19-2527; Rev 0; 7/02
Low-Output-Voltage, 800mA, PWM Step-Down
DC-DC Converters
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 140碌A 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 碌MAX package.
o
800mA Output Current
o
Output Voltages from 0.75V to 5V
o
2.6V to 5.5V Input Voltage Range
o
Power-OK Output
o
No Schottky Diode Required
o
Selectable Forced PWM Operation
o
1MHz Fixed-Frequency PWM Operation
o
140碌A Quiescent Current
o
Soft-Start
o
10-Pin 碌MAX Package
Features
MAX1927/MAX1928
Ordering Information
PART
MAX1927REUB
PRESET
TEMP
PIN-
OUTPUT
PACKAGE
RANGE
VOLTAGE
Adj. to 0.75V -40掳C to +85掳C 10 碌MAX
1.5V
1.8V
2.5V
-40掳C to +85掳C 10 碌MAX
-40掳C to +85掳C 10 碌MAX
-40掳C to +85掳C 10 碌MAX
Applications
WCDMA Handsets
PDAs and Palmtops
DSP Core Power
Battery-Powered Equipment
MAX1928EUB15
MAX1928EUB18
MAX1928EUB25
Pin Configuration
TOP VIEW
PWM
1
GND
REF
FB
COMP
2
3
4
5
10
POK
9
BATT
V
IN
2.6V TO 5.5V
Typical Operating Circuit
PWM
L1
LX
SHDN
R
C
COMP
C
C
C
f
FB
C2
V
OUT
0.75V AT 800mA
BATT
C1
MAX1927R
MAX1928
8
LX
7
PGND
6
SHDN
MAX1927R
POK
碌MAX
REF
PGND
GND
________________________________________________________________
Maxim Integrated Products
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For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim鈥檚 website at www.maxim-ic.com.
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