BD92111F Datasheet, PDF (11/28 Pages) Rohm – PFC Direct current resonance type White LED Driver for Large LCD

BD92111F
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.
BD92111F
OSC
Error Amp
Figure. 14 RRT and RADJ Resistor connection method
RT
RADJ
RRT
FB IS
CFBIS
CFBVS
VS
RFBIS
RFBVS
Figure. xx
As shown by left graph, by changing resistor RADJ
between FB and RT, it is possible to determine the
modulation width of frequency.
Modulation width of frequency determined by the
resistor between FB and RT resistor (Theoretical
formula : Example)
When RADJ=100kΩ , Δ fOUT=84.46kHz
.
Figure. 15 Modulation width of Output Frequency vs RADJ Resistance
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=84.46kHz
FB voltage Vin [V]
Figure. 16 Output Frequency vs FB Voltage
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.
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TSZ22111 • 15 • 001
11/24
TSZ02201-0F5F0C100090-1-2
31.Jan.2016 Rev.001