Rainbow Electronics MAX1557 User Manual

General Description

The MAX1556/MAX1557 are low-operating-current
(16µA), fixed-frequency step-down regulators. High effi­ciency, low-quiescent operating current, low dropout,
and minimal (27µA) quiescent current in dropout make
these converters ideal for powering portable devices
from 1-cell Li-ion or 3-cell alkaline/NiMH batteries. The
MAX1556 delivers up to 1.2A; has pin-selectable 1.8V,

2.5V, and 3.3V outputs; and is also adjustable. The
MAX1557 delivers up to 600mA; has pin-selectable 1V,

1.3V, and 1.5V outputs; and is also adjustable.

The MAX1556/MAX1557 contain a low-on-resistance
internal MOSFET switch and synchronous rectifier to
maximize efficiency and dropout performance while
minimizing external component count. A proprietary
topology offers the benefits of a high fixed-frequency
operation while still providing excellent efficiency at
both light and full loads. A 1MHz PWM switching fre­quency keeps components small. Both devices also
feature an adjustable soft-start to minimize battery tran­sient loading.

The MAX1556/MAX1557 are available in a tiny 10-pin
TDFN (3mm x 3mm) package.

Applications

PDAs and Palmtop Computers

Cell Phones and Smart Phones

Digital Cameras and Camcorders

Portable MP3 and DVD Players

Hand-Held Instruments

Features

♦ Up to 97% Efficiency

♦ 95% Efficiency at 1mA Load Current

♦ Low 16µA Quiescent Current

♦ 1MHz PWM Switching

♦ Tiny 3.3µH Inductor

♦ Selectable 3.3V, 2.5V, 1.8V, 1.5V, 1.3V, 1.0V, and

Adjustable Output

♦ 1.2A Guaranteed Output Current (MAX1556)

♦ Voltage Positioning Optimizes Load-Transient

Response

♦ Low 27µA Quiescent Current in Dropout

♦ Low 0.1µA Shutdown Current

♦ No External Schottky Diode Required

♦ Analog Soft-Start with Zero Overshoot Current

♦ Small, 10-Pin, 3mm x 3mm TDFN Package

MAX1556/MAX1557

16µA IQ, 1.2A PWM

Step-Down DC-DC Converters

________________________________________________________________ Maxim Integrated Products 1

TOP VIEW

LX

OUT

SHDN

6

7

8

9

10

INP

D1

3

2

1

SS

GND

IN

5

PGND

D2

4

TDFN

MAX1556/

MAX1557

Pin Configuration

Ordering Information

LX

SS

ON

OFF

SHDN

GND

INPUT

2.6V TO 5.5V

VOLTAGE

SELECT

OUTPUT

0.75V TO V

IN

PGND

OUT

INP

IN

D1

D2

MAX1556/

MAX1557

Typical Operating Circuit

19-3336; Rev 0; 7/04

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

PART

TEMP RANGE

PIN-PACKAGE

TOP

MARK

MAX1556ETB

10 TDFN-EP*
(T1033-1)

ACQ

MAX1557ETB

10 TDFN-EP*
(T1033-1)

ACR

*EP = Exposed paddle.

-40°C to +85°C

-40°C to +85°C

MAX1556/MAX1557

16µA IQ, 1.2A PWM DC-DC
Step-Down Converters

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= V

INP

= V

SHDN

= 3.6V, TA = - 40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) (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.

IN, INP, OUT, D2, SHDN to GND ..........................-0.3V to +6.0V

SS, D1 to GND.............................................-0.3V to (V

IN

+ 0.3V)

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

LX Current (Note 1)...........................................................±2.25A

Output Short-Circuit Duration.....................................Continuous

Continuous Power Dissipation (T

A

= +70°C)

10-Pin TDFN (derate 24.4mW/°C above +70°C) .......1951mW

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

PARAMETER CONDITIONS

UNITS

Input Voltage 2.6 5.5 V

Undervoltage-Lockout Threshold

VIN rising and falling, 35mV hysteresis (typ)

V

No switching, D1 = D2 = GND 16 25

Quiescent Supply Current

Dropout 27 42

µA

TA = +25°C 0.1 1

Shutdown Supply Current SHDN = GND

T

A

= +85°C 0.1

µA

Output Voltage Range

V

IN

V

No load

300mA load

0

600mA load

0

TA = 0°C to +85°C
(Note 2)

1200mA load, MAX1556 only

No load

300mA load

600mA load

Output Accuracy

T

A

= -40°C to +85°C

(Note 2)

1200mA load, MAX1556 only

%

MAX1556

Maximum Output Current

MAX1557

mA

TA = +25°C

0.1

D1 = D2 = GND

T

A

= +85°C

OUT Bias Current

For preset output voltages 3 4.5

µA

No load

300mA load

0

600mA load

D1 = D2 = GND,
V

OUT

= 0.75V at
300mA (typ),
T

A

= 0°C to +85°C

1200mA load, MAX1556 only

No load

300mA load

600mA load

FB Threshold Accuracy

D1 = D2 = GND,
V

OUT

= 0.75V
at 300mA (typ),
T

A

= -40°C to +85°C

1200mA load, MAX1556 only

%

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

the IC’s package power-dissipation limits.

MIN TYP MAX

2.20 2.35 2.55

0.75

-0.25 +0.75 +1.75

-0.75

-1.5 -0.75

-2.75 -2.25 -1.25

-0.75 +2.25

-1.5 +1.5

-2.25 +0.50

-4.0 -1.0

1200

600

0.01

0.01

-0.50 +0.75 +1.75

-1.2

-1.75 -0.75 +0.25

-3.25 -2.25 -1.25

-1.25 +2.25

-1.75 +1.50

-2.75 +0.25

-4.25 -1.00

+0.75

+1.2

MAX1556/MAX1557

16µA IQ, 1.2A PWM DC-DC

Step-Down Converters

_______________________________________________________________________________________ 3

Note 1: All units are 100% production tested at TA= +25°C. Limits over the operating range are guaranteed by design.
Note 2: For the MAX1556, 3.3V output accuracy is specified with a 4.2V input.

ELECTRICAL CHARACTERISTICS (continued)

(VIN= V

INP

= V

SHDN

= 3.6V, TA = - 40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) (Note 1)

PARAMETER CONDITIONS

MIN

TYP

MAX

UNITS

VIN = 2.6V to 3.6V

MAX1556,
D1 = IN, D2 = GND

V

IN

= 3.6V to 5.5V

VIN = 2.6V to 3.6V

Line Regulation

MAX1557,
D1 = IN, D2 = GND

V

IN

= 3.6V to 5.5V

%

VIN = 3.6V

MAX1556

V

IN

= 2.6V

VIN = 3.6V

0.7

p-Channel On-Resistance

MAX1557

V

IN

= 2.6V

Ω

VIN = 3.6V

n-Channel On-Resistance

V

IN

= 2.6V

Ω

MAX1556 1.5 1.8 2.1

p-Channel Current-Limit
Threshold

MAX1557 0.8 1.0 1.2

A

n-Channel Zero Crossing
Threshold

20 35 45 mA

MAX1556 1.8

RMS LX Output Current

MAX1557 1.0

TA = +25°C 0.1 10

LX Leakage Current

V

IN

= 5.5V, LX =

GND or IN

T

A

= +85°C 0.1

µA

Maximum Duty Cycle

%

Minimum Duty Cycle 0%

Internal Oscillator Frequency 0.9 1 1.1
SS Output Impedance ∆VSS / ISS for ISS = 2µA

300 kΩ

SS Discharge Resistance SHDN = GND, 1mA sink current 90 200 Ω

Thermal-Shutdown Threshold

°C

Thermal-Shutdown Hysteresis 15 °C

LOGIC INPUTS (D1, D2, SHDN)

Input-Voltage High 2.6V ≤ VIN ≤ 5.5V 1.4 V

Input-Voltage Low 0.4 V

TA = +25°C 0.1 1

Input Leakage

T

A

= +85°C 0.1

µA

-0.37

0.33

-0.1

0.09

0.19 0.35

0.23

0.35

0.42

0.27 0.48

0.33

100

130 200

+160

A

RMS

MHz

MAX1556/MAX1557

16µA IQ, 1.2A PWM DC-DC
Step-Down Converters

4 _______________________________________________________________________________________

Typical Operating Characteristics

(VIN= V

INP

= 3.6V, D1 = D2 = SHDN = IN, Circuits of Figures 2 and 3, TA= +25°C, unless otherwise noted.)

EFFICIENCY vs. LOAD CURRENT

WITH 3.3V OUTPUT

MAX1556/7 toc01

LOAD CURRENT (mA)

EFFICIENCY (%)

100101

60

70

80

90

100

50

40

0.1 1000 10,000

VIN = 5V

VIN = 3.6V

VIN = 4.2V

EFFICIENCY vs. LOAD CURRENT

WITH 2.5V OUTPUT

MAX1556/7 toc02

LOAD CURRENT (mA)

EFFICIENCY (%)

100101

60

70

80

90

100

50

40

0.1 1000 10,000

VIN = 3.6V

VIN = 3V

VIN = 2.6V

VIN = 5V

EFFICIENCY vs. LOAD CURRENT

WITH 1.8V OUTPUT

MAX1556/7 toc03

LOAD CURRENT (mA)

EFFICIENCY (%)

100101

60

70

80

90

100

50

40

0.1 1000 10,000

VIN = 5V

VIN = 3.6V

VIN = 3V

VIN = 2.6V

EFFICIENCY vs. LOAD CURRENT
WITH 1.0V OUTPUT (MAX1557)

MAX1556/7 toc04

LOAD CURRENT (mA)

EFFICIENCY (%)

100101

60

70

80

90

100

50

40

0.1 1000

VIN = 5V

VIN = 3.6V

VIN = 3V

VIN = 2.6V

OUTPUT VOLTAGE

vs. LOAD CURRENT

MAX1556/7 toc05

LOAD CURRENT (mA)

OUTPUT VOLTAGE (V)

1000800600400200

1.75

1.76

1.77

1.78

1.79

1.80

1.81

1.82

1.83

1.84

1.74
01200

TA = -45°C

TA = +25°C

TA = +85°C

OUTPUT VOLTAGE vs. INPUT VOLTAGE

WITH 600mA LOAD

MAX1556/7 toc06

INPUT VOLTAGE (V)

OUTPUT VOLTAGE (V)

5.04.54.03.53.0

1.780

1.781

1.782

1.783

1.784

1.785

1.786

1.787

1.788

1.789

1.779

2.5 5.5

TA = -40°C

TA = +25°C

TA = +85°C

OUTPUT VOLTAGE vs. INPUT VOLTAGE

WITH NO LOAD

MAX1556/7 toc07

INPUT VOLTAGE (V)

OUTPUT VOLTAGE (V)

5.04.54.03.53.0

1.804

1.805

1.806

1.807

1.808

1.809

1.810

1.811

1.812

1.803

2.5 5.5

TA = -40°C

TA = +25°C

TA = +85°C

SUPPLY CURRENT vs. INPUT VOLTAGE

MAX1556/7 toc08

INPUT VOLTAGE (V)

SUPPLY CURRENT (µA)

5432

2

4

6

8

10

12

14

16

18

20

0

16

HEAVY-LOAD SWITCHING WAVEFORMS

MAX1556/7 toc09

V

OUT

AC-COUPLED
10mV/div

V

LX

I

LX

2V/div
0

0

400ns

500mA/div

I

LOAD

= 750mA