BD94121F Datasheet, PDF (13/28 Pages) Rohm – PFC Direct current resonance type White LED Driver for Large LCD

BD9412F
PIN.9 CP
This pin sets up the time from the point of abnormal detection till shut down (Timer Latch). Having 1µA constant
current charges at external capacitor connected to CP pin, it will shut down when it becomes over 2.0V. During soft
start, there is no charge to CP external capacitor even fulfilling CP pin charge condition (timer latch). External
capacitor is set around 0.01µF to 2.2µF).
T_CP
C_CP

V_CP
I_CP

C_CP  2.0
1.0 10^6
 2.0 10⁶  C_CP
[sec]
1uA
Timer Latch Time TCP
100
CCP
10
Timer latch
Shut-down
1
2.0V
0.1
Timer Start
0.01
Figure. 19 CP Block Diagram
0.001
0.001
0.01
0.1
1
10
CP Capacitance CCP[µF]
Figure. 20 Timer Latch Time vs CP Capacitance
PIN.10 PWMIN
By inputting PWM pulse signal at PWMIN pin, it is possible to adjust burst brightness. (High level: over 1.8V, Low
level: below 0.8V).
condition
PWMIN : 1.8V to 5.0V
PWMIN : -0.3V to 0.8V
LED condition
Turn On
Turn Off
PIN.11 ADIM
ADIM pin is Input and Output Pin of DC signal for analog dimming. According to ADIM Input level, each pin’s
function is changed as the followings. Pulse-DC translation Circuit is shown in Figure.20.
PWM2DCinput level
-0.3V<PWM2DC<6.5V
8.5V<PWM2DC<20V
PWM2DC function
Pulse Signal Input
for Analog Dimming
Mask PWM2DC’s
Function
ADIM function
DC Signal Output
for Analog Dimming
DC Signal Input
for Analog Dimming
Needed Signal
from External
DUTY Signal
for Analog Dimming
DC Signal Output
for Analog Dimming
The voltage that ADIM voltage multiplies by (1/4.4) becomes IS threshold voltage and it has linear characteristic.
But, ADIM voltage becomes under 0.44V(Typ), IS threshold voltage is clamped at 0.44V/0.44=0.1V(Typ). And
ADIM voltage becomes over 2.2V(Typ), IS threshold voltage is clamped at 2.2V/0.44=0.5V(Typ). When you want
to use linear characteristic range, please set ADIM voltage from 0.5V to 2.1V.
And pulse signal inputs to PWM2DC terminal and IC can average it by IC internal 100kΩ and the capacitor
connected to ADIM terminal (This means pulse to DC signal transfer circuit.). At this time, ADIM ripple level is
changed by ADIM’s capacitance, therefore please set suitable capacitance according to set specification.
IS
1.0V
0.5V
IS High Det
PWM2DC
Pulse
signal
8.0V/7.0V
0.25V
Gain=1/4.4
0.1V
0.05V
IS Low Det
0.44V
2.2V
ADIM
Figure. 21 IS threshold voltage vs ADIM voltage
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TSZ22111 • 15 • 001
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ADIM
CADIM
2.2V
RADIM
100k
Figure. 22 Pulse to DC transfer block diagram
TSZ02201-0F5F0C100100-1-2
22.Feb.2016 Rev.001