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 programming
voltage (V
PP
) is critical for proper MAX1512 data reten-
tion. The use of a comparator is recommended to verify
the correct programming voltage has been reached. A
complete design example of a CTL programming circuit
is presented in the MAX1512 evaluation kit data sheet.
Electrostatic Discharge (CTL, CE)
Often, CTL and CE are exposed at the panel connector
and are therefore subject to electrostatic discharge
(ESD). Resistor-capacitor (RC) filters can be employed
at these inputs to improve their ESD performance
(Figure 9).
If the CE panel connector is to be left floating after pro-
gramming, be sure to include a resistor to ground (R
CE
)
to ensure a valid logic-low on CE. The time constant for
a CE filter is not critical but the driving resistor must
have a much lower resistance than RCE to properly
drive CE.
If a filter is used at the CTL panel connector, its RC time-
constant should be short enough to avoid interfering with
CTL pulses or EEPROM programming timing. A time
constant less than 200µs does not interfere with EEP-
ROM programming. To avoid interfering with CTL puls-
es, make the time constant small compared to the CTL
pulsewidth used.
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.
MAX1512
EEPROM-Programmable TFT VCOM Calibrator
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