19-1406; Rev 1; 1/99
KIT
ATION
ET
EVALU
TA SHE
WS DA
FOLLO
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
General Description
The MAX1729 micropower step-up/step-down DC-DC
converter is ideally suited for electrically controlled bire-
fringence (ECB) and liquid-crystal-display (LCD) bias-
supply generation. It provides step-up/step-down
voltage conversion and reduces output ripple by using
a step-up DC-DC converter followed by a linear regula-
tor. This architecture permits a physically smaller induc-
tor than those used in competing SEPIC and flyback
topologies. This device features low quiescent current
(67µA typical). A logic-controlled shutdown mode fur-
ther reduces quiescent current to 0.4µA typical.
The MAX1729 features an input that dynamically
adjusts the output voltage to control display color or
contrast. It offers two feedback modes: internal and
external. Internal feedback mode allows output volt-
ages between 2.5V and 16V, and is specifically
designed to hold temperature drift to ±11ppm/°C.
External feedback mode allows the MAX1729 output
voltage range to be tailored for various displays.
An on-chip temperature sensor with a positive tempera-
ture coefficient provides compensation for LCD/ECB
display temperature characteristics. In internal feed-
back mode, the buffered temperature sensor output is
read and used to adjust the output voltage via a digital
control signal. External feedback mode features an
additional compensation method in which the tempera-
ture output is summed directly into the feedback net-
work to provide first-order negative temperature
compensation of the output voltage. The MAX1729 is
available in the space-saving 10-pin µMAX package.
o
±11ppm/°C Output Voltage Drift
o
On-Chip Temperature Sensor Output
o
Accurate Voltage and Temperature Provide:
Consistent ECB Colors
Consistent LCD Gray-Scale Contrast
o
+2.7V to +5.5V Input Voltage Range
o
Output Voltage Range
+2.5V to +16V in Internal Feedback Mode
Programmable in External Feedback Mode
o
Dynamic Control of the Output Voltage
o
67µA Supply Current
o
0.4µA Shutdown Current
o
10-Pin µMAX Package (1.09mm max height)
o
Evaluation Kit Available (MAX1729EVKIT)
Features
o
High-Accuracy Reference Voltage (±1%)
MAX1729
Ordering Information
PART
MAX1729EUB
TEMP. RANGE
-40°C to +85°C
PIN-PACKAGE
10 µMAX
Applications
ECB Display Bias & Color Adjustment
LCD Display Bias & Contrast Adjustment
Cellular Phones
Personal Digital Assistants
V
IN
2.7V to 5.5V
Typical Operating Circuit
IN
GND
LX
PS
Pin Configuration
TOP VIEW
IN
1
TC
REF
COMP
FB
2
3
4
5
10
GND
9
LX
PS
OUT
CTLIN
DIGITAL
PWM
CONTROLLER
ADC
REF
MAX1729
OUT
V
OUT
+2.5V to +16V
CTLIN
FB
MAX1729
8
7
6
TC
COMP
µMAX
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
