Instruction Manual

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General Description

The MAX1556/MAX1557 are low-operating-current

(16µA), fixed-frequency step-down regulators. High effi-

ciency, 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 fre-

quency keeps components small. Both devices also

feature an adjustable soft-start to minimize battery tran-

sient 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 I

, 1.2A PWM

Step-Down DC-DC Converters

________________________________________________________________ Maxim Integrated Products 1

TOP VIEW

OUT

SHDN

INP

GND

PGND

TDFN

MAX1556/

MAX1557

Pin Configuration

Ordering Information

OFF

SHDN

GND

INPUT

2.6V TO 5.5V

VOLTAGE

SELECT

OUTPUT

0.75V TO V

PGND

OUT

INP

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

-40°C to +85°C

10 TDFN-EP*

(T1033-1)

ACQ

MAX1557ETB

-40°C to +85°C

10 TDFN-EP*

(T1033-1)

ACR

*EP = Exposed paddle.

Summary of content (12 pages)

PAGE 1
9-3336; Rev 0; 7/04 KIT ATION EVALU E L B AVAILA 16µA IQ, 1.2A PWM Step-Down DC-DC Converters 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.
PAGE 2
MAX1556/MAX1557 16µA IQ, 1.2A PWM DC-DC Step-Down Converters ABSOLUTE MAXIMUM RATINGS IN, INP, OUT, D2, SHDN to GND ..........................-0.3V to +6.0V SS, D1 to GND .............................................-0.3V to (VIN + 0.3V) PGND to GND .......................................................-0.3V to +0.3V LX Current (Note 1)...........................................................±2.25A Output Short-Circuit Duration.....................................
PAGE 3
16µA IQ, 1.2A PWM DC-DC Step-Down Converters MAX1556/MAX1557 ELECTRICAL CHARACTERISTICS (continued) (VIN = VINP = VSHDN = 3.6V, TA = - 40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER CONDITIONS MAX1556, D1 = IN, D2 = GND Line Regulation MAX1557, D1 = IN, D2 = GND MAX1556 p-Channel On-Resistance MAX1557 n-Channel On-Resistance p-Channel Current-Limit Threshold VIN = 3.6V to 5.5V 0.33 VIN = 2.6V to 3.6V -0.1 VIN = 3.6V to 5.5V 0.09 VIN = 3.6V 0.
PAGE 4
Typical Operating Characteristics (VIN = VINP = 3.6V, D1 = D2 = SHDN = IN, Circuits of Figures 2 and 3, TA = +25°C, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT WITH 2.5V OUTPUT EFFICIENCY (%) 70 60 80 70 40 VIN = 2.6V 60 1 10 100 1000 70 VIN = 5V VIN = 3.6V VIN = 3V 60 1 10 100 1000 10,000 0.1 1 10 10,000 LOAD CURRENT (mA) LOAD CURRENT (mA) EFFICIENCY vs. LOAD CURRENT WITH 1.0V OUTPUT (MAX1557) OUTPUT VOLTAGE vs. LOAD CURRENT OUTPUT VOLTAGE vs.
PAGE 5
16µA IQ, 1.2A PWM DC-DC Step-Down Converters (VIN = VINP = 3.6V, D1 = D2 = SHDN = IN, Circuits of Figures 2 and 3, TA = +25°C, unless otherwise noted.) SOFT-START/SHUTDOWN WAVEFORMS MAX1556/7 toc10 MAX1556/7 toc11 VOUT 1V/div 0 CSS = 470pF RLOAD = 4Ω 2V/div VLX 0 ILX 500mA/div 0 IIN 500mA/div 0 200mA/div 0 ILX SOFT-START RAMP TIME (ms) 5V/div 0 VSHDN 20mV/div AC-COUPLED VOUT SOFT-START RAMP TIME vs. CSS 10 MAX1556/7 toc12 LIGHT-LOAD SWITCHING WAVEFORMS 1 0.
PAGE 6
16µA IQ, 1.2A PWM DC-DC Step-Down Converters MAX1556/MAX1557 Pin Description PIN NAME 1 IN 2 GND FUNCTION Supply Voltage Input. Connect to a 2.6V to 5.5V source. Ground. Connect to PGND. Soft-Start Control. Connect a 1000pF capacitor (CSS) from SS to GND to eliminate input-current overshoot during startup. CSS is required for normal operation of the MAX1556/MAX1557. For greater than 22µF total output capacitance, increase CSS to COUT / 22,000 for soft-start.
PAGE 7
16µA IQ, 1.2A PWM DC-DC Step-Down Converters BIAS CURRENT-LIMIT COMPARATOR VCS CURRENT SENSE MAX1556/MAX1557 IN SHDN SHORT-CIRCUIT PROTECTION CLOCK 1MHz 0.675V PWM COMPARATOR INP PWM AUTO SKIP CONTROL LX SLOPE COMP PGND SKIP-OVER ENTER SKIP/ SR OFF ZERO-CROSS DETECT ERROR AMPLIFIER OUT REFERENCE 1.25V GND D1 OUTPUT VOLTAGE SELECTOR D2 MAX1556 MAX1557 SS Figure 1. Functional Diagram L1 3.3µH INPUT 2.6V TO 5.
PAGE 8
Load-Transient Response/ Voltage Positioning The MAX1556/MAX1557 match the load regulation to the voltage droop seen during transients. This is sometimes called voltage positioning. The load line used to achieve this behavior is shown in Figures 4 and 5. There is minimal overshoot when the load is removed and minimal voltage drop during a transition from light load to full load.
PAGE 9
16µA IQ, 1.2A PWM DC-DC Step-Down Converters MANUFACTURER PART VALUE (µH) DCR (mΩ) ISAT (mA) SIZE (mm) SHIELDED Taiyo Yuden LMNP04SB3R3N 3.3 36 1300 5 x 5 x 2.0 Yes Taiyo Yuden LMNP04SB4R7N 4.7 50 1200 5 x 5 x 2.0 Yes TOKO D52LC 3.5 73 1340 5 x 5 x 2.0 Yes TOKO D52LC 4.7 87 1140 5 x 5 x 2.0 Yes Sumida CDRH3D16 4.7 50 1200 3.8 x 3.8 x 1.8 Yes TOKO D412F 4.7 100* 1200* 4.8 x 4.8 x 1.2 Yes Murata LQH32CN 4.7 97 790 2.5 x 3.2 x 2.0 No Sumitomo CXL180 4.
PAGE 10
MAX1556/MAX1557 16µA IQ, 1.2A PWM DC-DC Step-Down Converters Inductor Selection A 4.7µH inductor with a saturation current of at least 800mA is recommended for the MAX1557 full-load (600mA) application. For the MAX1556 application with 1.2A full load, use a 3.3µH inductor with at least 1.34A saturation current. For lower full-load currents the inductor current rating can be reduced. For maximum efficiency, the inductor’s resistance (DCR) should be as low as possible.
PAGE 11
16µA IQ, 1.2A PWM DC-DC Step-Down Converters 6, 8, &10L, DFN THIN.EPS D N PIN 1 INDEX AREA E E2 DETAIL A CL CL L A L e e PACKAGE OUTLINE, 6, 8, 10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY 21-0137 F 1 2 ______________________________________________________________________________________ 11 MAX1556/MAX1557 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications.
PAGE 12
MAX1556/MAX1557 16µA IQ, 1.2A PWM DC-DC Step-Down Converters Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages. COMMON DIMENSIONS SYMBOL A MIN. MAX. 0.70 0.80 D 2.90 3.10 E 2.90 3.10 A1 L 0.00 0.05 k 0.40 0.20 0.25 MIN. A2 0.20 REF. PACKAGE VARIATIONS PKG. CODE N D2 E2 e JEDEC SPEC b [(N/2)-1] x e T633-1 6 1.50±0.10 2.30±0.10 0.