at1731a Aimtron Technology, at1731a Datasheet - Page 17

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

Applications Information
External components of main boost converter can be designed by performing simple
calculations. It need to follow regulation by the output voltage and the maximum load current,
as well as maximum and minimum input voltages. Begin by selecting an inductor value.
Once L is know, choose the diode and capacitors.
Boost inductor
Inductor selection depends on input voltage, output voltage , maximum current , switching
frequency and availability of inductor values. The following boost circuit equations are
useful in choosing the inductor values based on the application. They allow the trading of
peak current and inductor value while allowing for consideration of component availability
and cost.
The peak inductor current is given by:
where:
△ I
D is the MOSFET turn on ratio and is decided by:
f
The inductor should be chosen to be able to handle this current and inductor saturation
current rating should be greater than I
Diode selection
The output diode has average current of I
peak current and a voltage rating at least 1.5 times the main output voltage. Schottky diode is
recommended and it should be able to handle those current.
Feedback Resistor Network
An external resistor divider is required to divide the output voltage down to the nominal
reference voltage. Current drawn by the resistor network should be limited to maintain the
overall converter efficiency . The maximum value of the resistor network is limited by the
∆
I
I
D
OSC
Lpeak
LAVG
I
=
L
L
7F, No.9,PARK AVENUE. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: [phone]
2/8/2006 REV:1.1
V
is the switching frequency.
=
is the inductor peak-to-peak current ripple and is decided by:
=
=
O
V
V
L
in
I
1
−
I
O
LAVG
V
MAIN
−
×
in
D
f
OSC
+
D
∆
2
I
L
Fax: [phone]
PEAK
.
MAIN
, and peak current the same as the inductor’s
17
DC-DC Power IC for TFT Panel
Preliminary Product Information
WWW:
Email:
http://www.aimtron.com.tw
[e-mail]
AT1731A