BD9745EKN Datasheet, PDF (20/22 Pages) Rohm – Silicon Monolithic Integrated Circuit

７.) Setting the output voltage.
a. Setting for positive to negative converter (CH5).
ＶＲEF
20/21
Ｒ１
NON5
Ｒ２
CH5 output
ERROR AMP5
＋
－
NON is connected to GND .
Fig-13 setting for CH5 feed back resistor
The reference of CH5 Error AMP is internally connected to ground. So the high accuracy regulator can be formed up to set up a resistor
divider to Fig.13, It is recommended that R1 resistance is over 20kΩ, because current ability of VREF is about 100μA.
CH5 output
=－
R2
× VREF （ = 1V ） = －
R2
R1
R1
(Example)
R1 = 20kΩ, R2 = 160kΩ
CH5 output = -8.0V
b. Setting the feed back of CH7
CH7 Output
Vo7
R1
INV7
ERROR AMP7V
R2
Io7
0.8V
Priority L
INV7I
ERROR AMP7I
R3
0.4V
Fig -14 Setting for Voltage and current of CH7.
CH7 has two ERRORAMP whose reference is different. ERROR AMP 7I controls constant current feed back for LED Back light, and
ERRORAMP7V controls over voltage feed back and constant voltage feedback.
Each ERRORAMP setting shows below formula.
0.4V
CH7 output current =
R3
（Example R3 = 20Ω⇒ Io7 = 20mA）
R1+R2
CH7 output voltage =
× 0.8V
R2
（Example R1 =180kΩ, R2=15kΩ⇒Vo7=13V）
The lower output of two ERRAMP controls the DC/DC output. There fore, if it is used only one ERRORAMP, other ERRORAMP input must
be shorted to GND.
REV. D