RN5RG50A Ver la hoja de datos (PDF) - RICOH Co.,Ltd.
Número de pieza
componentes Descripción
Lista de partido
RN5RG50A Datasheet PDF : 10 Pages
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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, the output voltage VOUT is detected by
feed-back registers RA, RB, and the detected the output
voltage is compared with a reference voltage by error
Amplifier, so that the base current of an external PNP
transistor is adjusted and the output voltage VOUT is reg-
ulated.
SELECTION GUIDE FOR EXTERNAL COMPONENTS
1.External PNP Transistor
External PNP Transistor
VIN
R1
OUT
R2
EXT
4
3 VOUT
CL
Select an 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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