BD94121F Datasheet, PDF (10/28 Pages) Rohm – PFC Direct current resonance type White LED Driver for Large LCD

BD9412F
Pin Function Description
PIN.1 VCC
This is power supply pin for the IC. Normal operation range (Typ) is from 9V to 18V. Please place ceramic
capacitor bigger than 0.1µF as bypass capacitor between VCC and GND. It is for noise elimination.
PIN.2 STB
This PIN is for setting of ON/OFF. It is possible to use as reset when shutting down.
Please set the STB terminal voltage below VCC voltage. In addition, please set below 4V if the voltage is applied
earlier than VCC.
Depending on input voltage to STB pin, the status of IC might be switched (ON/OFF). Please avoid using between
the two status (0.8V to 2.0V)
PIN.3 GND
This is signal system GND for IC inside. Please make it independent from PGND as much as possible (We
recommend this because it has less influence with switching noise which comes from short circuit of PGND and
GND at connector close to GND pin.
Vin
GND_PIN
PGND
N1
N2
GND
Figure. 11
PIN.4 RT
Set up the charge/discharge current by frequency of IC inside.
By changing the resistance value of resistor between RT pin and GND, it is possible to set up basic drive
frequency as following formula;
Basic frequency means output N1, N2 frequency which is determined only with resistor between RT pin and GND.
f_OUT
6000 _[kHz]
R_RT [k]
6673
f_OUT _{RRT [k]  3.336} [kHz]
( f_OUT 200 kHz)
( f_OUT  200 kHz)
1,000
BD94121F
OSC
Error Amp
100
RT
FB
IS
VS
CFBIS
RFBIS
10
CFBVS
RFBVS
RRT
1
10
100
RT Resistance : RRT [kΩ]
1,000
Figure. 12 RT Resistance vs Output Frequency
Figure. 13 RRT Resistor connection method
There is a discrepancy between theoretical formula and actual device. For frequency setting, please thoroughly
verify it with actual application. In addition, frequency may change upon resistor RADJ which is placed between
RT and FB pins
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TSZ22111 • 15 • 001
10/24
TSZ02201-0F5F0C100100-1-2
22.Feb.2016 Rev.001