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Output Capacitor Selection
L x ¦
1-
x
V
I
2x 3Ö
I =V x
(RMSCout) O
V
O
1
(7)
L x ¦
1-
+ESR
()
V
I
8xC x
O
¦
DV =V x
O O
V
O
1
x
(8)
Input Capacitor Selection
TPS65050, TPS65051, TPS65052
TPS65054, TPS65056
SLVS710A – JANUARY 2007 – REVISED AUGUST 2007
Table 4. Tested Inductors
Inductor Type Inductor Value Supplier
LPS3010 2.2 μ H Coilcraft
LPS3015 3.3 μ H Coilcraft
LPS4012 2.2 μ H Coilcraft
VLF4012 2.2 μ H TDK
The advanced Fast Response voltage mode control scheme of the two converters allow the use of small ceramic
capacitors with a value of 22- μ F (typical), without having large output voltage undershoots and overshoots during
heavy load transients. Ceramic capacitors having low ESR values result in lowest output voltage ripple, and are
recommended.
If ceramic output capacitors are used, the capacitor RMS ripple current rating always meets the application
requirements. For completeness, the RMS ripple current is calculated as:
At nominal load current, the inductive converters operate in PWM mode, and the overall output voltage ripple is
the sum of the voltage spike caused by the output capacitor ESR plus the voltage ripple caused by charging and
discharging the output capacitor:
Where the highest output voltage ripple occurs at the highest input voltage V
I
.
At light load currents, the converters operate in Power Save Mode and the output voltage ripple is dependent on
the output capacitor value. The output voltage ripple is set by the internal comparator delay and the external
capacitor. The typical output voltage ripple is less than 1% of the nominal output voltage.
Because of the nature of the buck converter having 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 converters need a ceramic input capacitor of 10 μ F. The input capacitor can be increased
without any limit for better input voltage filtering.
Table 5. Possible Capacitors
Capacitor Value Size Supplier Type
2.2 μ F 0805 TDK C2012X5R0J226MT Ceramic
2.2 μ F 0805 Taiyo Yuden JMK212BJ226MG Ceramic
10 μ F 0805 Taiyo Yuden JMK212BJ106M Ceramic
10 μ F 0805 TDK C2012X5R0J106M Ceramic
10 μ F 0603 Taiyo Yuden JMK107BJ106MA Ceramic
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