Rainbow Electronics MAX1791 User Manual

General Description

The MAX1762/MAX1791 PWM step-down controllers
provide high efficiency, excellent transient response,
and high DC output accuracy needed for stepping
down high-voltage batteries to generate low-voltage
CPU core, I/O, and chipset RAM supplies in notebook
computers and PDAs.

Maxim’s proprietary Quick-PWM™ pulse-width modula­tor is a free-running constant on-time type with input
feed-forward. Its high operating frequency (300kHz)
allows small external components to be utilized in PC
board area-critical applications such as subnotebook
computers and smart phones. PWM operation occurs
at heavy loads, and automatic switchover to pulse-skip­ping operation occurs at lighter loads. The external
high-side P-channel and low-side N-channel MOSFETs
require no bootstrap components. The MAX1762/
MAX1791 are simple, easy to compensate, and do not
have the noise sensitivity of conventional fixed-frequen­cy current-mode PWMs.

These devices achieve high efficiency at a reduced
cost by eliminating the current-sense resistor found in
traditional current-mode PWMs. Efficiency is further
enhanced by their ability to drive synchronous-rectifier
MOSFETs. The MAX1762/MAX1791 come in a 10-pin
µMAX package and offer two fixed voltages (Dual
Mode™) for each device, 1.8V/2.5V/adj (MAX1762) and

3.3V/5.0V/adj (MAX1791).

________________________Applications

Notebooks Handy-Terminals

Subnotebooks PDAs

Digital Cameras Smart Phones

1.8V/2.5V Logic
and I/O Supplies

Features

♦ High Operating Frequency (300kHz)

♦ No Current-Sense Resistor

♦ Accurate Current Limit

♦ ±1% Total DC Error over Line and During

Continuous Conduction

♦ Dual Mode Fixed Output

1.8V/2.5V/adj (MAX1762)

3.3V/5.0V/adj (MAX1791)

♦ 0.5V to 5.5V Output Adjust Range

♦ 5V to 20V Input Range

♦ Automatic Light-Load Pulse Skipping Operation

♦ Free-Running On-Demand PWM

♦ Foldback Mode™ UVLO

♦ PFET/NFET Synchronous Buck

♦ 4.65V at 25mA Linear Regulator Output

♦ 5µA Shutdown Supply Current

♦ 230µA Quiescent Supply Current

♦ 10-Pin µMAX Package

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down

Controllers for Notebooks

________________________________________________________________ Maxim Integrated Products 1

19-1923; Rev 0; 1/01

Ordering Information

Typical Operating Circuit

1

2

3

4

5

10

9

8

7

6

DH

CS

DLOUT

FB

REF

VL

MAX1762
MAX1791

µ

MAX

TOP VIEW

GNDSHDN

VP

Pin Configuration

For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

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

V

BATT

(5V TO 20V)

PART TEMP. RANGE PIN-PACKAGE

MAX1762EUB -40°C to +85°C 10 µMAX
MAX1791EUB -40°C to +85°C 10 µMAX

VL

MAX1762
MAX1791

REF

FB

OUT

SHDN

VP

DH

CS

DL

GND

V

OUT

1.8V/3.3V

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down
Controllers for Notebooks

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

VP, SHDN to GND ..................................................-0.3V to +22V

VP to VL ..................................................................-0.3V to +22V

OUT, VL to GND .......................................................-0.3V to +6V

DL, FB, REF to GND ....................................-0.3V to (VL + 0.3V)

DH to GND....................................................-0.3V to (VP + 0.3V)

CS to GND ....................................................-2.0V to (VP + 0.3V)

REF Short Circuit to GND ...........................................Continuous

Continuous Power Dissipation (T

A

= +70°C)

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

Operating Temperature .......................................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature.........................................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

ELECTRICAL CHARACTERISTICS

(VVP= 15V, VL enabled, CVL= 1µF, C

REF

= 0.1µF, TA= 0 to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

(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.

VP Input Voltage Range V

VL Input Voltage Range V

OUT Output Voltage
(MAX1762, 1.8V Fixed)

OUT Output Voltage
(MAX1762, 2.5V Fixed)

OUT Output Voltage
(MAX1791, 3.3V Fixed)

OUT Output Voltage
(MAX1791, 5V Fixed)

OUT Output Voltage (Adj Mode)

Output Voltage Adjust Range 0.5 5.5 V
OUT Input Resistance Adjustable-output mode 300 800 1700 kΩ

FB Input Bias Current VFB = 1.3V -0.1 0.1 µA

Soft-Start Ramp Time Zero to full I

On-Time (Note 2) t

Minimum Off-Time (Note 2) t

VL Quiescent Supply Current

VP Quiescent Supply Current

VL Shutdown Supply Current VVL = 5V, SHDN = GND 2 15 µA
VP Shutdown Supply Current S HD N = GN D , m easur ed at V P , V

VL Output Voltage I

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

VP

VL (overdriven) 4.75 5.25 V

VVP = 5V to 20V, VVL = 4.75V to 5.25V,
FB = GND, continuous conduction mode

VVP = 5V to 20V, VVL = 4.75V to 5.25V,
FB = VL, continuous conduction mode

VVP = 5V to 20V, VVL = 4.75V to 5.25V,
FB = GND, continuous conduction mode

VVP = 7V to 20V, VVL = 4.75V to 5.25V,
FB = VL, continuous conduction mode

V

= 5V to 20V, VVL = 4.75V to 5.25V,

VP

FB = OUT, continuous conduction mode

LIM

V

= 1.25V, VVP = 6V 666 740 814

OUT

V

= 5V, VVP = 6V 2550 2830 3110

OUT

FB = GND, V
regulation point

FB = GND, OUT forced
above the regulation point,
V

= 20V

VP

= 0 to 25mA, VVP = 5V to 20V 4.5 4.65 4.75 V

LOAD

= 5V, OUT forced above the

VL

VVL = float 227 410

V

= 5V 93 200

VL

= 0 or 5V 4 12 µA

V L

V

V

V

V

VL

OUT

OUT

OUT

OUT

ON

OFF

520V

1.773 1.8 1.827 V

2.463 2.5 2.538 V

3.250 3.3 3.350 V

4.925 5 5.075 V

1.231 1.250 1.269 V

1700 µs

300 400 500 ns

153 260 µA

ns

µA

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down

Controllers for Notebooks

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VVP= 15V, VL enabled, CVL= 1µF, C

REF

= 0.1µF, TA= 0 to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

(Note 1)

Reference Voltage V

Reference Load Regulation I
REF Sink Current REF in regulation 10 µA

REF Fault Lockout Voltage Falling edge 1.6 V

Output Undervoltage Threshold
(Foldback)

Output Undervoltage Lockout
Time (Foldback)

Current Limit Threshold V

Thermal Shutdown Threshold Hysteresis = 10oC 160

VL Undervoltage Lockout
Threshold

DH Gate Driver On-Resistance VVP = 6V to 20V, measure at 50mA 5 8 Ω

DL Gate Driver On-Resistance
(Pullup)

DL Gate Driver On-Resistance
(Pulldown)

DH Gate Driver Source/Sink
Current

DL Gate Driver Sink Current VDL = 2.5V 0.9 A

DL Gate Driver Source Current V

SHDN Logic Input High
Threshold Voltage

SHDN Logic Input Low
Threshold Voltage

Dual Mode Threshold Voltage

SHDN Logic Input Current SHDN = 0 or 5V -2 2 µA

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

= 4.75V to 5.25V, no load 1.98 2 2.02 V

VL

= 0 to 50µA 0.01 V

REF

With respect to regulation point, no load 60 70 80 %

ILIM

V

V

From SHDN signal going high V
regulation point

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

DL, high state, measure at 50mA 5 8 Ω

DL, low state, measure at 50mA 1 5 Ω

V

= 3V, VVP = 6V 0.6 A

DH

= 2.5V 0.5 A

DL

IH

IL

MAX1762 V

MAX1791 V

MAX1762 V

MAX1791 V

= 1.8V fixed

OUT

= 3.3V fixed

OUT

= 2.5V fixed

OUT

= 5V fixed

OUT

OUT

< 0.6 x

10 20 42 ms

-90 -100 -110 mV

4.1 4.4 V

1.6 V

0.6 V

50 100 150 mV

2.5 3.25 4 V

o

C

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down
Controllers for Notebooks

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS

(VVP= 15V, VL enabled, CVL= 1µF, C

REF

= 0.1µF, TA= -40 to +85°C, unless otherwise noted.) (Note 1)

VP Input Voltage Range V

VL Input Voltage Range V

OUT Output Voltage
(MAX1762, 1.8V Fixed)

OUT Output Voltage
(MAX1762, 2.5V Fixed)

OUT Output Voltage
(MAX1791, 3.3V Fixed)

OUT Output Voltage
(MAX1791, 5V Fixed)

OUT Output Voltage (adj Mode)

FB Input Bias Current VFB = 1.3V -0.2 0.2 µA

On-Time (Note 2) t

Minimum Off-Time (Note 2) t

VL Quiescent Supply Current

VP Quiescent Supply Current

VL Shutdown Supply Current VVL = 5V, SHDN = GND 15 µA
VP Shutdown Supply Current S HD N = GN D , m easur ed at V P , V

VL Output Voltage I

Reference Voltage VVL = 4.75V to 5.25V, no load 1.98 2.02 V

Reference Load Regulation I
REF Sink Current REF in regulation 10 µA

Output Undervoltage Threshold
(Foldback)

Output Undervoltage Lockout
Time (Foldback)

Current-Limit Threshold V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

VP

VL (overdriven) 4.75 5.25 V

VVP = 5V to 20V, VVL = 4.75V to 5.25V,
FB = GND, continuous conduction mode

VVP = 5V to 20V, VVL = 4.75V to 5.25V,
FB = VL, continuous conduction mode

VVP = 5V to 20V, VVL = 4.75V to 5.25V,
FB = GND, continuous conduction mode

VVP = 7V to 20V, VVL = 4.75V to 5.25V,
FB = VL, continuous conduction mode

V

= 5V to 20V, VVL = 4.75V to 5.25V,

VP

FB = OUT, continuous conduction mode

V

= 1.25V, VVP = 6V 666 814

OUT

= 5V, V

V

OUT

FB = GND, V
regulation point

FB = GND, OUT forced above
the regulation point V

= 0 to 25mA, VVP = 5V to 20V 4.5 4.75 V

LOAD

= 0 to 50µA 0.01 V

REF

With respect to regulation point, no load 60 80 %

From SHDN signal going high, V
regulation point

= 6V 2550 3110

VP

= 5V, OUT forced above the

VL

V

= float 410

V L

VP

= 20V

V

= 5V 200

V L

= 0 or 5V 12 µA

V L

< 0.6 x

OUT

V

V

V

V

VL

OUT

OUT

OUT

OUT

ON

OFF

ILIM

520V

1.773 1.827 V

2.463 2.538 V

3.250 3.350 V

4.925 5.075 V

1.231 1.269 V

250 550 ns

10 42 ms

-90 -110 mV

ns

260 µA

µA

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down

Controllers for Notebooks

_______________________________________________________________________________________ 5

Note 1: Specifications to -40°C are guaranteed by design, not production tested.
Note 2: One-shot times are measured at the DH pin (VP = 15V, C

DH

= 400pF, 90% point to 90% point; see drawing below for

measurement details).

ELECTRICAL CHARACTERISTICS (continued)

(VVP= 15V, VL enabled, CVL= 1µF, C

REF

= 0.1µF, TA= -40 to +85°C, unless otherwise noted.) (Note 1)

VL Undervoltage Lockout
Threshold

SHDN Logic Input High
Threshold Voltage

SHDN Logic Input Low
Threshold Voltage

Dual Mode Threshold Voltage

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

DH

90% 90%

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

V

IH

V

IL

MAX1762 V

MAX1791 V

MAX1762 V

MAX1791 V

t

ON

= 1.8V fixed

OUT

= 3.3V fixed

OUT

= 2.5V fixed

OUT

= 5V fixed

OUT

4.1 4.4 V

1.6 V

0.6 V

50 150 mV

2.5 4 V

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down
Controllers for Notebooks

6 _______________________________________________________________________________________

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

100

0

0.1 1 10 100 1000 10,000

MAX1762

EFFICIENCY vs. LOAD (2.5V)

20

MAX1762/91 toc01

LOAD CURRENT (mA)

EFFICIENCY (%)

40

60

80

10

30

50

70

90

VVP = 5V

VVP = 12V

VVP = 7V

VVP = 18V

100

0

0.1 1 10 100 1000 10,000

MAX1791

EFFICIENCY vs. LOAD (3.3V)

20

MAX1762/91 toc05

LOAD CURRENT (mA)

EFFICIENCY (%)

40

60

80

10

30

50

70

90

VVP = 18V

VVP = 12V

VVP = 7V

VVP = 5V

100

0

0.1 1 10 100 1000 10,000

MAX1791

EFFICIENCY vs. LOAD (3.0V)

20

MAX1762/91 toc06

LOAD CURRENT (mA)

EFFICIENCY (%)

40

60

80

10

30

50

70

90

VVP = 7V

VVP = 18V

VVP = 12V

VVP = 5V

-0.6

-0.4

-0.5

-0.2

-0.3

0

-0.1

0.1

0105 152025

VL VOLTAGE ERROR vs. OUTPUT CURRENT

MAX1762/91 toc08

VL CURRENT (mA)

VL VOLTAGE ERROR (%)

VVP = 12V

V

OUT

= 2.5V

100

0

0.1 1 10 100 1000 10,000

MAX1791

EFFICIENCY vs. LOAD (5V)

20

MAX1762/91 toc04

LOAD CURRENT (mA)

EFFICIENCY (%)

40

60

80

10

30

50

70

90

VVP = 7V

VVP = 18V

VVP = 12V

250

275

325

300

350

375

FREQUENCY vs. SUPPLY VOLTAGE

MAX1762/91 toc07

SUPPLY VOLTAGE (V)

FREQUENCY (kHz)

51181417

V

OUT

= 3.3V

V

OUT

= 5.0V

V

OUT

= 2.5V

V

OUT

= 1.8V

LOAD = 1A

100

0

0.1 1 10 100 1000 10,000

MAX1762

EFFICIENCY vs. LOAD (1.8V)

20

MAX1762/91 toc02

LOAD CURRENT (mA)

EFFICIENCY (%)

40

60

80

10

30

50

70

90

VVP = 18V

VVP = 12V

VVP = 5V

VVP = 7V

100

0

0.1 1 10 100 1000 10,000

MAX1762

EFFICIENCY vs. LOAD (1V)

20

MAX1762/91 toc03

LOAD CURRENT (mA)

EFFICIENCY (%)

40

60

80

10

30

50

70

90

VVP = 7V

VVP = 12V

VVP = 5V

VVP = 18V