BD94121F Datasheet, PDF (11/28 Pages) Rohm – PFC Direct current resonance type White LED Driver for Large LCD

BD9412F
PIN.5 FB
This is output pin for LED current feedback (IS pin) error amplifier and open LED voltage feedback (VS pin) error
amplifier. The capacitance between FB and IS (1500pF to 0.01µF) also determines start up time of LED current
necessary during phase compensation and brightness adjustment. Capacitance between FB and VS (1500pF to
0.01µF) is for phase compensation of error amplifier.
BD94121F
OSC
Error Amp
Figure. 14 RRT and RADJ Resistor connection method
RT
RADJ
RRT
FB IS
CFBIS
CFBVS
VS
RFBIS
RFBVS
Moduration width of Output Frequency
150
125
As shown by left graph, by changing resistor RADJ
108.1
between FB and RT, it is possible to determine the
modulation width of frequency.
100
Modulation width of frequency determined by the
75
resistor between FB and RT resistor (Theoretical
formula : Example)
When RADJ=100kΩ , Δ fOUT=108.1kHz
50
25
Figure. xx
0
10
100
1000
Figure. 13 出力周波数^R変^AD動^{J Re}幅^sistan対^{ce : R}R^ADA^J D^[kJ^Ω]抵抗値 特性
Figure. 15 Modulation width of Output Frequency vs RADJ Resistance
Output Frequency vs FB Voltage
200
180
167.8
160
140
120
100
80
60
59.7
40
20 _0.5
3.2
0
0
1
2
3
4
5
6
FB Voltage : VFB [V]
Figure. 16 Output Frequency vs FB Voltage
Modulation width of frequency determined by the
resistor between FB and RT resistor (Theoretical
formula : Example)
When RADJ=100kΩ , Δ fOUT=108.1kHz
The basic drive frequency is determined by resistor RRT which is connected from RT pin to GND. The basic
frequency is the one at VFB=1.5V, and operation frequency range will be fixed with frequency modulation width that
is determined by RADJ under this condition. When RRT=51kΩ, fOUT=127.7kHz becomes to basic drive frequency.
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TSZ22111 • 15 • 001
11/24
TSZ02201-0F5F0C100100-1-2
22.Feb.2016 Rev.001