Technical Note

11/26

www.rohm.com

2011.06 - Rev.C

© 2011 ROHM Co., Ltd. All rights reserved.

BD6583MUV-A

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How to select the number of LED lines of the current driver

When the number of LED lines of the current driver is reduced, the un-select can be set the matter that the unnecessary

LED1 ~ 6 terminal is connected to GND. When it uses with 4 lines and so on, it can correspond to it by connecting 2

unnecessary lines to GND.

RSTB is used as a power supply of this decision circuit. The select of the terminal is judged, It has no relation to the logic of

PWMPOW and PWMDRV and it isn't judged an unnecessary LED line even if it is connected to GND when it is judged a

necessary terminal once. This information can be reset by setting RSTB at 0V.

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Start control and select LED current driver

BD6583MUV-A can control the IC system by RSTB, and IC can power off compulsory by setting 0.2V or below. Also, It

powers on PWMPOW is at more than 1.4V and RSTB is at more than 2.25V.

When RSTB=PWMPOW=H, ISETH current is selected at PWMDRV=H and ISETL current is selected at PWMDRV=L.

The starting current in PWMDRV=L sets OFF second time rise of PWMDRV and it becomes 0mA setting after that.

After RSTB sets L once, the starting current can be flowed again by changing it to H.

RSTB

PWMPOW

PWMDRV

IC

LED current

H

L

L

Off

OFF

H

H

L

On

Starting current decided with ISETL

H

L

H

Off

OFF

H

H

H

On

Current decided with ISETH

L

L, H

L, H

Off

OFF

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Attendance point of the restriction resistance input to RSTB

When the restriction resistance is input to RSTB, it is necessary to consider the input current of RSTB.

The input current of RSTB changes that depending on the power-supply voltage and the temperature reference to Fig.33.

Because the temperature characteristic of the input current is shown in Fig.33, please choose resistance for which the

voltage of the terminal can be guaranteed to 2.1V or more.

And, it has the margin in the decision of resistance, and please confirm and make sure it is no problem in a real application.

The decision example of restriction resistance

1.When use the current driver of 6 parallel

2.9V(to RSTB power-supply) - restriction resistance value × 124μA(100 ℃ input current) > 2.1V

restriction resistance value < (2.9-2.1)/124μA=6.45kΩ

2.When use the current driver of 3 parallel

2.9V(to RSTB power-supply) - restriction resistance value × 430μA(100 ℃ input current) > 2.1V

restriction resistance value < (2.9-2.1)/430μA=1.86kΩ

Fig .33

Fig .34 RSTB terminal voltage-RSTB inflow current

(At the time of the current driver 6 lines use)

Limit resistor

RSTB

terminal

BD6583MUV-A

RSTB inflow current

Power supply

for RSTB

50

100

150

200

250

2.1

2.4

2.7

3

3.3

3.6

RSTB[V]

-30 ℃

+25 ℃

+80 ℃

+100 ℃