BD6581GU-E2 Datasheet, PDF (15/35 Pages) Rohm – 6-Channel White LED Driver for up to 72 LEDs

BD6581GU
Datasheet
˔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 to 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.
˔Start Control and Select LED Current Driver
BD6581GU 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
1
0
0
Off OFF
1
1
0
On Starting current decided with ISETL
1
0
1
Off OFF
1
1
1
On Current decided with ISETH
0
0, 1
0, 1
Off OFF
˔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 Figure 30.
Because the temperature characteristic of the input current is shown in Figure 30, 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 valueʷ124µA(100ˆ input current) ʼ 2.1V
restriction resistance valueʻ(2.9-2.1)/124ЖA=6.45kΩ
2. When use the current driver of 3 parallel
2.9V(to RSTB power-supply) - restriction resistance value×430μA(100ˆ input current) ʼ 2.1V
restriction resistance valueʻ(2.9-2.1)/430μA=1.86kΩ
250
200
+100ˆ
+80ˆ
+25ˆ
BD6581GU
150
Power supply
Limit resistor
RSTBç
for RSTB
terminal
100
-30ˆ
RSTB inflow current
Figure 30.
50
2.1 2.4 2.7 3
RSTB[V]
3.3 3.6
Figure 31. RSTB terminal voltage-RSTB inflow current
(At the time of the current driver six lines use)
In addition, the selection number of parallel number of the current driver is changed, the power-supply current of RSTB will
be increased. Because the maximum value of the consumption current at the RSTB=2.1V is indicated in the following Table
1, be careful enough when you calculate the restriction resistance.
Table. the use parallel number of current driver at RSTB=2.1V , 100ˆ vs. RSTB input current
Parallel numbers used for current driver
RSTB input current
6
0.12mA
5
0.23mA
4
0.33mA
3
0.43mA
2
0.53mA
1
0.63mA
0
0.74mA
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TSZ22111ŋ15ŋ001
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TSZ02201-0G3G0C400170-1-2
03.Dec.2012 Rev.001