bd9745ekn ROHM Co. Ltd., bd9745ekn Datasheet - Page 20

• Manufacturer Part Number: bd9745ekn
• Description: 7-channel Switching Regulator Controller For Digital Camera
• Manufacturer: ROHM Co. Ltd.

７.) Setting the output voltage.
b. Setting the feed back of CH7
a. Setting for positive to negative converter (CH5).
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.
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.
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.
CH5 output
CH7 output voltage =
CH7 output current =
CH7 Output
Io7
R3
= －
R1+R2
0.4V
R3
Ｒ２
Ｒ１
R2
R2
R1
CH5 output
Fig -14 Setting for Voltage and current of CH7.
ＶＲEF
× VREF （ = 1V ）
R1
R2
× 0.8V
NON5
（Example R3 = 20Ω⇒ Io7 = 20mA）
Vo7
Fig-13 setting for CH5 feed back resistor
INV7I
INV7
（Example R1 =180kΩ, R2=15kΩ⇒Vo7=13V）
REV. D
＋
－
=
0.8V
0.4V
NON is connected to GND .
ERROR AMP5
－
R2
R1
-
+
-
+
ERROR AMP7V
ERROR AMP7I
(Example)
R1 = 20kΩ, R2 = 160kΩ
CH5 output = -8.0V
Priority L
20/21