at1731a Aimtron Technology, at1731a Datasheet - Page 18

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

feedback input bias current and the potential for noise being coupled into the feedback pin. A
resistor network in the order of 200k Ω is recommended. The boost converter output voltage
is determined by the following relationship:
where V
Output Capacitor
The AT1731A is specially compensated to be stable with capacitors which have a worst- case
minimum value of 10uF at the particular V
also determine the minimum value and type of capacitors. Output ripple voltage consists of
two components the voltage drop caused by the switching current through the ESR of the
output capacitor and the charging and discharging of the output capacitor:
For low ESR ceramic capacitors, the output ripple is dominated by the charging or
discharging of the output capacitor.
Compensation
The Main step-up loop can be compensated by adjusting the external components connected
to the COMP pin. The COMP pin is connected to the output of the internal trans-conductance
error amplifier. The compensation capacitor adjusts the low frequency gain , and the series
resistor value adjusts the high frequency gain. The following formula calculates at what
frequency the resistor increases the high frequency gain.
If the device operates over the entire input voltage range from 2.7V to 5.5V, a larger
compensation capacitor up to 18pF is recommended. For a good load transient where no
oscillation should occur, 50 K Ω is recommended for R
Positive and Negative Charge Pump
The AT1731 contains two independent charge pump. The regulation of both the negative and
positive charge pumps is generated by the internal comparator that senses the output voltage
and compares it with and internal reference. The switching frequency of the charge pumps is
set to 0.5xf
on the load present.
V
V
f
MAIN
RIPPLE
Z
=
7F, No.9,PARK AVENUE. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: [phone]
2/8/2006 REV:1.1
2
=
×
=
V
REF
π
REF
I
LPEAK
×
OSC
=1.23V as specified.
1
C
×
. The pumps use pulse width modulation to adjust the pump period, depending
C

 

1
×
×
+
ESR
R
C
R
R
1
2
+

 

V
MAIN
V
Fax: [phone]
MAIN
−
V
in
×
C
OUT
I
MAIN
MAIN
×
f
OSC
18
being set. Output ripple voltage requirements
C
DC-DC Power IC for TFT Panel
Preliminary Product Information
resistor.
WWW:
Email:
http://www.aimtron.com.tw
[e-mail]
AT1731A