Technical Note

8/26

www.rohm.com

2011.06 - Rev.C

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

BD6583MUV-A

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Description of Functions

1) PWM current mode DC/DC converter

While BD6583MUV-A is power ON, the lowest voltage of LED1, 2, 3, 4, 5, 6 is detected, PWM duty is decided to be

0.5Vand output voltage is kept invariably. As for the inputs of the PWM comparator as the feature of the PWM current

mode, one is overlapped with error components from the error amplifier, and the other is overlapped with a current sense

signal that controls the inductor current into Slope waveform to prevent sub harmonic oscillation. This output controls

external Nch Tr via the RS latch. In the period where external Nch Tr gate is ON, energy is accumulated in the external

inductor, and in the period where external Nch Tr gate is OFF, energy is transferred to the output capacitor via external

SBD.BD6583MUV-A has many safety functions, and their detection signals stop switching operation at once.

2) Soft start

BD6583MUV-A has soft start function.

The soft start function prevents large coil current.

Rush current at turning on is prevented by the soft start function.

After RSTB is changed L H, when PWMPOW is changed L H, soft start becomes effective for within 1ms and soft start

doesn't become effective even if PWMPOW is changed L H after that.

And, when the H section of PWMPOW is within 1ms, soft start becomes invalid when PWMPOW is input to H more than

three times. The invalid of the soft start can be canceled by making RSTB  L.

3) FAILSEL pin

When the error condition occurs, boost operating is stopped by the protection function, and the error condition is avoided.

On that occasion, the way to stop of boost operating by the protection function can be selected with FAILSEL pin. Details

are as shown in Fig.29, 30.

After power ON, when the protection function is operating under about 1ms have passed, the stop state of the boost

operating can be held through FAILSEL is H, the stop state can reset through RSTB is L.

And, boost operating is stopped when the protection function is operating through FAILSEL is L, but when the protection

function becomes un-detect, boost operating is started again. It never keeps holding the stop state of boost operating.

Object of protect function is as shown below.

・

Over-voltage protection

・

External SBD open detect

・

Thermal shutdown

・

LED terminal over-voltage protection

・

Over current limit

Fig.29 FAILSEL operating description

Fig.30 FAILSEL=H light off control

In PWM control by PWMDRV can’t use this function.

When it is off over 10ms on PWM control by PWMPOW using this function, it may be stopped the boost

operating as over current protection work at off on PWMPOW=L.

RSTB

PWMDRV

Coil current

FAILSEL

function

invalid

valid

< When it is off on PWMPOW>

Output

voltage

PWMPOW

RSTB

PWMDRV

PWMPOW

invalid

Output

voltage

Coil current

FAILSEL

function

< When it is off on RSTB>

about 1ms

un-operating range

FAILSEL

RSTB

Protection

function

detection

Boost

operating

normal operating

off

boost stop

“H”

off

normal operating

un-detection

un-detection

<FAILSEL=H>

about 1ms

un-operating range

FAILSEL

RSTB

Protection

function

normal operating

off

un-detection

detection

normal

operating

boost stop

off

normal

“L”

un-detectio

<FAILSEL=L>

Boost

operating