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RN5RG Datasheet(PDF) 6 Page - RICOH electronics devices division

Part No. RN5RG
Description  VOLTAGE REGULATOR WITH EXTERNAL POWER TRANSISTOR 
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Maker  RICOH [RICOH electronics devices division]
Homepage  http://www.ricoh.com
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RN5RG Datasheet(HTML) 6 Page - RICOH electronics devices division

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RN5RG
5
OPERATION
VOUT
GND
GND
Vref
VDD
External PNP Transistor
EXT
OUT
IN
RA
RB
CE
+
2
4
3
Error
Amplifier
5
1
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
VOUT
CL
VIN
External PNP Transistor
EXT
OUT
R1
R2
3
4
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.
1.External PNP Transistor
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
2.Base Resistor R2
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 10k
Ω 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.
3.Phase Compensation


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