Datasheet
I
RMS
+ I
O
(max)
V
O
V
I
ǒ1 *
V
O
V
I
Ǔ
Ǹ
DV
O
+ V
O
1 *
V
O
V
I
L f
ǒ
1
8 C
o
f
) R
ESR
Ǔ
I
RMS(Co)
+ V
O
1–
V
O
V
I
L f
1
2 3
Ǹ
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SLVS432E –SEPTEMBER 2002–REVISED JUNE 2011
OUTPUT CAPACITOR SELECTION
The output capacitor should have a minimum value of 22µF. For best performance, a low ESR ceramic output
capacitor is needed.
For completeness, the RMS ripple current is calculated as:
The overall output ripple voltage is the sum of the voltage spike caused by the output capacitor ESR plus the
voltage ripple caused by charge and discharging the output capacitor:
The highest output voltage ripple occurs at the highest input voltage V
I
.
INPUT CAPACITOR SELECTION
Because the buck converter has a pulsating input current, a low ESR input capacitor is required for best input
voltage filtering and minimizing the interference with other circuits caused by high input voltage spikes. The input
capacitor should have a minimum value of 10 µF and can be increased without any limit for better input voltage
filtering. The input capacitor should be rated for the maximum input ripple current calculated as:
The worst case RMS ripple current occurs at D = 0.5 and is calculated as: I
RMS
= I
O
/2. Ceramic capacitors have a
good performance because of their low ESR value and they are less sensitive to voltage transients compared to
tantalum capacitors. Place the input capacitor as close as possible to the input pin of the IC for best
performance.
Table 4. Capacitors
MANUFACTURER PART NUMBER SIZE VOLTAGE CAPACITANCE TYPE
JMK212BJ106MG 0805 6.3 V 10 µF Ceramic
JMK316BJ106ML 1206 6.3 V 10 µF Ceramic
JMK316BJ226ML 1206 6.3 V 22 µF Ceramic
Taiyo Yuden
LMK316BJ475ML 1206 10 V 4.7 µF
(1)
Ceramic
EMK316BJ475ML 1206 16 V 4.7 µF
(1)
Ceramic
EMK325BJ106KN-T 1210 16 V 10 µF Ceramic
Kemet C1206C106M9PAC 1206 6.3 V 10 µF Ceramic
C2012X5R0J106M 0805 6.3 V 10 µF Ceramic
TDK C3216X5R0J226M 1206 6.3 V 22 µF Ceramic
C3216X5R1A106M 1206 10 V 10 µF Ceramic
(1) Connect two in parallel.
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