Datasheet

Application information PM6644
22/35 Doc ID 023203 Rev 1
.
3.1.2 Input capacitor selection
In a buck topology converter the current that flows into the input capacitor is a pulsed current
with zero average value. The input RMS current of the switching regulator can be roughly
estimated as follows:
Equation 11
where D is the duty cycles and I
LOAD
(max.) is the maximum load current of the switching
regulator. The input capacitor should be chosen with an RMS rated current higher than the
maximum RMS current given by the formula.
Tantalum capacitors are good in terms of low ESR and small size, but they can occasionally
burn out if subjected to very high current during the charge.
Ceramic capacitors usually have a higher RMS current rating with smaller size and they
remain the best choice. In battery-powered applications, a 1-2.2 µF input ceramic capacitor
can be enough.
Tabl e 11 shows an example of ceramic capacitor part numbers.
3.1.3 Output capacitor selection
The controller can work with ceramic or tantalum output capacitors.
The selection of the output capacitor impacts on the stability of the controller:
Equation 12
Equation 13
Table 10. Inductor part number
Manufacturer Part number
Inductance
(µH)
DCR (Ω)
RMS current
(A)
(1)
1. 40 °C temperature rise.
Saturation
current (A)
(2)
2. 20% inductance drop.
Coilcraft EPL3015-333ML 33 0.989 0.59 0.32
Coilcraft LPS3314-333ML 33 0.92 0.58 0.38
Coilcraft MSS5121-333ML 33 0.48 0.76 0.64
Table 11. Input capacitor part numbers
Manufacturer Part number Capacitor value (µF) Rated voltage
TAYIO YUDEN TMK212BJ225MG-T 2.2 25
I
CinRMS
I
LOAD
max()D1D–()⋅⋅=
C
OUT
18 α⋅
2 Π f
sw
k⋅⋅ ⋅
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α
0.9V
V
OUT
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