at1731a Aimtron Technology, at1731a Datasheet - Page 12

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

Function Description
The AT1731A is a multiple-output DC-DC converter IC which is designed primarily for use
in thin-film transistor (TFT) liquid crystal display (LCD) applications. It features a PWM
step-up converter operating with a fixed switching frequency of 1.2 MHz and uses internal
N-MOS to provide maximum efficiency . The output voltage of the main step-up converter
can be set from Vin to 15V with external resistive divider. A pair of charge-pump
independently regulate a positive output VDDP and a negative output VDDN for TFT
gate-on and gate-off supplies. AT1731A also consists of a precision 1.23V reference that
sources up to 50uA, logic shutdown , current-limited , soft-start, power-up sequencing ,
thermal shutdown and active low.
Main Boost converter
The boost converter operates in fast transient response , current-mode PWM and a constant
frequency of 1.2 MHz , allowing the use of smaller external inductor and output capacitors.
Depending on duty cycle of each switching cycle can regulate output voltage.
Figure 2 shows main step-up converter block diagram. On the rising edge of the internal
clock , the control and driver logic block sets internal flip-flop when the output voltage is too
low, which turns on the N-MOS . The external inductor current ramps up linearly , storing
energy in a magnetic filed. Once peak current of inductor over trans-conductance output
level , the N-MOS turns off, the flip-flop resets, and external schottky diode turns on . This
7F, No.9,PARK AVENUE. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: [phone]
2/8/2006 REV:1.1
SCP
lockout
Thermal
Protection
Undervoltage
Soft-Start
FB
Figure 2 Main Step-Up Converter block Diagram
Fax: [phone]
Slope
Compansation
OSC
Vin
Gm
12
COMP
Vin
Gm
DC-DC Power IC for TFT Panel
Preliminary Product Information
logic
Control
and Driver
Short Circuit
1.23V
Protection
Current
Limit
Current
sense
WWW:
Email:
NMOS
L
http://www.aimtron.com.tw
[e-mail]
FB
REF
GND
LX
PGND
R1
R2
C10
AT1731A
Vmain