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General Description

The MAX1927/MAX1928 800mA step-down converters

power low-voltage microprocessors in compact equip-

ment requiring the highest possible efficiency. The

MAX1927/MAX1928 are optimized for generating low

output voltages (down to 750mV) at high efficiency

using small external components. The supply voltage

range is from 2.6V to 5.5V and the guaranteed minimum

output current is 800mA. 1MHz pulse-width modulation

(PWM) switching allows for small external components.

A unique control scheme minimizes ripple at light loads,

while maintaining a low 140µA quiescent current.

The MAX1927/MAX1928 include a low on-resistance

internal MOSFET switch and synchronous rectifier to

maximize efficiency and minimize external component

count. No external diode is needed. 100% duty-cycle

operation allows for a dropout voltage of only 340mV at

800mA. Other features include internal soft-start,

power-OK (POK) output, and selectable forced PWM

operation for lower noise at all load currents.

The MAX1928 is available with several preset output

voltages: 1.5V (MAX1928-15), 1.8V (MAX1928-18), and

2.5V (MAX1928-25). The MAX1927R has adjustable

output range down to 0.75V. The MAX1927/MAX1928

are available in a tiny 10-pin µMAX package.

Applications

WCDMA Handsets

PDAs and Palmtops

DSP Core Power

Battery-Powered Equipment

Features

♦ 800mA Output Current

♦ Output Voltages from 0.75V to 5V

♦ 2.6V to 5.5V Input Voltage Range

♦ Power-OK Output

♦ No Schottky Diode Required

♦ Selectable Forced PWM Operation

♦ 1MHz Fixed-Frequency PWM Operation

♦ 140µA Quiescent Current

♦ Soft-Start

♦ 10-Pin µMAX Package

MAX1927/MAX1928

Low-Output-Voltage, 800mA, PWM Step-Down

DC-DC Converters

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

BATT

COMP

GND

REF

PGND

POK

2.6V TO 5.5V

OUT

0.75V AT 800mA

SHDN

PWM

MAX1927R

Typical Operating Circuit

19-2527; Rev 0; 7/02

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.

PART

PRESET

OUTPUT

VOLTAGE

TEMP

RANGE

PIN-

PACKAGE

MAX1927REUB

Adj. to 0.75V -40°C to +85°C

10 µMAX

MAX1928EUB15

1.5V

-40°C to +85°C

10 µMAX

MAX1928EUB18

1.8V

-40°C to +85°C

10 µMAX

MAX1928EUB25

2.5V

-40°C to +85°C

10 µMAX

POK

BATT

PGNDFB

REF

GND

PWM

MAX1927R

MAX1928

µMAX

TOP VIEW

COMP SHDN

Pin Configuration

Summary of content (12 pages)

PAGE 1
9-2527; Rev 0; 7/02 Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters The MAX1927/MAX1928 800mA step-down converters power low-voltage microprocessors in compact equipment requiring the highest possible efficiency. The MAX1927/MAX1928 are optimized for generating low output voltages (down to 750mV) at high efficiency using small external components. The supply voltage range is from 2.6V to 5.5V and the guaranteed minimum output current is 800mA.
PAGE 2
MAX1927/MAX1928 Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters ABSOLUTE MAXIMUM RATINGS BATT, PWM, POK, COMP, SHDN to GND ...............-0.3V to +6V PGND to GND .......................................................-0.3V to +0.3V LX, REF, FB to GND ................................-0.3V to (VBATT + 0.3V) Continuous Power Dissipation (TA = +70°C) 10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........444mW Operating Temperature Range ...........................
PAGE 3
Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters (VBATT = 3.6V, SHDN = BATT, CREF = 0.1µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN N-Channel Synchronous Rectifier Turn-Off Threshold LX Leakage Current Maximum Duty Cycle -20 0.1 +20 15 0.85 15°C hysteresis µA % 0 PWM = BATT UNITS mA 100 PWM = GND Internal Oscillator Frequency Thermal Shutdown Threshold MAX 20 VBATT = 5.5V, LX = GND or BATT Minimum Duty Cycle TYP 1 1.
PAGE 4
MAX1927/MAX1928 Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters ELECTRICAL CHARACTERISTICS (continued) (VBATT = 3.6V, SHDN = BATT, CREF = 0.1µF, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER FB Input Current CONDITIONS P-Channel On-Resistance N-Channel On-Resistance MAX UNITS 150 nA 1.22 1.269 V 2 mV MAX1927R Reference Voltage Accuracy Reference-Supply Rejection PWM CONTROLLER MIN 2.6V < VBATT < 5.5V VBATT = 3.6V 0.4 VBATT = 2.6V 0.
PAGE 5
Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters MAX1928-25 EFFICIENCY vs. LOAD CURRENT VIN = 5V 60 50 VIN = 5V 70 60 10 100 40 40 30 VOUT = 1.8V 1 1000 10 100 1000 LOAD CURRENT (mA) MAX1928-15 EFFICIENCY vs. LOAD CURRENT MAX1927R EFFICIENCY vs. LOAD CURRENT MAX1928-25 DROPOUT VOLTAGE vs. LOAD CURRENT 100 VIN = 2.7V 90 80 EFFICIENCY (%) 80 VIN = 5V 70 VIN = 3.6V 70 VIN = 5V VIN = 3.6V 60 50 50 40 40 500 450 DROPOUT VOLTAGE (mV) MAX1927 toc04 90 VOUT = 1.
PAGE 6
Typical Operating Characteristics (continued) (Circuits of Figure 3 and 4, TA = +25°C, unless otherwise noted.) MAXIMUM LOAD CURRENT vs. INPUT VOLTAGE POK WAVEFORM STARTUP WAVEFORM MAX1927 toc12 MAX1927 toc11 MAX1927 toc10 1.4 VOUT = 1V MAXIMUM LOAD CURRENT (A) MAX1927/MAX1928 Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters 1.2 SHDN 1.0 0.8 VOUT = 1.8V 5V/div VOUT = 2.5V 5V/div SHDN POK 0.6 1V/div VOUT 2V/div 0.4 0.2 IIN 200mA/div VOUT 2V/div 0 2.6 3.1 3.6 4.1 4.
PAGE 7
Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters PIN NAME FUNCTION 1 PWM Forced-PWM Input. Drive to GND to use PWM at medium to heavy loads and pulse-skipping at light loads. Drive to BATT to force PWM operation at all loads. 2 GND Ground 3 REF Internal 1.25V Reference. Bypass to GND with a 0.1µF capacitor. 4 FB 5 COMP Compensation Input. See the Compensation, Stability, and Output Capacitor section for compensation component selection. 6 SHDN Shutdown Control Input.
PAGE 8
MAX1927/MAX1928 Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters Detailed Description The MAX1927/MAX1928 PWM step-down DC-DC converters accept inputs as low as 2.6V, while delivering 800mA to output voltages as low as 0.75V. These devices operate in one of two modes to optimize noise and quiescent current. Under heavy loads, MAX1927/ MAX1928 operate in pulse-width modulation (PWM) mode and switch at a fixed 1MHz frequency. Under light loads, they operate in PFM mode to reduce power consumption.
PAGE 9
Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters PART LX R1 MAX1927R PRESET OUTPUT VOLTAGE MAX1927R FB R2 50kΩ Figure 2. Setting the Adjustable Output Voltage Applications Information Output Voltage Selection The MAX1927/MAX1928 have preset output voltages. In addition, the MAX1927R has an adjustable output. To set the output voltage at the preset voltage, connect FB to the output. See Table 1 for a list of the preset voltages and their corresponding part numbers.
PAGE 10
MAX1927/MAX1928 Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters For the MAX1928: cel out the dominant pole created by the output load and the output capacitance:  V   1   1  OUT CC =  × (gm ) ×   ×    2πfC   IOUT(MAX)   RCS  1 1 = 2π × RL × COUT 2π × RC × CC Resistors R1 and R2 are external to the MAX1927 (see the Setting the Output Voltage section). IOUT(MAX) is the maximum output current, R CS = 0.48V/A, and g m = 250µS for the MAX1927.
PAGE 11
Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters R × COUT Cf = ESR RC or 22pF, whichever is greater. Standard Application Circuits Figures 3 and 4 are standard applications circuits for the MAX1927/MAX1928. Figure 3 illustrates the preset output voltages (MAX1928), while Figure 4 shows the adjustable configuration (MAX1927). Table 2 lists part numbers and suppliers for the components used in these circuits.
PAGE 12
Package Information (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.) e 10LUMAX.EPS MAX1927/MAX1928 Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters 4X S 10 INCHES 10 H ÿ 0.50±0.1 0.6±0.1 1 1 0.6±0.1 BOTTOM VIEW TOP VIEW D2 MILLIMETERS MAX DIM MIN 0.043 A 0.006 A1 0.002 A2 0.030 0.037 0.120 D1 0.116 0.118 0.114 D2 0.116 0.120 E1 E2 0.114 0.118 H 0.187 0.199 L 0.