19-1142 Rev 0; 9/96
NUAL
KIT MA
UATION BLE
EVAL
AVAILA
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
________________________Applications
Portable Instruments
____________________________Features
o 95% Efficiency
o 600mA Output Current
o Cycle-by-Cycle Current Limiting
o Low-Dropout, 100% Duty-Cycle Operation,
300mV at 500mA
o Internal 0.6Ω (typ) MOSFET
o Internal Synchronous Rectifier
o High-Frequency Current-Mode PWM
o External SYNC or Internal 300kHz Oscillator
o Guaranteed 260kHz to 340kHz Internal Oscillator
Frequency Limits
o 2.5µA Shutdown Mode
______________Ordering Information
PART
Cellular Phones and Radios
MAX887HC/D
MAX887HESA
Personal Communicators
TEMP. RANGE
PIN-PACKAGE
0°C to +70°C
-40°C to +85°C
Dice*
8 SO
*Contact factory for availability. Dice are tested at TA = +25°C.
Distributed Power Systems
Computer Peripherals
__________Typical Operating Circuit
33µH
VIN = 3.5V to 11V
V+
0.33µF
47µF
OFF
2.2µF
ON
VOUT = 3.3V
LX
R1
165kΩ
MAX887
SHDN
SYNC
VL
REF
TOP VIEW
SHDN 1
R2
100kΩ
0.047µF
C1
100pF
8
V+
7
LX
REF 3
FB
GND
47µF
__________________Pin Configuration
6
SYNC
VL 4
5
GND
FB 2
MAX887
SO
VOUT = 1.25V (R1/R2 + 1)
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAX887
_______________General Description
The MAX887 high-efficiency, step-down DC-DC converter provides an adjustable output from 1.25V to
10.5V. It accepts inputs from 3.5V to 11V and delivers
600mA. Operation to 100% duty cycle minimizes
dropout voltage (300mV typ at 500mA). Synchronous
rectification reduces output rectifier losses, resulting in
efficiency as high as 95%.
Fixed-frequency pulse-width modulation (PWM)
reduces noise in sensitive communications applications. Using a high-frequency internal oscillator allows
tiny surface-mount components to reduce PC board
area, and eliminates audio-frequency interference. A
SYNC input allows synchronization to an external clock
to avoid interference with sensitive RF and dataacquisition circuits.
The MAX887 features current-mode operation for superior load/line-transient response. Cycle-by-cycle current
limiting protects the internal MOSFET and rectifier. A
low-current (2.5µA typ) shutdown mode conserves battery life.
