MAX887 Datasheet, PDF (1/12 Pages) Maxim Integrated Products – 100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter

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