Diodes AP6015 - Manual (Page 15)

AP6015
High Efficiency Step-Down Low Power DC-DC Converter
AP6015 Rev. 3 15 of 18 FEBRUARY 2009
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„ Input Capacitor Selection
Though there is no special requirement for the ESR (Equivalent Series Resistance) of the input capacitor, due
attention should be paid to the tolerance and temperature coefficient of the capacitor used. A 10uF or larger
capacitance is required between the PVCC and the GND pins. The input capacitor should be placed as
close as possible to the PVCC pin in order to achieve good overall system performance.
„ Output Capacitor Selection
Ripple at the voltage output pin is caused by the charge-and-discharge of the output capacitor. For the best
performance, a low ESR output capacitor should be used. The equation below demonstrates how the size of
the ripple can be calculated.
)
8
1
( )
8
1
(
) ( 1
ESR
f C
I ESR
f C f L
V
V
V V
O
L
O
CC
O
O O
+
Ч Ч
Ч Δ = +
Ч Ч
Ч
Ч
−
Ч = Δ
Where:
△Vo= Output voltage ripple
L = Inductor value
f = Switching frequency (1MHz typical)
△I
L
= Peak-to-peak inductor ripple current
Application Information
(Continued)