Datasheet

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General Description

The MAX1556/MAX1556A/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/MAX1556A/MAX1557 contain a low-on-

resistance internal MOSFET switch and synchronous

rectifier to maximize efficiency and dropout perfor-

mance while minimizing external component count. A

proprietary topology offers the benefits of a high fixed-

frequency operation while still providing excellent effi-

ciency 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/MAX1556A/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

o Up to 97% Efficiency

o 95% Efficiency at 1mA Load Current

o Low 16µA Quiescent Current

o 1MHz PWM Switching

o Tiny 3.3µH Inductor

o Selectable 3.3V, 2.5V, 1.8V, 1.5V, 1.3V, 1.2V, 1.0V,

and Adjustable Output

o 1.2A Guaranteed Output Current

(MAX1556/MAX1556A)

o Voltage Positioning Optimizes Load-Transient

Response

o Low 27µA Quiescent Current in Dropout

o Low 0.1µA Shutdown Current

o No External Schottky Diode Required

o Analog Soft-Start with Zero Overshoot Current

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

MAX1556/MAX1556A/MAX1557

16µA I

, 1.2A PWM

Step-Down DC-DC Converters

________________________________________________________________

Maxim Integrated Products

TOP VIEW

OUT

SHDN

INP

GND

PGND

TDFN

MAX1556

MAX1556A

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

MAX1556A

MAX1557

Typical Operating Circuit

19-3336; Rev 3; 1/11

EVALUATION KIT

AVAILABLE

PART TEMP RANGE PIN-PACKAGE

TOP

MARK

MAX1556ETB+ -40°C to +85°C 10 TDFN-EP* ACQ

MAX1556ETB/V+T -40°C to +85°C 10 TDFN-EP* AWS

MAX1556AETB+ -40°C to +85°C 10 TDFN-EP* AUJ

MAX1557ETB+ -40°C to +85°C 10 TDFN-EP* ACR

EP = Exposed paddle.

Denotes a lead(Pb)-free/RoHS-compliant package.

/V denotes an automotive qualified part.

= Tape and reel.

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

Summary of content (12 pages)

PAGE 1
9-3336; Rev 3; 1/11 KIT ATION EVALU E L B A AVAIL 16µA IQ, 1.2A PWM Step-Down DC-DC Converters The MAX1556/MAX1556A/MAX1557 are low-operatingcurrent (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 pinselectable 1.8V, 2.5V, and 3.
PAGE 2
MAX1556/MAX1556A/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 (VIN = VINP = VSHDN = 3.6V, TA = -40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MAX1556, D1 = IN, D2 = GND; MAX1556A D1 = D2 = IN Line Regulation MAX1557, D1 = IN, D2 = GND MAX1556/MAX1556A p-Channel On-Resistance MAX1557 n-Channel On-Resistance p-Channel Current-Limit Threshold LX Leakage Current TYP VIN = 2.6V to 3.6V -0.37 VIN = 3.6V to 5.5V 0.33 VIN = 2.6V to 3.6V -0.1 VIN = 3.6V to 5.
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 (%) 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 0.1 10,000 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. INPUT VOLTAGE WITH 600mA LOAD 70 VIN = 3V VIN = 2.6V 1.81 1.80 1.
PAGE 5
16µA IQ, 1.2A PWM DC-DC Step-Down Converters EXTERNAL FEEDBACK SWITCHING WAVEFORMS LIGHT-LOAD SWITCHING WAVEFORMS SOFT-START/SHUTDOWN WAVEFORMS MAX1556/7 toc10b MAX1556/7 toc10 MAX1556/7 toc11 VOUT VLX VOUT 2V/div 0 200mA/div ILX 500mA/div 0 IIN 500mA/div 0 200mA/div ILX 0 0 ILX VIN = 5V, VOUT = 3.3V, IOUT = 500mA 2µs/div 4µs/div 100µs/div LOAD TRANSIENT SOFT-START RAMP TIME vs.
PAGE 6
MAX1556/MAX1556A/MAX1557 16µA IQ, 1.2A PWM DC-DC Step-Down Converters 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/MAX1556A/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 MAX1556A MAX1557 SS Figure 1. Functional Diagram L1 3.3µH INPUT 2.6V TO 5.5V INP R1 100Ω C4 0.47µF C1 10µF LX OUTPUT 0.
PAGE 8
Load-Transient Response/ Voltage Positioning The MAX1556/MAX1556A/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/MAX1556A/MAX1557 16µA IQ, 1.2A PWM DC-DC Step-Down Converters can be reduced by applying a correction factor to the feedback resistor equation. First, calculate the correction factor, k, by plugging the desired output voltage into the following formula: k = 1.06 x 10 −2 ⎛V − 0.75V ⎞ V x ⎜ OUTPUT ⎟ 3.6V ⎠ ⎝ OUTPUT R2 ERROR AMPLIFIER OUT R3 REFERENCE 1.25V k represents the shift in the operating point at the feedback node (OUT). Select the lower feedback resistor, R3, to be ≤ 35.
PAGE 11
16µA IQ, 1.2A PWM DC-DC Step-Down Converters PROCESS: BiCMOS Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
PAGE 12
MAX1556/MAX1556A/MAX1557 16µA IQ, 1.