R1155 Datasheet, PDF (11/26 Pages) RICOH electronics devices division – 150 mA 24 V Input High Voltage Regulator

R1155x
NO.EA-270-150702
Adjustable Output Voltage Type Setting (R1155x001C)
The output voltage of the R1155x001C can be adjusted up to 23 V by using the external divider resistors (R1,
R2). The resistance value for R2 should be set to 24 MΩ or less. By using the following equations, the output
voltage can be determined. VFB voltage which is fixed inside the IC is described as setVFB. setVFB is 2.5 V.
When using the R1155x001C with 2.5 V, please connect the VOUT pin to the VFB pin.
V_OUT
R1 I1
V_FB
R_IC
GND
I_IC
V_OUT
R2 _{I2 setVFB}
Output Voltage Adjustment Using External Divider Resistors
I1 = IIC + I2.......................................................................................................................................(1)
I2 = setVFB / R2................................................................................................................................(2)
Thus,
I1 = IIC + setVFB / R2......................................................................................................................... (3)
Therefore,
VOUT = setVFB + R1 x I1.................................................................................................................... (4)
Insert Equation (3) into Equation (4), so
VOUT = setVFB + R1 x (IIC + setVFB / R2)
= setVFB x (1+ R1 / R2) + R1 x IIC ............................................................................................ (5)
In Equation (5), R1xIIC is the error-causing factor in VOUT.
As for IIC,
IIC = setVFB / RIC…………………………………………………………………………………………………………………………………………………(6)
Therefore, the error-causing factor R1x IIC can be described as follows.
R1 x IIC = R1 x setVFB / RIC
= setVFB  R1 / RIC .............................................................................................................. (7)
For better accuracy, choosing R1 (<<RIC) reduces this error.
Without the error-causing factor R1x IIC, the output voltage can be calculated by the following equation.
VOUT = setVFB  ((R1 + R2) / R2) ..................................................................................................... (8)
RIC of the R1155x001C is approximately Typ.8.4 MΩ (Ta = 25°C, guaranteed by Design Engineering).
RIC could be affected by the temperature, therefore evaluate the circuit taking the actual conditions of use into
account when deciding the resistance values for R1 and R2.
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