bd6581gu ROHM Co. Ltd., bd6581gu Datasheet - Page 8

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

●Description of Functions
BD6581GU
© 2010 ROHM Co., Ltd. All rights reserved.
www.rohm.com
1) PWM current mode DC/DC converter
2) Soft start
3) FAILSEL pin
<FAILSEL=H>
Protection
operating
FAILSEL
Protection
operating
function
<FAILSEL=L>
FAILSEL
function
While BD6581GU is power ON, the lowest voltage of LED1, 2, 3, 4, 5, 6 is detected, PWM duty is decided to be 0.5V and
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.
BD6581GU has many safety functions, and their detection signals stop switching operation at once.
BD6581GU 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.
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.
Boost
RSTB
RSTB
Boost
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.
“H”
・Over-voltage protection
・External SBD open detect
・Thermal shutdown
・LED terminal over-voltage protection
・Over current limit
off
off
“L”
Fig.29. FAILSEL operating description
un-operating range
un-operating range
normal operating
un-detection
about 1ms
normal operating
un-detectio
about 1ms
detection
detection
boost stop
boost stop
un-detection
un-detection
operating
normal
off
off
normal operating
8/26
normal
< When it is off on PWMPOW>
< When it is off on RSTB>
Coil current
Coil current
PWMPOW
PWMPOW
PWMDRV
PWMDRV
FAILSEL
FAILSEL
function
function
voltage
voltage
Output
Output
RSTB
RSTB
Fig.30. FAILSEL=H light off control
invalid
invalid
2010.03 - Rev.A
Technical Note
valid