FAN7310 Datasheet, PDF (7/12 Pages) Fairchild Semiconductor – LCD Back Light Inverter Drive IC

FAN7310
Function Description
UVLO : The under voltage lockout circuit guarantees
stable operation of the IC’s control circuit by stopping
and starting it as a function of the Vin value. The UVLO
circuit turns on the control circuit when Vin exceeds 5V.
When Vin is lower than 5V, the IC’s standby current is
less than 200uA.
ENA : Applying the voltage higer than 2V to ENA pin
enables the operation of the IC. Applying to the voltage
lower than 0.7V to ENA pin will disable the operation of
the inverter.
Soft start :The soft start function is provided that S_S
pin is connected through a capacitor to GND. A soft
start circuit ensures a gradual increase in the input and
output power. The capacitor connected to S_S pin
determines the rate of rise of the duty ratio. It is
charged by a current source of 6uA.
Burst oscillator & burst dimming :Timing capacitor
BCT are charged by the reference current source,
formed by the timing resistor Rt whose voltage is regu-
lated at 1.25V. The sawtooth waveform charges up to
2V. Once reached, capacitors begin discharging down
to 0.5V. Next timing capacitors start charging again and
a new switching cycle begins. The burst dimming fre-
quency can be programmed with adjusting the values
of Rt and BCT. The burst dimming frequency can be
calculated as below.
Main oscillator : Timing capacitor CT are charged by
the reference current source, formed by the timing
resistor Rt whose voltage is regulated at 1.25V. The
sawtooth waveform charges up to 2V. Once reached,
capacitors begin discharging down to 0.5V. Next timing
capacitors start charging again and a new switching
cycle begins. The main frequency can be programmed
with adjusting the values of Rt and CT. The main fre-
quency can be calculated as below.
fburst
=
-------------3---.--7---5-------------
64 RT BCT
The burst dimming frequency should be greater than
120Hz to avoid visible flicker.
To compare the input of BDIM pin with the 0.5~2V trian-
gular wave of burst oscillator makes the PWM pulse for
burst dimming. The PWM pulse controls EA_OUT’s
voltage by summing 85uA into EA_IN pin.
fop
=
-------------1---9--------------
32 RT CT
7