TPS65642A Datasheet, PDF (36/77 Pages) Texas Instruments – LCD Bias With Integrated Gamma Reference for Notebook PCs, Tablet PCs and Monitors

TPS65642A
SLVSC21 – OCTOBER 2013
www.ti.com
5.8 PANEL RESET / LCD BIAS READY (XAO)
The TPS65642A device provides an output signal through the XAO pin that is used to reset a level-shifter
or gate-driver IC during power up and power down. The GIP bit in the CONFIG register defines whether
the XAO pin works in GIP mode or non-GIP mode.
The primary purpose of the XAO signal in non-GIP applications is to drive the outputs of the display-panel
gate-driver IC high during power down by generating an active-low signal. When the GIP = 0, the XAO pin
is pulled low whenever V_IN < V_DET. The V_DET threshold voltage can be configured using the VDET register.
When the GIP = 1, the XAO output is used to delay the start of level-shifter activity during power up. The
delay time t_DLY6 starts when V_GH is done ramping up, and can be configured using the DLY6 register.
The XAO output is an open-drain type and requires an external pull up, typically in the range 10 kΩ to 100
kΩ.
5.9 PROGRAMMABLE V_COM CALIBRATOR
The programmable V_COM calibrator uses a digital-to-analog converter (DAC) to generate an offset current
I_DAC for an external resistor divider connected to AV_DD (see Figure 5-11 and Figure 5-12). Higher values of
the 7-bit digital word N written to the DAC generate higher I_DAC sink currents, and therefore lower V_COM
voltages.
Figure 5-11 shows the recommended circuit for the most commonly used application, when the LCD panel
requires only one V_COM supply voltage. The second op-amp is shown wired as a unity-gain buffer with an
input tied to GND (the recommended configuration if a second op-amp is not used), however, using a
second op-amp for other purposes, such as generating a half-AV_DD supply rail, is acceptable.
AV_DD
VCOM
DAC
I_SET
SMODE
V <V
IN
UVLO
I_DAC
&
R3
POS1
POS1
+
NEG1
–
R5
OUT1
V_COM1
V_FB1
V_REF
+
–
POS2
+
NEG2
–
OUT2
V_COM2
RSET
R_SET
Figure 5-11. Single-Programmable V_COM Supply
36
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