RN5RG Просмотр технического описания (PDF) - RICOH Co.,Ltd.

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RN5RG

VOLTAGE REGULATOR WITH EXTERNAL POWER TRANSISTOR

RICOH Co.,Ltd. 

OPERATION

External PNP Transistor

IN

2

VDD

Error

Amplifier

EXT

4

VOUT

3

RA

OUT

+

–

RB

Vref

5

CE

GND GND

1

RN5RG

In these ICs, Output Voltage VOUT is detected by

Feed-back Registers RA, RB, and the detected Output

Voltage is compared with a reference voltage by Error

Amplifier, so that the base current of External PNP

Transistor is adjusted and Output Voltage VOUT is regu-

lated.

SELECTION GUIDE FOR EXTERNAL COMPONENTS

1.External PNP Transistor

External PNP Transistor

VIN

R1

OUT

R2

EXT

4

3 VOUT

CL

Select External PNP Transistor from the view-

points of output current, input voltage and power dis-

sipation.

Generally External PNP Transistor with low VCE (SAT)

and high hFE is suitable.

2.Base Resistor R2

EXT Pin of these ICs is protected by a current limit circuit from the destruction caused by excess current.

However, since this current limit circuit is provided for the purpose of protecting the IC, use a resistor R2 for the

protection of the External Transistor, although this IC can be operated without such a resistor. It is required that

the resistance of the Resistor R2 be determined with the input voltage, output voltage,output current, tempera-

ture, and the hFE value taken into consideration and the dispersion of these values. Before making such a deter-

mination, check the characteristics by calculating the respective values by using the following formula :

VIN [MIN.] –1.2(V) 0.7(V) IOUT [MAX.]

–

>

R2

R1

hFE

3.Phase Compensation

In these ICs, phase compensation is made for securing stable operation even when the load current is varied.

For this purpose, be sure to use a capacitor CL (tantalum type) with a capacitance of 10µF or more and a resistor

R1 with a resistance of about 10kΩ between the base and the emitter.There may be the case the loop oscillation

takes place when a tantalum capacitor CL with a large ESR is used, so select the CL carefully including the fre-

quency characteristics.

5

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