figure 1. See the MOSFET Gate Drivers (DH_,
DL_) section.

20 20 DL2 Low-Side Gate-Driver Output for OUT2. DL2 swings from PGND to VDD.

21 21 V

DD

Supply Input for the DL Gate Drivers. Connect to system supply voltage, +4.5V to +5.5V. Bypass
to PGND with a low-ESR 4.7µF capacitor.

22 22 V

CC

Analog Supply Input. Connect to system supply voltage, +4.5V to +5.5V, with a 20Ω series
resistor. Bypass to AGND with a 1µF capacitor.

23 — GND Ground. Combined analog and power ground. Serves as negative input for CS_ amplifiers.

TQFN

PGOOD