UCC2974 Datasheet, PDF (7/14 Pages) Texas Instruments – DUAL COLD CATHODE FLUORESCENT LAMP CONTROLLER

VIN
T1
UCC2974
UCC3974
ą
SLUS485A – JULY 2001 – REVISED NOVEMBER 2001
VIN
T2
R2
750Ω
C3
Q2
C8
R6
750Ω
Q3
C2
Q1
33 pF
3 kV
VIN
D2
VIN
100µF
35 V
Q4
VIN
L2
D3
100µH
Q5
100µF
35 V
UCC3974
1 OUT1 OUT2 16
R9
10Ω
100µF
35 V
Q6
R10
10 Ω
2 VIN
GND 15
3 OUT1 OUT2 14
R3
C4
C8 1µF
4 COMP1 CBP 13
C7
R5
5 FB1 COMP2 12
R1
D1 ^{750 Ω}
R8 200 kΩ
C5
6 RT1
FB2 11
10 nF
R4 20 kΩ
R11
7 RT2 MODE 10
10 kΩ
C6
BRIGHT
8 DIM LFDSYNC 9
1 µF
SYNC
Figure 1. Typical Dual-Channel Application
C9
33 pF
3 kV
R7
750 _{Ω D4}
R12
10 kΩ
UDG–01020
low-frequency dimming (LFD)
The low-frequency dimming section of the device is implemented as either a low frequency pulse width
modulator (PWM) or as a direct digital input. In either case, the DIM pin is the controlling input. The type of DIM
input is determined at startup. As the MODE pin transitions through the LFD_ENABLE threshold, the LFDSYNC
pin is observed. When this pin is high, the DIM pin is a 2.5-V compatible logic input. When the DIM pin is high,
the output is enabled. When it is low the output is disabled. The user is required to provide the correct frequency
and duty ratio to the DIM pin in this mode. To change the mode of operation without power cycling the device,
the MODE pin must be brought below the LFD_ENABLE threshold and then brought above it with the LFDSYNC
pin held in the desired state.
To use DIM as an analog input, the LFDSYNC pin must be low when mode crosses the LFD_ENABLE threshold.
In this mode, DIM becomes an analog input that varies the amount of time that the lamp is on during the period
of the LFD oscillator. From 0.5 V to 3 V applied to the DIM pin varies the lamp on duty cycle from the programmed
minimum to 100%.
NOTE: The analog dimming signal is senitive to coupled noise from the lamps. Noise on this line
will be seen as lamp flicker. It is highly reccommended that precautions be taken to prevent noise
coupling to this signal for optimum results.
Applying a pulse train to the LFDSYNC pin will synchronize the LFD oscillator to that pulse train. The frequency
of the applied pulse train must be higher than the free running frequency of the oscillator.
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