MP1531 – LOW POWER, TRIPLE OUTPUT STEP-UP PLUS CHARGE PUMP FOR TFT BIAS
V
GH
OUTPUT
VOLTAGES
V
MAIN
V
IN
0V
V
GL
V
IN
IN
0V
V
EN-HIGH
EN
0V
POWER ON RESET
START 1
START 2
START 3
1.25V
CT
0V
V
IN
RDY
0V
TIME
Figure 2—Start-Up Timing Diagram
APPLICATION INFORMATION
Setting the Output Voltages
For the positive charge-pump, determine the
high-side resistor R9 by the equation:
Set the output voltage on each output by
selecting the resistive voltage divider ratio. The
voltage divider drops the output voltage to the
feedback threshold voltage. Use 10kꢀ to 50kꢀ
for the low-side resistor of the voltage divider.
VGH − VFB3
R9 =
V
⎛
⎞
FB3
⎜
⎜
⎟
⎟
R8
⎝
⎠
For the step-up converter, determine the
high-side resistor R1 by the equation:
For the negative charge-pump, determine the
high-side resistor R7 by the equation:
VMAIN − VFB1
R1 =
−VGL
R7 =
V
⎛
⎞
V
REF
⎛
⎞
FB1
⎜
⎜
⎟
⎟
⎜
⎜
⎟
⎟
R2
R5
⎝
⎠
⎝
⎠
Where VMAIN is the output voltage of the step-up
converter.
MP1531 Rev. 1.2
5/22/2006
www.MonolithicPower.com
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7
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