19-0205; Rev 0; 7/94
T
N KI
ATIO
ALU LABLE
EV
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AVA
PDA/Hand-Held Computer Power Controller
____________________________Features
o +3.3V Step-Down Controller
o Dual PCMCIA 2.0 Compatible VPP Outputs
(0V/3.3V/5V/12V)
o Digitally Adjustable Switching Current Source for
Battery Charging
o 5 High-Side Switch Gate-Driver Outputs
o SPI Serial Interface
o 300kHz Switching Frequency
o Oscillator SYNC Input
o 2.5V ±1.5% Reference Output
o 36-Pin SSOP Package
________________________Applications
Subnotebook Computers
PDAs
Communicating Computers
Handy-Terminals
______________Ordering Information
PART
MAX781CBX
MAX781EBX
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
36 SSOP
36 SSOP
________________________________________________Typical Application Diagram
DCIN
(up to 18V)
SUBSYSTEMS
HIGH-SIDE GATE DRIVERS
5
LOAD
SWITCHES
MAX781
DIGITALLY
ADJUSTABLE
SWITCHING
CURRENT
SOURCE
5 to 8
NiCd/NiMH
CELLS
or
2 LION
CELLS
+3.3V AT 1A OR MORE
SERIAL INTERFACE
4
INTERRUPT
SELF REFRESH
DRAM
CPU
VPPA
PCMCIA
SLOT A
VPPB
PCMCIA
SLOT B
ANALOG MULTIPLEXER OUTPUT
ADC
Pin Configuration on last page.
™SPI is a trademark of Motorola Inc. Microwire is a trademark of National Semiconductor Corp.
Idle Mode is a trademark of Maxim Integrated Porducts.
________________________________________________________________ Maxim Integrated Products
Call toll free 1-800-998-8800 for free samples or literature.
1
MAX781
_______________General Description
The MAX781 is a system-engineered power-supply controller for subnotebook computers, PDAs, or similar battery-powered equipment. It provides high-performance,
step-down (buck), pulse-width modulated (PWM) control
for generating +3.3V and constant-current battery charging. Dual PCMCIA VPP outputs are powered by a regulated flyback winding. Five high-side gate drivers and a
buffered analog multiplexer are also included. All functions are controlled by an SPI/Microwire™ compatible
four-wire serial interface.
The MAX781 generates +3.3V with high efficiency through
synchronous rectification and PWM operation at heavy
loads. It uses Idle Mode™ operation at light loads. Only
small external components are required because of the
device’s high switching frequency (300kHz) and advanced
current-mode PWM architecture that allows for output
capacitance as low as 50µF per ampere of load.
The MAX781 is configured by 32 bits of serial data. These
bits select the operating mode, set the switch-mode battery charger current level, select one of eight analog multiplexer channels, and turn on/off the five high-side gate
drivers. A status byte read from the serial interface indicates if the battery has been removed, if the DC charging
source has been connected, or if there is a fault condition
on the +3.3V output. An interrupt output signals the CPU if
a status signal changes.
