AT1367A/B/C/D
Preliminary Product Information
1MHz, 800mA Synchronous Buck Converter
With Power Good Detector & LDO
Typical Application Circuits ( Continued )
VIN
5.0V
10uF
AGND
4.7uH
SW
DELAY
10uF
27nF
To DSP
/PG
OUT1
To DSP
PG
OUT2
100K
100K
VOUT2
1.8V/400mA
2.2uF
From /PG
0.1uF 1M
VOUT1
3.3V/300mA
VBG
10nF
VCC
AT1367B
PGND
100K
Figure 5
Application Information
Capacitor Selection
In continuous mode, the source current of the top MOSFET is square wave of duty
cycle. The Primary function of the input capacitor is to provide a low impedance loop
for the edges of pulsed current drawn by the AT1367A/B/C/D. A load step at the
output can induce ringing at the input VIN. This ringing can couple to the output and
be mistaken as loop instability. The oscillation can be improved by add the
capacitance of the input capacitor. A typical value is 10µF ceramic (X5R or X7R),
POSCAP or Aluminum Polymer. These capacitors will provide good high frequency
bypassing and their low ESR will reduce resistive losses for higher efficiency. The
input capacitor RMS current varies with the input voltage and the output voltage. The
equation for the maximum RMS current in the input capacitor is:
V
O
V
(1
−
O
)
V
IN
V
IN
I
RMS
=
I
OMAX
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
3/2/2006 REV:1.2
Email:
service@aimtron.com.tw
8
AIMTRON [ AIMTRON TECHNOLOGY ]
