Datasheet

NCP1421
http://onsemi.com
12
From the previous calculations, you need at least 18.75
F in order to achieve the specified ripple level at the
conditions stated. Practically, a capacitor that is one level
larger is used to accommodate factors not taken into
account in the calculations. Therefore, a capacitor value of
22 F is selected. The NCP1421 is internally compensated
for most applications, but in case additional compensation
is required, the capacitor C4 can be used as external
compensation adjustment to improve system dynamics.
In order to provide an easy way for customers to select
external parts for NCP1421 in different input voltage and
output current conditions, values of inductance and
capacitance are suggested in Figure 27, 28 and 29.
0
2
4
6
8
10
12
14
16
1.4
1.8 2.0 2.2
2.4
2.6 2.8 3.0
Figure 27. Suggested Inductance of V
OUT
= 3.3 V Figure 28. Suggested Inductance of V
OUT
= 5.0 V
Figure 29. Suggested Capacitance for Output Capacitor
1.6
INPUT VOLTAGE (V)
INDUCTOR VALUE (H)
I
OUT
= 500 mA
0
3
6
9
12
15
18
21
1.6
2.2 2.5 2.8 3.1 3.4 3.7 4.0
1.9
INPUT VOLTAGE (V)
INDUCTOR VALUE (H)
I
OUT
= 500 mA
OUTPUT CURRENT (mA)
CAPACITOR VALUE (F)
CAPACITOR ESR (m)
V
OUT−RIPPLE
= 45 mV
V
OUT−RIPPLE
= 50 mV
V
OUT−RIPPLE
= 40 mV
25
33
50
100
40
35
30
25
20
15
10
5
0
200 250 300 350 400 450 500 550 600
Table 1. Suggestions for Passive Components
Output Current Inductors Capacitors
500 mA Sumida CR43, CR54,CDRH6D28 series Panasonic ECJ series
Kemet TL494 series
250 mA Sumida CR32 series Panasonic ECJ series
Kemet TL494 series