RT9205A Ver la hoja de datos (PDF) - Richtek Technology

Número de pieza

componentes Descripción

Fabricante

RT9205A

Dual Regulators - Synchronous Buck PWM DC-DC and Linear Controller

Richtek Technology 

Preliminary

COUNT = 1

4V

2V

0V

COUNT = 2 COUNT = 3

OVERLOAD

APPLIED

Q

VI

D

C.C.M.

TS

RT9205/A

L

C

R VO

0A

T0 T1

T2

T3

TIME

Figure 5

Inductor Selection

The RT9205/A was designed for VIN = 5V, step-down

application mainly. Figure 6 shows the typical topology

and waveforms of step-down converter.

The ripple current of inductor can be calculated as follows:

(5V - VOUT)

ILRIPPLE =

× TON

L

Because operation frequency is fixed at 300kHz,

VL

iL

TON TOFF

VI - VO

- VO

uQ

uIL

iQ

VOUT

TON = 3.33 ×

iD

5V

The VOUT ripple is

VOUT RIPPLE = ILRIPPLE × ESR

ESR is the equivalent series resistor of output capacitor

Figure 6

Table 1 shows the ripple voltage of VOUT at VIN = 5V

Table 1

VOUT

3.3V

2.5V

Inductor

2µH

5µH

2µH

5µH

1000µF (ESR=53mΩ) 100mV 40mV 110mV 44mV

1500µF (ESR=33mΩ)

62mV 25mV 68mV 28mV

3000µF (ESR=21mΩ)

40mV 16mV 43mV 18mV

*Refer to Sanyo low ESR series (CE, DX, PX.....)

1.5V

2µH

5µH

93mV 37mV

58mV 23mV

37mV 15mV

The suggested L and C are as follows:

2µH with ≥ 1500µF COUT

5µH with ≥ 1000µF COUT

IL = IO

IQ

ID

DS9205/A-08 March 2007

www.richtek.com

11

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