MAX686 Datasheet, PDF (1/16 Pages) Maxim Integrated Products – DAC-Controlled Boost/Inverter LCD Bias Supply with Internal Switch

19-1327; Rev 1; 2/98
EVAALVUAAILTAIOBNLEKIT
DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch
General Description
The MAX686 DAC-controlled boost/inverter IC converts
a positive input voltage to a positive or negative LCD
bias voltage up to +27.5V or -27.5V. The device features
an internal N-channel MOSFET switch, programmable
current limiting, and an internal 6-bit digital-to-
analog converter (DAC) for digital adjustment of the
output voltage. It comes in a small 16-pin QSOP pack-
age (same size as an 8-pin SO).
The MAX686 uses a current-limited, pulse-frequency-
modulation (PFM) control scheme to provide high effi-
ciency over a wide range of load conditions. Its high
switching frequency (up to 300kHz) allows the use of
small external components.
An LCDON output allows the LCD bias voltage to be
automatically disabled when the display logic voltage is
removed, protecting the display. The MAX686 has a
+2.7V to +5.5V input voltage range for the IC, and a
+0.8V to +27.5V input voltage range for the inductor.
Typical quiescent supply current is 65µA. Shutdown
current is 1.5µA.
The MAX686 offers high-level integration to save space,
reduce power consumption, and increase battery life,
making it an excellent choice for battery-powered
portable equipment. The MAX629 is similar to the
MAX686, except that it does not contain a built-in DAC.
Both devices have evaluation kits to facilitate designs.
Applications
Positive or Negative LCD Bias
Personal Digital Assistants
Notebook Computers
Portable Data-Collection Terminals
Palmtop Computers
Varactor Tuning Diode Bias
Pin Configuration
TOP VIEW
PGND 1
UP 2
DN 3
POL 4
V_DD 5
ISET 6
SHDN 7
DACOUT 8
MAX686
16 LX
15 N.C.
14 LCDON
13 GND
12 V_CC
11 POK
10 FB
9 REF
____________________________Features
o Internal 500mA, 28V N-Channel Switch
(no external FET required)
o Adjustable Output Voltage to +27.5V or -27.5V
o 6-Bit DAC-Controlled Output Voltage
o Up to 90% Efficiency
o Small 16-Pin QSOP Package
(Same size as 8-pin SO)
o Power-OK Indicator
o 65µA Quiescent Current
o 1.5µA Shutdown Current
o Up to 300kHz Switching Frequency
Ordering Information
PART
MAX686C/D
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
Dice*
MAX686EEE
-40°C to +85°C
16 QSOP
*Dice are specified at T_A = +25°C, DC parameters only.
Functional Diagram appears at end of data sheet.
Typical Operating Circuit
V_IN = 0.8V TO 27.5V
22µH
MBR0530L
V_OUT
V_CC = 2.7V TO 5.5V _VCC
0.1µF
V_DD
LX
DACOUT
LCDON
FB
DAC CONTROL
ON/OFF
UP ^MAX686
DN
POK
SHDN
REF
POL
GND
ISET
PGND
R2
R3
R1
0.1µF
QSOP
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