AT1731AP datasheet(13/22 Pages) AIMTRON

13 / 22 page

AT1731A

Preliminary Product Information

DC-DC Power IC for TFT Panel

7F, No.9,PARK AVENUE. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.

Tel: 886-3-563-0878

Fax: 886-3-563-0879

WWW: http://www.aimtron.com.tw

2/8/2006 REV:1.1

Email: service@aimtron.com.tw

forces the current through the inductor to ramp back down , transferring the energy stored in

the magnetic field to the output capacitor and load. To add higher flexibility to the selection

of external component values, the device uses external loop compensation.

Negative Charge-Pump Regulator

Negative charge-pump contains internal P-channel and N-channel MOSFETs to perform the

power transfer. The internal MOSFETs switch at a constant 600kHz (0.5x fOSC). The

charge-pump inverts the supply voltage (VDDN) and provides a regulated negative output

voltage. Figure 3 shows charge-pump block diagram. During the first half-cycle, the

P-channel MOSFET turns on and flying capacitor CCPN charges to VDDN minus a diode drop.

During the second half-cycle, the P-channel MOSFET turns off, and the N-channel MOSFET

turns on, level shifting CCPN. This connects CCPN in parallel with the reservoir capacitor CNEG.

If the voltage across CNEG minus a diode drop is lower than the voltage across CCPN, charge

flows from CCPN to CNEG until the diode turns off. The amount of charge transferred to the

output is controlled by the variable N-channel on-resistance.

Positive Charge-Pump Regulator

Positive charge-pump also contains internal P-channel and N-channel MOSFETs to perform

the power transfer. The internal MOSFETs switch at a constant 600kHz (0.5x fOSC). The

charge-pump inverts the doubles supply voltage (VDDP) and provides a regulated positive

output voltage. During the first half-cycle, the N-channel MOSFET turns on and flying

capacitor CCPP charges to VDDP minus a diode drop. During the second half-cycle, the

N-channel MOSFET turns off, and the P-channel MOSFET turns on, level shifting CCPP by

VDDP volts. This connects CCPP in series with the reservoir capacitor CPOS. If the voltage

across CPOS plus a diode drop is lower than the level shifted flying capacitor voltage

(VCPP+VDDP), charge flows from CCPP to CPOS until the diode turns off. The amount of charge

transferred to the output is controlled by the variable N-channel on-resistance.

CPP

Cout

FBN

SWN

R10

REF

1.23V

R11

NEG

CPN

Switch

Block

FBP

1.23V

SWP

DDN

Vmain

DDP

POS

CPOS

VDDP

Driver

VPOS =(1+R3/R4)x V

REF

VREF =1.23V

= -(R10/R11)x

NEG

=1.23V

REF

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