RT9202B Ver la hoja de datos (PDF) - Richtek Technology

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componentes Descripción

Fabricante

RT9202B

Single Synchronous Buck PWM DC-DC Controller

Richtek Technology 

RT9202B

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.....)

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

L

Q

VL

VI

D

C

R VO

C.C.M

TS

TON

TOFF

VI - VO

Input / Output Capacitor

High frequency/long life decoupling capacitors should be

placed as close to the power pins of the load as physically

possible. Be careful not to add inductance to the PCB

trace, as it could eliminate the performance from utilizing

these low inductance components. Consult with the

manuf acturer of the load on specific decoupling

requirements.

The output capacitors are necessary for filtering output

and stabilizing the close loop (see the PWM loop stability).

For powering advanced, high-speed processors, it is

required to meet with the requirement of fast load

transient, high frequency capacitors with low ESR/ESL

capacitors are recommended.

VL

- VO

Another concern is high ESR induced ripple may trigger

UV or OV protections.

PWM Loop Stability

iL

uQ

IL = IO

The RT9202B is a voltage mode buck controller designed

mIL

for 5V step-down applications. The gain of error amplifier

is fixed at 35dB for simplified design.

The output amplitude of ramp oscillator is 1.75V, the loop

gain and loop pole/zero are calculated as follows :

iQ

IQ

DC loop gain GA =

35dB

×

5

1.75

×

0.8

VOUT

LC filter pole PO = 1

2π LC

iD

Error Amp pole PA = 300kHz

ID

ESR zero ZO =

2π

1

ESRC

The RT9202B Bode plot as shown Figure 6 is stable in

Figure 5

most of application conditions.

DS9202B-03 March 2007

www.richtek.com

11

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