RT9203GS Ver la hoja de datos (PDF) - Richtek Technology

Número de pieza

componentes Descripción

Fabricante

RT9203GS

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

Richtek Technology 

RT9203/A

Preliminary

COUNT = 1

4V

2V

0V

COUNT = 2 COUNT = 3

OVERLOAD

APPLIED

L

Q

VI

D

C

R VO

C.C.M

TS

0A

T0 T1

T2

T3

TIME

Figure 5

Inductor Selection

The RT9203/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,

VOUT

TON = 3.33 ×

5V

The VOUT ripple is

VOUT RIPPLE = ILRIPPLE × ESR

TON

TOFF

VI - VO

VL

- VO

iL

uQ

mIL

IL = IO

iQ

IQ

iD

ID

Figure 6

ESR is the equivalent series resistor of output capacitor

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

Table 1

VOUT

Inductor

1000µF (ESR=53mΩ)

1500µF (ESR=33mΩ)

3000µF (ESR=21mΩ)

3.3V

2µH

5µH

100mV 40mV

62mV 25mV

40mV 16mV

2.5V

2µH

5µH

110mV 44mV

68mV 28mV

43mV 18mV

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

The suggested L and C are as follows:

2µH with ≥ 1500µF COUT

5µH with ≥ 1000µF COUT

1.5V

2µH

5µH

93mV 37mV

58mV 23mV

37mV 15mV

www.richtek.com

12

DS9203/A-10 March 2007

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