rt9205 Richtek Technology Corporation, rt9205 Datasheet - Page 11

• Manufacturer Part Number: rt9205
• Description: Dual Regulators - Synchronous Buck Pwm Dc-dc And Linear Controller
• Manufacturer: Richtek Technology Corporation

Inductor Selection
The RT9205/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
Table 1
*Refer to Sanyo low ESR series (CE, DX, PX.....)
The suggested L and C are as follows:
2μH with ≥ 1500μF C
5μH with ≥ 1000μF C
DS9205/A-09 October 2008
IL
T
V
Inductor
1000μF (ESR=53mΩ)
1500μF (ESR=33mΩ)
3000μF (ESR=21mΩ)
ON
OUT RIPPLE
RIPPLE
= 3.33
0 A
4 V
2 V
0 V
OUT
=
ripple is
(5V - V
V
COUNT = 1
×
OUT
= IL
V
5V
OUT
L
RIPPLE
T0
OUT
T1
)
OUT
OUT
×
×
Figure 5
T
ESR
COUNT = 2
ON
OVERLOAD
APPLIED
100mV
T2
62mV
40mV
2μH
TIME
3.3V
IN
OUT
COUNT = 3
= 5V, step-down
40mV
25mV
16mV
5μH
T3
at VIN = 5V
110mV
68mV
43mV
2μH
2.5V
44mV
28mV
18mV
5μH
i
i
L
V
Q
i
V
D
I
L
93mV
58mV
37mV
C.C.M.
2μH
T
ON
1.5V
T
Q
V
S
I
37mV
23mV
15mV
- V
T
5μH
OFF
uI
O
D
L
Figure 6
- V
O
L
C
RT9205/A
uQ
www.richtek.com
R
V
I
I
O
L
I
D
Q
= I
O
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