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BD6583MUV-A

White Backlight LED Driver for Medium to Large LCD Panels (Switching Regulator Type)

ROHM Semiconductor 

BD6583MUV-A

Technical Note

(Example 2)

In case of, VIN=12.0V, L=4.7µH, fsw=1MHz, VOUT=39V, IOUT=80mA, Efficiency=85%

Ipeak = (12.0V / 4.7µH) × (1 / 1MHz) × (1-(12V / 39V)) =1.77A

Iave = (39V × 80mA / 12.0V) / 85% = 0.31A

Ton = (0.31A × (1-12 V / 39V) × (1 / 1MHz) × ( 4.7µH /12 V) × 2)1/2 = 0.41µs

(1-VIN/VOUT) × (1/fsw)=0.69µs > Ton

Peak current = 12V/4.7µH × 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.

●Operating of the application deficiency

1)When 1 LED or 1parallel OPEN during the operating

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.

2)When LED short-circuited in the plural

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.

3)When Schottky diode came off

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.

4)When over current detection resistor came off

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.

●Control signal input timing

2.7V 5V

VBAT

2

Min. 100µs

5V

1

RSTB

3

PWMPOW

PWMDRV

VREG

DC/DC VOUT

0V

VBAT

220Ω

5V

PIN

Rin

GND

Fig.31 Control signal timing

Fig.32 Voltage with a control sign higher than VBAT

Example corresponding to application of conditions

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.

①Input each control signal after VBAT exceeds 2.7V.

②Please do not input each control sign until VBAT exceeds H voltage of RSTB, PWMPOW, and PWMDRV.

③When you input RSTB during the standup of VBAT and H voltage is inputted into PWMPOW, please give the standup time

to stable voltage as Min.100µs 2.7V of VBAT.

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. A power supply is supplied to VBAT and there is a possibility of malfunctioning. Moreover, when 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 220Ω 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.

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

10/26

2011.06 - Rev.C

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