R1152N Datasheet, PDF (16/21 Pages) RICOH electronics devices division – High Input Voltage Tolerant Boost Voltage Regulator

R1152N
APPENDIX
• Technical Notes on Output Voltage Setting
EXT
IIC
VOUT
I2
RIC
GND
I3
PNP Tr
OUT
R2
VOUT2
R3 2.5V
The output voltage of regulator with R1152N025x may be adjustable for any output voltage between its 2.5V
reference and VDD setting level. An external pair of resistors is required, as shown above figure.
The complete equation for the output voltage is described step by step as follows;
I2=IIC+I3 ....................................................................................................................................... (1)
I3=2.5/R3 ...................................................................................................................................(2)
Thus,
I2= IIC+2.5/R3 ..............................................................................................................................(3)
Therefore,
VOUT=2.5+R2×I2.........................................................................................................................(4)
Put Equation (3) into Equation (4), then
VOUT=2.5+R2×(IIC+2.5/R3)
=2.5×(1+R2/R3)+R2×IIC .....................................................................................................(5)
In 2nd term, or R2×IIC will produce an error in VOUT.
In Equation(5),
IIC=2.5/RIC ..................................................................................................................................(6)
R2×IIC=R2×2.5/RIC
=2.5×R2/RIC.................................................................................................................. (7)
For better accuracy, choosing R2 (<<RIC) reduces this error.
∗RIC is approximately 1.1MΩ.
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