19-1142 Rev 0; 9/96
AN
N KIT M
LUATIO ABLE
EVA
AVAIL
UAL
100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter
____________________________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
_______________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.
MAX887
________________________Applications
Portable Instruments
Cellular Phones and Radios
Personal Communicators
Distributed Power Systems
Computer Peripherals
______________Ordering Information
PART
MAX887HC/D
MAX887HESA
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
Dice*
8 SO
*Contact
factory for availability. Dice are tested at T
A
= +25°C.
__________Typical Operating Circuit
V
IN
= 3.5V to 11V
V+
47µF
ON
0.33µF
LX
R1
165kΩ
47µF
33µH
V
OUT
= 3.3V
__________________Pin Configuration
TOP VIEW
SHDN
1
FB
2
REF
3
8
V+
LX
SYNC
GND
MAX887
SHDN
SYNC
VL
REF
C1
100pF
OFF
MAX887
7
6
5
FB
R2
100kΩ
VL
4
GND
2.2µF
0.047µF
V
OUT
= 1.25V (R1/R2 + 1)
SO
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
