ADD8754-EVAL AD [Analog Devices], ADD8754-EVAL Datasheet - Page 6

• Manufacturer Part Number: ADD8754-EVAL
• Description: Evaluation Kit for LCD Power, VCOM, and Gate Modulation
• Manufacturer: AD [Analog Devices]

ADD8754-EVAL
Setting VDD_1
The VDD_1 voltage is the GPM low ramp voltage. With R25
shorted and RZ open, the step-up output (BOOST_OUT) is
connected to VDD_1. This ramps the GPM_H waveform down
to the BOOST_OUT voltage level. If other voltages are desired,
a voltage divider or Zener diode can be used to set this voltage.
If a voltage divider is used, a low divider impedance (<1 kΩ) is
recommended. See the
information.
Adjusting the Delay and Ramp Rate
Capacitor CE adjusts the negative ramp delay of the VGH_M
waveform. RE adjusts the negative ramp rate of the VGH_M
waveform. See the ADD8754 data sheet for details.
VFLK Input
The amplitude of the input signal on VFLK must be between
2.5 V to 5.0 V. Typically, VFLK is a digital waveform that switches
from high to low for each horizontal line of the TFT-LCD
display (from TCON).
If a signal generator is used, the following settings are
recommended to simulate a 1280 × 1024 60 Hz panel:
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•
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AD5259 DIGITAL POTENTIOMETER (OPTIONAL)
If the ADD8754-EVAL includes an optional
potentiometer, the VCOM output voltage is set by using
Resistor R3, Resistor R4 and the programmed output resis-
tance of the 10 kΩ digital potentiometer, AD5259. Set the
components as shown in Table 3.
Digital pulse signal
3.3 V amplitude (low = 0 V, high = 3.3 V)
16 μs period
30% duty cycle
ADD8754
data sheet for more
AD5259
digital
Rev. A | Page 6 of 12
Table 3. AD5259 Component Differences
Label
C13
C23
R12
R13
R21
R22, R23
R24
R_SCA,
R_SCL
To use the programmable potentiometer
1.
2.
3.
4.
5.
Note that because the AD5259 is a low voltage part (supply from
LDO_OUT), the appropriate VCOM gain resistors must be
configured to raise the VCOM output voltage. If Resistor R13
and Resistor R21 are set to the values listed in Table 3, the gain
is set to +3.
For more information, see the AD5259 Evaluation Board User
Manual on the ADD8754 Evaluation Kit CD.
Connect the ADD8754-EVAL to the parallel port of a PC
using a parallel port cable.
Insert the CD from the evaluation kit into the CD drive
and click setup.exe to install the software.
Once installation is complete, open the AD5259 Evaluation
Board Program from the Start menu.
Enter data in the Enter Data text box and then click
Write to RDAC to write the data.
Click the Store RDAC Content to EEMEM button to store
the current RDAC setting to EEMEM.
Description
VCOM feedback capacitor
AD5259 VDD bypass capacitor
Variable resistor for VCOM positive input
VCOM feedback resistor
VCOM negative input resistor
AD5259 digital control pull-up resistor
VCOM positive input divider resistor (top)
AD5259 digital control series resistors
Value
Open
Open
10 kΩ
Open
Open
Open
15 kΩ
Open