19-0143; Rev 1; 2/95
NUAL
KIT MA
ATION
EET
EVALU
ATA SH
WS D
FOLLO
Digitally Adjustable LCD Bias Supply
________________________Applications
Notebook Computers
____________________________Features
o +2.0V to +6.0V Input Voltage Range
o Flexible Control of Output Voltage:
Digital Control
Potentiometer Adjustment
PWM Control
o Output Voltage Range Set by One Resistor
o Low, 60µA Max Quiescent Current
o 15µA Max Shutdown Mode
o Small Size – 8-Pin SO and Plastic DIP Packages
______________Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
Laptop Computers
MAX749CPA
0°C to +70°C
8 Plastic DIP
Palmtop Computers
MAX749CSA
0°C to +70°C
8 SO
Personal Digital Assistants
MAX749C/D
0°C to +70°C
Dice*
Communicating Computers
MAX749EPA
-40°C to +85°C
8 Plastic DIP
Portable Data-Collection Terminals
MAX749ESA
-40°C to +85°C
8 SO
* Contact factory for dice specifications.
__________Typical Operating Circuit
VIN +5V
__________________Pin Configuration
TOP VIEW
RSENSE
0.1µF
DIGITAL
ADJUST
ON/OFF
1
V+
CS
8
V+
3
4
CTRL
DLOW
FB
GND
RFB
6
5
-VOUT
1
8
CS
ADJ
2 ADJ
7
MAX749 DHI
2
7
DHI
6
DLOW
5
GND
CTRL 3
MAX749
FB 4
DIP/SO
CCOMP
_______________________________________________________________ Maxim Integrated Products
Call toll free 1-800-998-8800 for free samples or literature.
1
MAX749
_______________General Description
The MAX749 generates negative LCD-bias contrast
voltages from 2V to 6V inputs. Full-scale output voltage
can be scaled to -100V or greater, and is digitally
adjustable in 64 equal steps by an internal digital-toanalog converter (DAC). Only seven small surfacemount components are required to build a complete
supply. The output voltage can also be adjusted using
a PWM signal or a potentiometer.
A unique current-limited control scheme reduces supply
current and maximizes efficiency, while a high switching
frequency (up to 500kHz) minimizes the size of external
components. Quiescent current is only 60µA max and is
reduced to under 15µA in shutdown mode. While shut
down, the MAX749 retains the voltage set point, simplifying software control. The MAX749 drives either an
external P-channel MOSFET or a PNP transistor.
