bd6581gu ROHM Co. Ltd., bd6581gu Datasheet - Page 10

• Manufacturer Part Number: bd6581gu
• Description: White Backlight Led Driver
• Manufacturer: ROHM Co. Ltd.

●Operating of the Application Deficiency
●Control Signal input Timing
BD6581GU
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www.rohm.com
1) When 1 LED or 1parallel OPEN during the operating
2) When LED short-circuited in the plural
3) When Schottky diode came off
4)When over current detection resistor came off
In case you input control signs, such as RSTB, PWMPOW, and PWMDRV, in the condition that the standup of supply voltage
(VBAT) is not completed, be careful of the following point.
There is no timing limitation at each input signal of RSTB, PWMPOW and PWMDRV.
If each control sign changes into a condition lower than VBAT in (1) and (2), it goes via the ESD custody diode by the side of
VBAT of each terminal.
the entrance current to the terminal exceeds 50mA, it has possibility to damage the LSI. In order to avoid this condition, as
shown in the above figure, please insert about 220ohm in a signal line, and apply current qualification. Please confirm an
internal pull down resistor in the block diagram and electrical property of P.5.
(Example 2)
In case of FAILSEL=L, the LED parallel which became OPEN isn't lighting, but other LED parallel is lighting.
At that time, output boosts up to the over voltage protection voltage 44.7V so that LED terminal may be 0V or it boost to
the output voltage that LED terminal voltage becomes LED terminal over voltage protection 11.5V or it becomes the output
voltage restricted by the over current limit.
In case of FAILSEL=H, boost stops when LED becomes OPEN and all LED turns off the lights.
In case of FAILSEL=L, all LED is turned on unless LED terminal voltage is LED terminal over voltage protection of more
than 11.5V. When it was more than 11.5V only the line which short-circuited is turned on normally and LED current of other
lines fall or turn off the lights. In case of FAILSEL=H, boost stops at more than 11.5V and all LED turns off the lights.
Regardless of FAILSEL, all LED isn't turned on. Also, IC and a switching transistor aren't destroyed because boost
operating stops by the Schottky diode coming off protected function.
Regardless of FAILSEL, all LED isn't turned on. Because the resistance of 100kΩ is between SENSP and SENSN terminal,
over current protection works instantly and LED current can't be flow.
①Input each control signal after VBAT exceeds 2.7V.
②Please do not input each control sign until VBAT exceeds HI voltage of RSTB, PWMPOW, and PWMDRV.
③When you input RSTB during the standup of VBAT and HI voltage is inputted into PWMPOW,
VBAT
PWMPOW
RSTB
PWMDRV
In case of, VIN=12.0V, L=4.7µH, fsw=1MHz, VOUT=39V, IOUT=80mA, Efficiency=85%
Ipeak = (12.0V / 4.7µH) x (1 / 1MHz) x (1-(12V / 39V)) =1.77A
Iave = (39V x 80mA / 12.0V) / 85% = 0.31A
Ton = (0.31A x (1-12 V / 39V) x (1 / 1MHz) x ( 4.7µH /12 V) x 2)
(1-VIN/VOUT) x (1/fsw)=0.69µs > Ton
Peak current = 12V/4.7µH x 0.41µs = 1.05A
*When too large current is set, output overshoot is caused, be careful enough because it is led to break down of the IC
in case of the worst.
please give the standup time to stable voltage as Min.100µs 2.7V of VBAT.
Figure.31 control Signal timing
VREG
DC/DC VOUT
2.7V
①
5V
②
③
A power supply is supplied to VBAT and there is a possibility of malfunctioning. Moreover, when
Min. 100μs
5V
10/26
Figure.32 Voltage with a control sign higher than VBAT
Example corresponding to application of conditions
1/2
= 0.41µs
5V
220Ω
PIN
GND
VBAT
0V
Rin
2010.03 - Rev.A
Technical Note