Technical Note

9/12

BD9206EFV

www.rohm.com

2009.07 - Rev.A

© 2009 ROHM Co., Ltd. All rights reserved.

●The calculation of electric power consumption for IC and the deciding method of external resistance value

Electric power consumption of IC is decided with formula below.

P(N)=ICC*VCC+[(Vo-RL*ILED)-(Vf+⊿Vf+⊿VfT)*M]*N*ILED ・・・・①

ICC

IC Consumed electric

current

VCC

Input voltage

Vf

LED Vf

voltage

（normal temperature typ）

⊿Vf

LED Vf Variation

⊿VfT

LED Vf Temperature

variation

M

Stage number around

LED 1 line

N

LED line number

ILED

LED Constant current

value

Vo

Voltage OF LED anode

side

RL

external resistance

(external loss)

Please insert the heat-radiation resistor RL in order to decrease the heat radiation at the IC.

If the value of RL is made to be larger, then the heat radiation of the IC is decreased, but if the terminal voltage VLED of the

LED driver is less than 0.6V, then the constant current operation becomes impossible, therefore please set the RL in such a way

that the following expression is met:

VLED=Vo-（Vf+⊿Vf+⊿VfT）*M-RL*ILED>0.6V

Please set the ILED and RL in such a way that the relational expressions ① & ② are met.

Moreover, the permissible loss of the package is as shown in the following graph.

Vo

＊M

＊N

ILED

RL

：

：

：

：

：

：

：

：

：

：

HT SS OP- B2 0 Pd

1. 0 0

2. 3 0

3. 20

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0

2 5

5 0

75

10 0

12 5

1 50

周囲温度Ta(℃)

①：1層基板　　　　

(表層放熱銅箔：

0mm2

②：2層基板　　　　

(表裏層放熱銅箔：

4900mm2)

③：4層基板　　　　

(全層放熱銅箔：

4900mm2

①

②

③

Fig..9

Fig..10

①1layer baseplate

copper foil on surface

：

Omm2）

Temperature around Ta

（℃）

②2layer base―plate

copper foil on Inside

and outside layer

：

4900mm2)

③4layer base―plate

copper foil on whole

layer

：4900mm2）