Rainbow Electronics MAX1842 User Manual

MAX1742/MAX1842

1A/2.7A, 1MHz, Step-Down Regulators with

Synchronous Rectification and Internal Switches

________________________________________________________________ Maxim Integrated Products 1

19-1760; Rev 1; 2/02

General Description

The MAX1742/MAX1842 constant-off-time, pulse-width­modulated (PWM) step-down DC-DC converters are ideal
for use in 5V and 3.3V to low-voltage conversion neces­sary in notebook and subnotebook computers. These
devices feature internal synchronous rectification for high
efficiency and reduced component count. They require
no external Schottky diode. The internal 90mΩ PMOS
power switch and 70mΩ NMOS synchronous-rectifier
switch easily deliver continuous load currents up to 1A.
The MAX1742/MAX1842 produce a preset 2.5V, 1.8V, or

1.5V output voltage or an adjustable output from 1.1V to
VIN. They achieve efficiencies as high as 95%.

The MAX1742/MAX1842 use a unique current-mode,
constant-off-time, PWM control scheme, which includes
Idle Mode™ to maintain high efficiency during light-load
operation. The programmable constant-off-time architec­ture sets switching frequencies up to 1MHz, allowing the
user to optimize performance trade-offs between effi­ciency, output switching noise, component size, and
cost. Both devices are designed for continuous output
currents up to 1A. The MAX1742 uses a peak current
limit of 1.3A (min) and is suitable for applications requir­ing small external component size and high efficiency.
The MAX1842 has a higher current limit of 3.1A (min)
and is intended for applications requiring an occasional
burst of output current up to 2.7A. Both devices also fea­ture an adjustable soft-start to limit surge currents during
startup, a 100% duty cycle mode for low-dropout opera­tion, and a low-power shutdown mode that disconnects
the input from the output and reduces supply current
below 1µA. The MAX1742/MAX1842 are available in 16­pin QSOP packages.

For similar devices that provide continuous output cur­rents up to 2A and 3A, refer to the MAX1644 and
MAX1623 data sheets.

Applications

5V or 3.3V to Low-Voltage Conversion

CPU I/O Ring

Chipset Supplies

Notebook and Subnotebook Computers

Features

♦ ±1% Output Accuracy

♦ 95% Efficiency

♦ Internal PMOS and NMOS Switches

90mΩ On-Resistance at V

IN

= 4.5V

110mΩ On-Resistance at VIN= 3V

♦ Output Voltage

2.5V, 1.8V, or 1.5V Pin Selectable

1.1V to V

IN

Adjustable

♦ 3V to 5.5V Input Voltage Range

♦ 600µA (max) Operating Supply Current

♦ <1µA Shutdown Supply Current

♦ Programmable Constant-Off-Time Operation

♦ 1MHz (max) Switching Frequency

♦ Idle-Mode Operation at Light Loads

♦ Thermal Shutdown

♦ Adjustable Soft-Start Inrush Current Limiting

♦ 100% Duty Cycle During Low-Dropout Operation

♦ Output Short-Circuit Protection

♦ 16-Pin QSOP Package

PART

MAX1742EEE

-40°C to +85°C

TEMP RANGE PIN-PACKAGE

16 QSOP

Ordering Information

Idle Mode is a trademark of Maxim Integrated Products.

Typical Configuration

MAX1842EEE

-40°C to +85°C 16 QSOP

Pin Configuration appears at end of data sheet.

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.

EVALUATION KIT

AVAILABLE

INPUT

3V TO

5.5V

2.2µF

10Ω

470pF

IN

V

CC

SHDN
COMP
TOFF

MAX1742
MAX1842

LX

FB

PGND

GND

FBSEL

REF

SS

0.01µF

OUTPUT

1.1V TO
V

IN

1µF

MAX1742/MAX1842

1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= VCC= 3.3V, FBSEL = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

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.

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

IN to V

CC

.............................................................................±0.3V

GND to PGND.....................................................................±0.3V

All Other Pins to GND.................................-0.3V to (V

CC

+ 0.3V)

LX Current (Note 1).............................................................±4.7A

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

ESD Protection .....................................................................±2kV

Continuous Power Dissipation (T

A

= +70°C)
SSOP (derate 16.7mW/°C above +70°C;
part mounted on 1 in.

2

of 1oz. copper)...............................1W

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

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

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

Note 1: LX has internal clamp diodes to PGND and IN. Applications that forward-bias these diodes should take care not to exceed

the IC’s package power dissipation limits.

Input Voltage V

Preset Output Voltage V

Adjustable Output Voltage
Range

AC Load Regulation Error 2%

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

IN

, V

OUT

3.0 5.5 V

CC

TA = +25°C

FBSEL =
V

CC

VIN = 3V to

5.5V,
I

= 0

LOAD

to 1A for
MAX1742,

= 0

I

LOAD

to 2.5A for
MAX1842,
V

= V

FB

VIN = VCC = 3V to 5.5V, I
FBSEL = GND

FBSEL =
unconnected

FBSEL =
REF

OUT

FBSEL =
GND

LOAD

to +85°C

TA = +0°C
to +85°C

TA = +25°C
to +85°C

= +0°C

T

A

to +85°C

TA = +25°C
to +85°C

T

= +0°C

A

to +85°C

TA = +25°C
to +85°C

T

= +0°C

A

to +85°C

= 0,

DC Load Regulation Error 0.4 %
Dropout Voltage V

Reference Voltage V

Reference Load Regulation ∆V
PMOS Switch

On-Resistance

NMOS Switch

On-Resistance

R

R

DO

REF

ON, P ILX

ON, N ILX

V

= VCC = 3V, I

IN

TA = +25°C to +85°C 1.089 1.100 1.111

TA = +0°C to +85°C 1.084 1.100 1.117

REF IREF

= -1µA to +10µA 0.5 2 mV

= 0.5A

= 0.5A

= 1A 250 mV

LOAD

V

= 4.5V 90 200

IN

V

= 3V 110 250

IN

V

= 4.5V 70 150

IN

V

= 3V 80 200

IN

2.500 2.525 2.550

2.487 2.525 2.563

1.500 1.515 1.530

1.492 1.515 1.538

1.800 1.818 1.836

1.791 1.818 1.845

1.089 1.100 1.111

1.084 1.100 1.117

V

REF

V

IN

V

V

V

mΩ

MAX1742/MAX1842

1A/2.7A, 1MHz, Step-Down Regulators with

Synchronous Rectification and Internal Switches

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VIN= VCC= 3.3V, FBSEL = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

MAX1742 1.3 1.5 1.7

Current-Limit Threshold I

LIMIT

MAX1842 3.1 3.6 4.1

A

RMS LX Output Current 3.1 A

MAX1742 0.1 0.3 0.5

Idle Mode Current Threshold I

IM

MAX1842 0.3 0.6 0.9

A

Switching Frequency f (Note 2) 1

MHz

No-Load Supply Current

VFB = 1.2V

µA

Shutdown Supply Current

SHDN = GND <1 5 µA

PMOS Switch Off-Leakage

Current

I

IN

SHDN = GND 15 µA

Thermal Shutdown Threshold

Hysteresis = 15°C

°C

Undervoltage Lockout Threshold

V

IN

falling, hysteresis = 90mV 2.5 2.6 2.7 V

FB Input Bias Current I

FB

V

FB

= 1.2V 0 60

nA

R

TOFF

= 110kΩ 0.9

1.1

R

TOFF

= 30.1kΩ

Off-Time Default Period t

OFF

R

TOFF

= 499kΩ 3.8 4.5 5.2

µs

Off-Time Startup Period t

OFF

FB = GND 4

✕

t

OFF

µs

On-Time Period t

ON

(Note 2) 0.4 µs

SS Source Current I

SS

4 5 6 µA

SS Sink Current I

SS

V

SS

= 1V

µA

SHDN Input Current

V

SHDN

= 0 to V

CC

-1 1 µA

SHDN Input Low Threshold V

IL

0.8 V

SHDN Input High Threshold V

IH

2.0 V

FBSEL Input Current -4 +4 µA

FBSEL = GND 0.2

FBSEL = REF 0.9 1.3

FBSEL = unconnected

- 0.2

+0.2

FBSEL Logic Thresholds

FBSEL = V

CC

V

CC

V

IIN + I

I

CC

T
V

CC

(SHDN)

SHDN

UVLO

350 600

160

1.00

0.24 0.30 0.37

I

SHDN

100

0.7 ✕ VCC

- 0.2

0.7 ✕ VCC

250

MAX1742/MAX1842

1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS

(VIN= VCC= 3.3V, FBSEL = GND, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 3)

Note 2: Recommended operating frequency, not production tested.
Note 3: Specifications from 0°C to -40°C are guaranteed by design, not production tested.

PARAMETER

CONDITIONS

UNITS

Input Voltage V

IN

3.0 5.5 V

VIN = 3V to 5.5V,
FBSEL = V

CC

FBSEL = REF

Preset Output Voltage V

OUT

I

LOAD

= 0 to 1A
for MAX1742,
I

LOAD

= 0 to 2.5A
for MAX1842,
V

FB

= V

OUT

FBSEL = GND

V

Adjustable Output Voltage
Range

VIN = VCC = 3V to 5.5V, I

LOAD

= 0,

FBSEL = GND

V

IN

V

Reference Voltage V

REF

V

V

IN

= 4.5V

PMOS Switch

On-Resistance

I

LX

= 0.5A

V

IN

= 3V

V

IN

= 4.5V

NMOS Switch

On-Resistance

I

LX

= 0.5A

V

IN

= 3V

mΩ

MAX1742 1.2 1.8

Current-Limit Threshold I

LIMIT

MAX1842 2.9 4.3
MAX1742

Idle Mode Current Threshold I

IM

MAX1842 0.2 1.0

A

No-Load Supply Current

VFB = 1.2V

µA

FB Input Bias Current I

FB

VFB = 1.2V 0

nA

Off-Time Default Period t

OFF

R

TOFF

= 110kΩ

µs

SYMBOL

MIN MAX

2.475 2.575

FBSEL = unconnected 1.485 1.545

1.782 1.854

1.078 1.122

V

REF

1.078

R

ON, P

R

ON, N

0.05

IIN + I

CC

0.85 1.15

1.122
200
250
150
200

0.55

600

300

Typical Operating Characteristics

(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)

MAX1742/MAX1842

1A/2.7A, 1MHz, Step-Down Regulators with

Synchronous Rectification and Internal Switches

_______________________________________________________________________________________ 5

MAX1742

EFFICIENCY vs. OUTPUT CURRENT

= 5.0V, L = 6.0µH)

(V

100

95

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

0.001 0.01 1

V

V

= 1.8V, R

OUT

f = 833kHz

V

IN

= 2.5V, R

OUT

OUT

TOFF

= 75kΩ,

TOFF

= 1.5V, R

TOFF

OUTPUT CURRENT (A)

= 47kΩ, f = 926kHz

= 100kΩ, f = 692kHz

0.1

MAX1742 toc01

EFFICIENCY (%)

100

V

95

90

85

80

75

70

65

60

55

50

0.001 0.01 1

MAX1742

NORMALIZED OUTPUT ERROR

vs. OUTPUT CURRENT

0.5

0.4

0.3

VIN = 5V, V

0.2

0.1

0

-0.1

-0.2

-0.3

NORMALIZED OUTPUT ERROR (%)

-0.4

-0.5

0.001 0.01 1

= 1.5V, L = 6µH

OUT

VIN = 3.3V, V

OUTPUT CURRENT (A)

OUT

0.1

= 1.5V

MAX1742 toc04

EFFICIENCY vs. OUTPUT CURRENT

= 2.5V, R

OUT

V

OUT

MAX1742

= 3.3V, L = 3.9µH)

(V

IN

= 36kΩ, f = 456kHz

TOFF

V

= 1.8V, R

OUT

= 1.5V, R

TOFF

= 56kΩ, f = 833kHz

TOFF

OUTPUT CURRENT (A)

= 43kΩ, f = 869kHz

0.1

1100

1000

FREQUENCY (kHz)

EFFICIENCY vs.OUTPUT CURRENT

(f

PWM

VIN = 5V, V

µH, R

L = 15

OUTPUT CURRENT (A)

MAX1742 toc02

100

95

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

0.001 0.01 1

MAX1742

SWITCHING FREQUENCY

vs. OUTPUT CURRENT

VIN = 5V, V

900

800

700

600

500

400

300

200

100

0

0 0.2 0.4 0.6 0.8 1.0

= 2.5V, L = 6µH

OUT

VIN = 5V, V

OUT

VIN = 3.3V, V

OUTPUT CURRENT (A)

= 1.5V, L = 3.9µH

OUT

= 1.5V, L = 6µH

MAX1742

= 270kHz)

= 1.8V,

OUT

= 240kΩ

TOFF

VIN = 3.3V, V

µH, R

L = 10

OUT

TOFF

0.1

MAX1742 toc03

= 1.8V,
= 160kΩ

MAX1742 toc05