MAX1512 Datasheet, PDF (11/12 Pages) Maxim Integrated Products – EEPROM-Programmable TFT VCOM Calibrator

EEPROM-Programmable TFT VCOM Calibrator
Applications Information
The VCOM adjustment and the EEPROM programming
must be performed with an external programming cir-
cuit. Refer to the MAX1512 evaluation kit for a complete
programming circuit solution.
Use a circuit similar to the conceptual diagram shown
in Figure 8 to drive CTL. The accuracy of the program-
ming voltage (V_PP) is critical for proper MAX1512 data
retention. The use of a comparator is recommended to
verify the correct programming voltage has been
reached. A complete design example of a CTL pro-
gramming circuit is presented in the MAX1512 evalua-
tion kit data sheet.
Electrostatic Discharge (CTL)
The CTL pin is exposed at the LCD panel connector and
is subject to electrostatic discharge (ESD). Often an RC
filter is used to improve an input’s resilience to ESD. If a
filter is added between the LCD panel connector and
CTL, ensure that the RC time constant is short enough to
avoid interfering with CTL pulses or the EEPROM pro-
gramming timing. An RC time constant less than 200µs
does not interfere with EEPROM programming.
Leakage Current (CTL)
The CTL pin is internally biased to V_DD / 2, but it is sen-
sitive to leakage currents above 0.1µA. When CTL is
not driven, avoid leakage currents around the CTL pin.
Otherwise, reinforce the V_DD / 2 set point with an exter-
nal resistive voltage-divider.
Layout Information
Use the following guidelines for good layout:
• Place the VCOM buffer and the R1/R2 voltage-
divider close to the OUT pin (Figure 1). Keep the
VCOM buffer and the R1/R2 voltage-divider close
to each other.
• Place R_SET close to SET.
• In noisy environments, bypass capacitors may be
desired on V_DD and/or V_AVDD. Keep any bypass
capacitors close to the IC with short connections to
the pins.
Refer to the MAX1512 evaluation kit for an example of
proper board layout.
USER
INTERFACE
µC
DAC
0 TO 2.5V
REF
V_PP VERIFY
0 TO 15.5V
CTL
MAX1512
Figure 8. Conceptual Programming Circuit
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