
LM8342
Programmable TFT V
COM
Calibrator with Non-Volatile
Memory
General Description
The LM8342 is an integrated combination of a non-volatile
register (7 bits EEPROM) and a DAC controlled current
source. Using the LM8342, the V
calibration procedure
is simplified by elimination of the potentiometer adjustment
task. This adjustment task is currently performed at the
factory using a trimmer adjustment tool and visual inspec-
tion.
The V
COM
adjustment can be done electronically in produc-
tion, using the I
2
C compatible interface. The factory operator
can physically view the screen head-on (frontal viewing)
when performing this step, easing manufacturing especially
for large TFT panels.
The V
level is typically at half AV
(determined by R1
and R2) and is buffered by the actual V
driver. By
controlling the level of I
, the V
level can be tuned.
The current level at the output of the LM8342 is a fraction
(1/128 to 128/128) of a maximum current which is set by
R
and an analog reference (AV
). The actual fraction is
determined by the 7-bit DAC. As a result, the output current
of the LM8342 has a good temperature stability yielding a
very stable V
adjustment. Controlling the DAC setting of
the LM8342 is done via its I
2
C compatible interface. The
actual DAC setting is stored in a volatile register. Using a
“Write to EE” command the data can be stored permanently
in the embedded EEPROM. At power on of the device, the
EEPROM data is copied to the volatile register, setting the
DAC. At any time, the data in the EEPROM can be changed
again via the I
2
C compatible interface.
Features
n
I
2
C compatible programmable DAC to set the output
current
n
Guaranteed monotonic DAC
n
Non-volatile memory to hold the setting
n
EEPROM in system programmable
n
No external programming voltage required
n
Maximum interface bus speed is 400 kHz
n
LLP-10 Package
Applications
n
TFT panel factory calibration
n
Digital potentiometer
n
Programmable current sink
Typical Application
20139201
November 2005
L
C
C
2005 National Semiconductor Corporation
DS201392
www.national.com