S3F84P4_AN_REV0.00 (PRELIMINARY SPEC) 2 HARDWARE IMPLEMENTATION
2.2 COMPONENTS SELECTION
Assume the following two conditions:
( 1 ) 3.5 0.35 3.85
OFWFW

V V I ohm V 

5
I

VV

If non-divided system clock is selected as the clock source of the 6+6 PWM, its base frequency
is 6125
2
OSC
fKHz.
2.2.1 SELECT THE INDUCTANCE (L1) FOR THE REQUIREMENT OF CURRENT RIPPLE
1
()
IO
P
WM
ripple
D
VV f
V
LII
T


13.85
(5 3.85) 7.084
5 125
ripple
LI K
 
Therefore, 20% current ripple means .
1100LuH
2.2.2 SELECT THE CAPACITANCE (C2) FOR THE REQUIREMENT OF VOLTAGE RIPPLE
To reduce the voltage ripple and power loss, a capacitor with small ESR like Tantalum Capacitor should be
chosen as C2. When ESL and ESR are negligible, then,
2
P
WM
ripple

I

f

CV

20.35*0.2 0.56
125
ripple

CV K


Therefore, 1% voltage ripple means .
247CuF
The freewheeling diode should be a Schottky diode, as the system requires low turn-on voltage and fast switching.
S
amsun
g
Con
f
idential
12