|TPS65167||Compact LCD Bias Supply for TFT-LCD TV Panels|
|TPS65167 Datasheet PDF : 42 Pages |
SLVS760C – APRIL 2007 – REVISED MARCH 2008
With CTRL=high, Q4 is turned on, and the charge pump output voltage is present at VGH. When the CTRL pin is
pulled low, then Q4 is turned off, and Q5 is turned on discharging VGH. The slope and time for discharging VGH
is determined by the LC Display capacitance and the termination on DRN. It is not required or recommended to
connect an additional output capacitor on VGH. There are three options available to terminate the DRN pin. The
chosen solution depends mainly on the LC Display capacitance and required overall converter efficiency.
1. td is set by the capacitor CE
2.The slope is set by the resistor RE
3. VL is set by the voltage applied to VD
Figure 28. High Voltage Switch (Gate Voltage Shaping) Timing Diagram
Option 1 in Figure 27 discharges VGH to Vs. The lower the resistor the faster the discharge.
Option 3 in Figure 27 constantly draws current from Vs due to the voltage divider connected to Vs. The
advantage of this solution is that the low level voltage VL is given by the voltage divider assuming the feedback
resistor values are small and allow to discharge the LC Display capacitance during the time, toff. Therefore, the
solution is not recommended for large display panels since the feedback divider resistors needs to be selected
too low which draws too much current from Vs.
Option 2 does not draw any current from Vs and; therefore, is better in terms of converter efficiency. The voltage
level VL where VGH is discharge to is determined by the LC Display capacitance, the resistor connected to DRN
and the off time, toff. The lower the resistor value connected to DRN the lower the discharge voltage level VL.
Adding any additional output capacitance to VGH is not recommend. If more capacitance is required, it needs to
be added to POUT instead.
High Voltage Stress Test (positive charge pump)
The TPS65167 incorporates a high voltage stress test where the output voltage of the boost converter Vs and
the positive charge pump POUT are set to a higher output voltage compared to the nominal programmed output
voltage. The High Voltage Stress test is enabled by pulling HVS pin to high. This sets POUT, respectively VGH
to 30 V, and the output voltage of the boost converter Vs is programmed to a higher voltage determined by the
resistor connected to RHVS. With HVS = high, the RHVS pin is pulled to GND which sets the voltage for the
boost converter during High Voltage Stress.
The TPS65167A has the high voltage stress test for the positive charge pump POUT disabled. The high voltage
stress test function is only enabled for the boost converter Vs.
Negative Charge Pump Driver
The negative charge pump provides a regulated output voltage set by the external resistor divider. The negative
charge pump inverts the input voltage applied to the SUPN pin and regulates it to the programmed voltage.
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