Rainbow Electronics MAX887 - Manual

_______________General Description
The MAX887 high-efficiency, step-down DC-DC con-
verter 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 applica-
tions. 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 data-
acquisition circuits.
The MAX887 features current-mode operation for supe-
rior load/line-transient response. Cycle-by-cycle current
limiting protects the internal MOSFET and rectifier. A
low-current (2.5µA typ) shutdown mode conserves bat-
tery life.
________________________Applications
Portable Instruments
Cellular Phones and Radios
Personal Communicators
Distributed Power Systems
Computer Peripherals
____________________________Features
♦ 95% Efficiency
♦ 600mA Output Current
♦ Cycle-by-Cycle Current Limiting
♦ Low-Dropout, 100% Duty-Cycle Operation,
300mV at 500mA
♦ Internal 0.6
Ω
(typ) MOSFET
♦ Internal Synchronous Rectifier
♦ High-Frequency Current-Mode PWM
♦ External SYNC or Internal 300kHz Oscillator
♦ Guaranteed 260kHz to 340kHz Internal Oscillator
Frequency Limits
♦ 2.5µA Shutdown Mode
MAX887
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
________________________________________________________________ Maxim Integrated Products 1
1
2
8
7
V+
LX
SYNC
GND
SHDN
FB
REF
VL
MAX887
SO
TOP VIEW
3
4
6
5
__________________Pin Configuration
MAX887
REF
R1
165k Ω
R2
100k Ω
0.047 µ F
2.2 µ F
47 µ F 47 µ F
C1
100pF
0.33 µ F
33 µ H
V+ LX
FB
GND
SYNC
VL
SHDN
V OUT = 3.3V
V
OUT
= 1.25V (R1/R2 + 1)
V IN = 3.5V to 11V
ON
OFF
__________Typical Operating Circuit
19-1142 Rev 0; 9/96
PART
MAX887HC/D
MAX887HESA -40°C to +85°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
Dice*
8 SO
EVALUATION KIT MANUAL
AVAILABLE
______________Ordering Information
* Contact factory for availability. Dice are tested at T A = +25°C.
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800