RT9203 RICHTEK [Richtek Technology Corporation], RT9203 Datasheet - Page 12

• Manufacturer Part Number: RT9203
• Description: Dual Regulators - Synchronous Buck PWM DC-DC and Linear Controller
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9203/A
Inductor Selection
The RT9203/A was designed for V
application mainly. Figure 6 shows the typical topology
and waveforms of step-down converter.
The ripple current of inductor can be calculated as follows:
Because operation frequency is fixed at 300kHz,
The V
ESR is the equivalent series resistor of output capacitor
Table 1 shows the ripple voltage of V
*Refer to Sanyo low ESR series (CE, DX, PX......)
The suggested L and C are as follows:
2 H with
5 H with
www.richtek.com
12
Inductor
1000 F (ESR=53m )
1500 F (ESR=33m )
3000 F (ESR=21m )
Table 1
IL
T
V
ON
OUT RIPPLE
RIPPLE
0 A
4 V
2 V
0 V
OUT
= 3.33
ripple is
=
V
COUNT = 1
1500 F C
1000 F C
(5V - V
OUT
= IL
V
T0
5V
OUT
L
RIPPLE
T1
OUT
OUT
OUT
)
Figure 5
COUNT = 2
T
ESR
OVERLOAD
ON
APPLIED
100mV
T2
62mV
40mV
2 H
TIME
3.3V
IN
OUT
COUNT = 3
= 5V, step-down
25mV
16mV
40mV
5 H
T3
at V
IN
= 5V
110mV
68mV
43mV
Preliminary
2 H
2.5V
44mV
28mV
18mV
5 H
C.C.M
V
i
i
V
Q
I
L
i
D
L
93mV
58mV
37mV
2 H
T
ON
1.5V
Q
T
S
V
37mV
23mV
15mV
I
5 H
D
T
- V
OFF
mI
O
Figure 6
L
- V
L
O
DS9203/A-10 March 2007
C
uQ
R
V
O
I
I
I
L
Q
D
= I
O