BD9285F Datasheet, PDF (10/39 Pages) Rohm – Boost 1channel white LED driver For large LCDs

BD9285F
Datasheet
PWM1 and PWM2 have the functional difference, and GATE pin outputs only by the logic of PWM1.
This is why only boost operation continues while PWM1=H, PWM2=L. In this case, the adequate confirmation is required
not to be over voltage of the output voltage Vout.
Figure 11. PWM pin function
○Pin7: FAILB
FAIL signal output pin (open drain). As abnormal, the internal NMOS turn on.
Status
Normal
Abnormal
FAILB output
OPEN
GND Level
○Pin8: ADIM
The input output pin for analog dimming signal. The pin function can be changed according to the input level of ADIM_P
pin. The pulse-DC transform circuit is included into BD9285F.
ADIM_P input level
-0.3V<ADIM_P<3.8V
4.2V <ADIM_P<5.6V
ADIM_P pin function
Pulse signal input for
analog dimming
ADIM_P pin function is
masked.
ADIM pin function
DC output signal for
analog dimming
DC input signal for
analog dimming
Required signal to IC
DUTY signal for analog
dimming
DC signal for analog
dimming
Analog dimming
pulse signal
1.4V/1.5V
ADIM_P
3.3V
3.3V
200k
C1
ADIM
Analog dimming
DC signal
R1=10kohm
0.2V
LED current
signal
ISENSE
0% 6%
Figure 12. Analog dimming function and character
DUTY of
ADIM_P [%]
100%
Above functions enable BD9285 use both of the duty and DC signal for analog dimming.
○When the duty signal is used, that input to the pin ADIM_P with the amplitude about
3.3V. The input duty of ADIM_P needs to be larger than 6% so that the output ADIM is
larger than 0.2V. In the case of the normal feedback with analog dimming, The ADIM pin
voltage is equal to the ISENSE pin voltage. Therefore, please be careful that the lower
ADIM voltage than 0.1V causes the OPEN abnormal detection.
○When the DC signal is used, ADIM_P will be pulled up, and the signal input to the pin
ADIM.
In the driver module with more than two BD9285, and the analog dimming is performed
by the duty signal, the architecture will be shown in the right figure. That can reduce the
LED current error between the channels, because the common circuit of the pulse DC
transform is used.
The pulse DC transform circuit outputs DC signal to the ADIM pin with the time constant
of R1, C1 in the above diagram. More C1 value, the ripple components of the ADIM pin
ADIM
PULSE
ADIM
DC
BD9285
ADIM_P
ADIM
BD9285
ADIM_P
ADIM
Figure 13. the analog dimming
circuit as two BD9285 are
used.
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TSZ22111・15・001
10/36
TSZ02201-0F1F0C100030-1-2
11.Jul.2012 Rev.001