AT1367A Datasheet, PDF (9/14 Pages) Aimtron Technology – 1MHz, 800mA Synchronous Buck Converter With Power Good Detector & LDO

AT1367A/B/C/D
Preliminary Product Information
1MHz, 800mA Synchronous Buck Converter
With Power Good Detector & LDO
The output capacitor depends on the suitable ripple voltage. Low ripple voltage
corresponds to lower effective series resistance (ESR). The output ripple voltage is
determined by:
∆V_OUT
≅
∆I
L
(ESR
+
8
1
fC_OUT
)
The output capacitor RMS ripple current is given by:
I _RMS
=
1 V_OUT × (V_IN − V_OUT )
2 3 ^{L × f ×V}_IN
VBG Capacitor
A VBG pin is provided to decouple the bandgap reference voltage. An external
capacitor connected form VBG to GND reduces noise present on the internal
reference voltage, which in turn significantly reduces output noise and also improves
PSRR. Larger capacitor values may be used to further improve PSRR, but result in a
longer time period (slower turn on) to settle output voltage when power is initially
applied.
LDO
For general purposes, use a 2.2uF capacitor on the LDO output. Larger capacitor
values and lower ESR provide better supply noise rejection and transient response. A
higher value input capacitor may be necessary if large, fast transients are anticipated .
Ceramic capacitors have the lowest ESR, and will offer the best AC performance.
When choosing the input and output ceramic capacitors, choose the X5R or X7R
dielectric formulations. These dielectrics have the best temperature and voltage
characteristics of all the ceramics for a given value and size.
Inductor Selection
The inductor is chosen based on the desired ripple current. Large value inductors
lower ripple current and small value inductors result in higher ripple current. Always
consider the losses associated with the DCR and its effect on the total converter
7F, No.9, Park Avenue II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: [phone] Fax: [phone]
WWW: http://www.aimtron.com.tw
3/2/2006 REV:1.2
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