at1731a Aimtron Technology, at1731a Datasheet - Page 14

• Manufacturer Part Number: at1731a
• Description: Dc-dc Power Ic For Tft Panel
• Manufacturer: Aimtron Technology

Shutdown
The AT1731A shuts down to reduce the supply current to 1uA when SHDN is low. In this
mode, the internal reference , error amplifier , comparators, and biasing circuitry turn off
while the N-channel MOSFET is turned off. The boost converter’s output is connected to Vin
normally. Do not leave SHDN pin floating. A logic-level transition on SHDN clears the fault
latch.
Power-Up Sequencing
The AT1731A goes through start-up sequence after power-up or exiting shutdown. First, the
reference power-up, then the main DC-DC step-up converter powers up with soft-start enable.
Once the main DC-DC step-up converter reaches regulation , the negative charge pump turns
on. When the negative charge pump output voltage reaches approximately 90% of its
nominal value (V
positive output voltage reaches 100% of its nominal value (V
sequence is completed, see figure 4.
Soft-Start
Soft-start allows a gradual increase of the internal current-limit level for the main step-up
converter during power-up to reduce input surge currents. As the internal 2uA current source
charges the external soft-start capacitor, the peak N-MOS current is limited by the voltage on
the capacitor. For the dual charge pumps , soft-start is achieved by in-turn controlling the
0V
0V
0V
0V
7F, No.9,PARK AVENUE. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
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2/8/2006 REV:1.1
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Nominal Regulator Value
<110mV) , then the positive charge pump starts up. Finally, when the
Nominal Regulator 100%
Nominal
Vmain
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Regulator 90%
Figure 3 Charge-Pump Block Diagram
Figure 4 Power Sequence
14
DC-DC Power IC for TFT Panel
Preliminary Product Information
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Vin
Shotdown signal
Step-up Vout
Positive Charge-Pump Vout
Negative charge-Pump Vout
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FBP
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>1.1V) .The power-up
AT1731A