RT9204CS datasheet(9/14 Pages) RICHTEK

9 / 14 page

Preliminary

RT9204

DS9204-00 February 2002

www.richtek-ic.com.tw

Fig. 3

Shutdown

Pulling high the SD pin by a small single transistor

can shutdown the RT9204 PWM controller as shown

in typical application circuit. Normally SD pin can be

floating because an internal 40

µA current source will

pull low the SD shutdown pin voltage.

Applications Information

Inductor Selection

The RT9204 was designed for VIN = 5V, step-down

application mainly. Fig.4 shows the typical topology

and waveforms of step-down converter.

The ripple current of inductor can be calculated as

follows:

ILRIPPLE = (5V - VOUT)/L

× TON

Because operation frequency is fixed at 600kHz,

TON = 3.33

× VOUT/5V

The VOUT ripple is

VOUT RIPPLE = ILRIPPLE

× ESR

ESR is COUT capacitor equivalent series resistor

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

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

The suggested L and C are as follows:

µH with ≥ 1500µF COUT

µH with ≥ 1000µF COUT

Table 1

Fig.4

VOUT

3.3V

2.5V

1.5V

Inductor

µH5µH2µH5µH2µH5µH

1000

µF (ESR = 53mΩ)

100mV

40mV

110mV

44mV

93mV

37mV

1500

µF (ESR = 33mΩ)

62mV

25mV

68mV

28mV

58mV

23mV

3000

µF (ESR = 21mΩ)

40mV

16mV

43mV

18mV

37mV

15mV

TON

TOFF

VI - VO

- VO

IL = IO

µQ

µIL

C.C.M.

T0T1

TIME

COUNT = 1 COUNT = 2 COUNT = 3

OVERLOAD

APPLIED

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