2 components selection, Samsung confidential – Samsung S3F84A5 User Manual
Page 12
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
O
FW
FW
V
V
I
ohm
V
5
I
V
V
If non-divided system clock is selected as the clock source of the 6+6 PWM, its base frequency
is
6
125
2
OSC
f
KHz
.
2.2.1 SELECT THE INDUCTANCE (L1) FOR THE REQUIREMENT OF CURRENT RIPPLE
1
(
)
I
O
PWM
ripple
D
V
V
f
V
L
I
I
T
1
3.85
(5 3.85)
7.084
5 125
ripple
L
I
K
Therefore, 20% current ripple means
.
1
100
L
u
H
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
PWM
ripple
I
f
C
V
2
0.35* 0.2
0.56
125
ripple
C
V
K
Therefore, 1% voltage ripple means
.
2
47
C
u
F
The freewheeling diode should be a Schottky diode, as the system requires low turn-on voltage and fast switching.
Samsung Confidential
12