Rainbow Electronics MAX686 - Manual

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
____________________________Features
♦ Internal 500mA, 28V N-Channel Switch
(no external FET required)
♦ Adjustable Output Voltage to +27.5V or -27.5V
♦ 6-Bit DAC-Controlled Output Voltage
♦ Up to 90% Efficiency
♦ Small 16-Pin QSOP Package
(Same size as 8-pin SO)
♦ Power-OK Indicator
♦ 65µA Quiescent Current
♦ 1.5µA Shutdown Current
♦ Up to 300kHz Switching Frequency
MAX686
DAC-Controlled Boost/Inverter
LCD Bias Supply with Internal Switch
________________________________________________________________ Maxim Integrated Products 1
19-1327; Rev 1; 2/98
PART
MAX686C/D
MAX686EEE -40°C to +85°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
Dice*
16 QSOP
EVALUATION KIT
AVAILABLE
Ordering Information
* Dice are specified at T A = +25°C, DC parameters only.
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 408-737-7600 ext. 3468.
Functional Diagram appears at end of data sheet.
MAX686
V CC
V DD
V OUT
22 µ H
V IN = 0.8V TO 27.5V
UP
SHDN
DN
POL
GND PGND
LX
DACOUT
LCDON
FB
REF
POK
ISET
0.1 µ F
R3
R2
MBR0530L
R1
ON/OFF
DAC CONTROL
V CC = 2.7V TO 5.5V
0.1 µ F
Typical Operating Circuit
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
PGND LX
N.C.
LCDON
GND
POK
FB
REF
TOP VIEW
MAX686
QSOP
UP
DN
ISET
POL
V DD V CC
SHDN
DACOUT
Pin Configuration