MAXIM MAX1954A Technical data

General Description

The MAX1954A synchronous current-mode, pulse­width modulation (PWM) buck controller is pin compati­ble with the popular MAX1954 and is suitable for
applications where cost and size are critical.

The MAX1954A operates from an input voltage range of

3.0V to 13.2V, independent of the IC supply. The output
voltage is adjustable down to 0.8V. The IC operates at
a fixed 300kHz switching frequency and provides up to
25A of output current with efficiency up to 95%. This
controller has excellent transient response resulting in
smaller output capacitance.

The MAX1954A features foldback current limiting that
greatly reduces input current and component power
dissipation during output overload or short-circuit
conditions.

The compensation and shutdown control (COMP) input,
in addition to providing compensation to the error
amplifier, can be pulled low to shut down the converter.
An input undervoltage lockout is provided to ensure
proper operation during power sags to prevent the
external power MOSFETs from overheating. Internal
digital soft-start is included to reduce inrush current
and save an external capacitor.

The MAX1954A is available in a tiny 10-pin µMAX

®

package to minimize PC board space.

Applications

Printers and Scanners

Graphic Cards and Video Cards

PCs and Servers

Microprocessor Cores

Low-Voltage Distributed Power

Telecom/Networks

Features

♦ Current-Mode Controller

♦ Fixed-Frequency PWM

♦ Foldback Current Limit
♦ Output Down to 0.8V with ±1% FB Accuracy

♦ 3.0V to 13.2V Input Voltage

♦ 300kHz Switching Frequency

♦ 25A Output-Current Capability

♦ 93% Efficiency

♦ All-N-Channel-MOSFET Design for Low Cost

♦ No Current-Sense Resistor Needed

♦ Internal Digital Soft-Start

♦ Small 10-Pin µMAX Package

MAX1954A

Low-Cost, Current-Mode PWM Buck

Controller with Foldback Current Limit

________________________________________________________________ Maxim Integrated Products 1

Pin Configuration

19-3154; Rev 1; 5/05

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.

Ordering Information

EVALUATION KIT

AVAILABLE

µMAX is a registered trademark of Maxim Integrated Products, Inc.

+Denotes lead-free package.

PART TEMP RANGE PIN-PACKAGE

MAX1954AEUB -40°C to +85°C 10 µMAX
MAX1954AEUB+ -40°C to +85°C 10 µMAX

TOP VIEW

HSD

COMP

1

2

MAX1954A

3

FB

4

5

µMAX

10

BST

9

LX

8

DH

7

PGNDGND

DLIN

6

MAX1954A

Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

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.

IN, FB to GND...........................................................-0.3V to +6V

LX to BST..................................................................-6V to +0.3V

BST to GND ............................................................-0.3V to +20V

DH to LX................................................... -0.3V to (V

BST

+ 0.3V)

DL, COMP to GND.......................................-0.3V to (V

IN

+ 0.3V)

HSD to GND..............................................................-0.3V to 14V

PGND to GND .......................................................-0.3V to +0.3V

Continuous Power Dissipation (T

A

= +70°C)

10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........444mW

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

(V

IN

= 5V, V

BST

- V

LX

= 5V, TA= 0°C to +85°C, unless otherwise noted.)

PARAMETER CONDITIONS

UNITS

GENERAL

Operating Input Voltage Range

3.0 5.5 V

HSD Voltage Range (Note 1) 3.0

V

Quiescent Supply Current V

FB

= 1.5V 1 2

mA

Standby Supply Current

V

IN

= V

BST

= 5.5V, V

HSD

= 13.2V, LX = unconnected,

COMP = GND

2

mA

Undervoltage-Lockout Trip Level

Falling V

IN

, 50mV (typ) hysteresis 2.5 2.7 2.9 V

DC-DC CONTROLLER
Output-Voltage Adjust Range

(V

OUT

)

Maximum output voltage depends on external components

and maximum duty cycle

0.8 V

ERROR AMPLIFIER
FB Regulation Voltage

%

Transconductance 70

µS

Voltage Gain

V/ V

FB Input Leakage Current V

FB

= 0.9V 50

NA

FB Input Common-Mode Range

V

COMP Output-Voltage Swing

V

Current-Sense Amplifier

Voltage Gain

3.5

V / V

V

FB

= 0.8V

Current-Limit Threshold V

PGND

- V

LX

V

FB

= 0V 21 36 51

mV

OSCILLATOR
Switching Frequency MAX1954A

kHz

Maximum Duty Cycle Measured at DH 89 91 93 %
Minimum Duty Cycle V

COMP

= 1.25V, LX = GND, V

BST

= V

IN

= 3.3V 2.5 3 %

MIN TYP MAX

13.2

-1.0 +0.8 +1.0
110 160
200

500

-0.1

0.80

3.15

+1.5

2.36

3.85

110 135 145

240 300 360

MAX1954A

Low-Cost, Current-Mode PWM Buck

Controller with Foldback Current Limit

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(V

IN

= 5V, V

BST

- V

LX

= 5V, TA= 0°C to +85°C, unless otherwise noted.)

PARAMETER CONDITIONS

MIN

TYP

MAX

UNITS

SOFT-START
Soft-Start Period 3.4 ms
Soft-Start Levels

mV
FET DRIVERS
DH, DL Output Low Voltage I

SINK

= 10mA 0.1 V

DH, DL Output High Voltage I

SOURCE

= 10mA

V

IN

- 0.1V or

V

DH Pullup/Pulldown,
DL Pullup On-Resistance

1.5 3 Ω

DL Pulldown On-Resistance 1 2 Ω
LX, BST, HSD Leakage Current V

BST

= 18.7V, VLX = 13.2V, VIN = 5.5V, V

HSD

= 13.2V 30 µA

THERMAL PROTECTION
Thermal Shutdown Rising temperature, 15°C hysteresis

°C
SHUTDOWN CONTROL
COMP Logic-Level Low 3V < V

IN

< 5.5V

V

COMP Logic-Level High 3V < V

IN

< 5.5V 0.8 V

COMP Pullup Current

µA

ELECTRICAL CHARACTERISTICS

(V

IN

= 5V, V

BST

- V

LX

= 5V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)

PARAMETER CONDITIONS

UNITS

GENERAL

3.0 5.5 V

HSD Voltage Range (Note 1) 3.0

V

Quiescent Supply Current V

FB

= 1.5V 2

mA

Standby Supply Current

V

IN

= V

BST

= 5.5V, V

HSD

= 13.2V, LX = unconnected,

COMP = GND

2

mA

Rising V

IN

3% (typ) hysteresis

V

DC-DC CONTROLLER
Output-Voltage Adjust Range

(V

OUT

)

0.8

V

ERROR AMPLIFIER
FB Regulation Voltage

%

Transconductance 70

µS

FB Input Leakage Current V

FB

= 0.9V

NA

V

COMP Output-Voltage Swing 0.8 2.2 V

V

BS T

- 0.1V

12.5

+160

0.25

100

MIN

MAX

Operating Input Voltage Range

13.2

Undervoltage Lockout Trip Level

FB Input Common-Mode Range

2.50

2.93

0.9 x V

IN

-2.5

-0.1

+1.0

160
500

+1.5

MAX1954A

Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit

4 _______________________________________________________________________________________

Note 1: HSD and IN are externally connected for applications where HSD < 5.5V.
Note 2: Specifications to -40°C are guaranteed by design and not production tested.

ELECTRICAL CHARACTERISTICS (continued)

(V

IN

= 5V, V

BST

- V

LX

= 5V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)

PARAMETER CONDITIONS

UNITS

Current-Sense Amplifier

Voltage Gain

V/V

V

FB

= 0.8V

Current-Limit Threshold V

PGND

- V

LX

, MAX1954A

V

FB

= 0V 21 51

mV

OSCILLATOR
Switching Frequency

kHz

Maximum Duty Cycle Measured at DH 89 93 %
Minimum Duty Cycle V

COMP

= 1.25V, LX = GND, V

BST

= V

IN

= 3.3V 3 %

FET DRIVERS
DH, DL Output Low Voltage I

SINK

= 10mA 0.1 V

DH, DL Output High Voltage I

SOURCE

= 10mA

V

IN

- 0.1V or

V

DH Pullup/Pulldown,
DL Pullup On-Resistance

3 Ω

DL Pulldown On-Resistance 2 Ω
LX, BST, HSD Leakage Current V

BST

= 18.7V, VLX = 13.2V, VIN = 5.5V, V

HSD

= 13.2V 30 µA

SHUTDOWN CONTROL
COMP Logic-Level Low 3V < V

IN

< 5.5V

V

COMP Logic-Level High 3V < V

IN

< 5.5V 0.8 V

COMP Pullup Current

µA

MIN

MAX

V

3.15

110

240

BS T

- 0.1V

3.85

145

360

0.25

100

MAX1954A

Low-Cost, Current-Mode PWM Buck

Controller with Foldback Current Limit

_______________________________________________________________________________________ 5

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

EFFICIENCY

vs. LOAD CURRENT

MAX1954A toc01

LOAD CURRENT (A)

EFFICIENCY (%)

100

40

50

60

70

80

90

0.1 1 10

V

OUT

= 2.5V

VIN = V

HSD

= 5V

V

OUT

= 1.5V

2.60

2.55

2.50

2.45

2.40
021 345

OUTPUT VOLTAGE

vs. LOAD CURRENT

MAX1954A toc02

LOAD CURRENT (A)

OUTPUT VOLTAGE (V)

VIN = V

HSD

= 5V

-70

-30

-50

10

-10

50

30

70

3.0 4.03.5 4.5 5.0 5.5

OUTPUT VOLTAGE CHANGE

vs. INPUT VOLTAGE

MAX1954A toc03

INPUT VOLTAGE (V)

CHANGE IN OUTPUT VOLTAGE (mV)

V

OUT

= 2.5V

V

OUT

= 0.8V

VIN = V

HSD

I

OUT

= 5A

0.81

0.81

0.80

0.80

0.79

10.8 12.011.4 12.6 13.2

OUTPUT VOLTAGE

vs. INPUT VOLTAGE

MAX1954A toc04

INPUT VOLTAGE (V)

OUTPUT VOLTAGE (V)

VIN = V

HSD

I

OUT

= 5A

250

270

310

290

330

350

3.0 4.03.5 4.5 5.0 5.5

OSCILLATOR FREQUENCY

vs. INPUT VOLTAGE

MAX1954A toc05

INPUT VOLTAGE (V)

OSCILLATOR FREQUENCY (kHz)

TA = -40°C

TA = +85°C

TA = +25°C

VIN = V

HSD

LOAD TRANSIENT

MAX1954A toc06

40µs/div

100mV/div

V

OUT

AC-COUPLED

I

OUT

5A/µs

5A

500mA

MAX1954A

Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

LOAD TRANSIENT

MAX1954A toc07

40µs/div

100mV/div

V

OUT

AC-COUPLED

I

OUT

5A/µs

5A

2.5A

NO-LOAD SWITCHING WAVEFORMS

MAX1954A toc08

2µs/div

2A/div

I

L

DH

LX

DL

5V/div

10V/div

5V/div

HEAVY-LOAD SWITCHING WAVEFORMS

I

LOAD

= 5A

MAX1954A toc09

2µs/div

2A/div

I

L

DH

LX

DL

5V/div

10V/div

5V/div

SHORT CIRCUIT AND RECOVERY

MAX1954A toc11

200µs/div

1V/div

V

OUT

V

IN

I

LX

5A/div

2V/div

I

IN

2A/div

POWER-UP/POWER-DOWN WAVEFORMS

MAX1954A toc10

4ms/div

5V/div

V

IN

V

OUT

I

LX

5A/div

2V/div

STARTUP INTO PREBIASED OUTPUT

(OUTPUT PREBIASED AT ~1.7V)

MAX1954A toc12

2ms/div

1V/div

V

OUT

V

IN

DL

5V/div

5V/div

DH

5V/div