UCC3973PWTRG4 datasheet(10/24 Pages) TI1

Teilenummer	UCC3973PWTRG4

Bauteilbeschribung	BiCMOS Cold Cathode Fluorescent Lamp Driver Controller

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Hersteller	TI1 [Texas Instruments]

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10

UCC1972/3

UCC2972/3

UCC3972/3

Dimming Techniques

Analog Dimming:

A control circuit that implements analog dimming with a

potentiometer (RADJ) is shown in Fig. 2. When the sec-

ondary has a positive polarity current, D1 is reversed bi-

ased and lamp current is sensed directly through RL and

RADJ. When the current reverses direction, D1 conducts

and the voltage on the sense node VX is clamped to the

forward drop of the diode. The resulting waveform at VX

is a half wave rectified sinusoid whose voltage is propor-

tional to lamp current.

()

I

V

RR

LAMP

D

LADJ

=

+

é

ëê

ù

ûú

+

15

2

.

p

(12)

This voltage is averaged by the feedback components

(RFB,CFB) and held to 1.5V by the error amplifier when

the control loop is active. The resulting voltage at the out-

put of the error amplifier (COMP) sets the duty cycle of

PWM stage. Average lamp current is controlled by ad-

justing RADJ to the appropriate value. Resistor RL sets

the high current level of the lamp.

Analog Dimming by PWM or D/A Control Signal:

Analog dimming control of the lamp can be achieved by

providing a digital pulse stream (or DC control voltage)

from the system microprocessor as shown in Fig. 3. For

this technique, the lamp current sense resistor (R1) is

fixed and the VX node voltage is averaged against the

digital pulse stream of the microprocessor. The averag-

ing circuit consists of R2, R3, and CFB. A higher average

value from the pulse stream will result in less average

lamp current. The frequency of the digital pulse stream

should be high enough to maintain a constant DC value

across the feedback capacitor. If a D/A converter is avail-

able in the system, a DC output can be used in place of

the pulse stream.

Low Frequency Dimming (LFD):

Analog dimming techniques described previously can

provide excellent dimming over a 10:1 range, depending

upon the physical layout and the amount of stray capaci-

tance in the backlight's secondary circuitry. Beyond this

level the lamp may begin to exhibit the "thermometer ef-

fect" causing uneven illumination across the tube.

Low frequency dimming (LFD) is accomplished by oper-

ating the lamp at rated current and gating the lamp on

and off at a low frequency. Since the lamp is operated at

full intensity when on, the system layout has little effect

on dimming performance. The average lamp intensity is

a function of the duty cycle and period of the gating sig-

nal. The duty cycle can be controlled to a low minimum

value, allowing a very wide dimming range. Low fre-

quency dimming can be implemented by summing a

PWM signal into the feedback node to turn the lamp off

as shown in Fig. 4. A 68k

W resistor is used for RFB and

RLFD,CFB is reduced to 6.8nF to speed up the lamp

re-strike. The repetition rate of the signal should be

greater than 120Hz to avoid visible flicker.

APPLICATION INFORMATION (cont.)

1.5V

R

FB

C

FB

CBALLAST

R

L

R

ADJ

0V

V

X

V

X

D1

+

–

COMP

FB

Figure 2. Analog dimmer with potentiometer.

C

BALLAST

R1

SECONDARY

D1

1.5V

FB

C

FB

0V

V

X

R3

Dim

Bright

R2

COMP

OR USE DC

CONTROL VOLTAGE

FROM D/A

DIGITAL

PULSE

STREAM

+

–

Figure 3. Analog dimming control from micro- processor.

C

BALLAST

R1

SECONDARY

D1

1.5V

FB

C

FB

0V

V

X

RLFD

RFB

COMP

DLFD

ON

OFF

ON

OFF

LFD CONTROL

SIGNAL

Figure 4. Low frequency dimming by forcing lamp

current off through the FB pin.

Ähnliche Beschreibung - UCC3973PWTRG4

Hersteller	Teilenummer	Datenblatt	Bauteilbeschribung
Texas Instruments	UCC1972	308Kb / 17P	[Old version datasheet] BiCMOS Cold Cathode Fluorescent Lamp Driver Controller
Texas Instruments	UCC1972	895Kb / 24P	[Old version datasheet] BiCMOS Cold Cathode Fluorescent Lamp Driver Controller
Monolithic Power System...	MP1010B	35Kb / 1P	Cold Cathode Fluorescent Lamp Driver
Monolithic Power System...	MP1011A	128Kb / 6P	Cold Cathode Fluorescent Lamp Driver
Texas Instruments	UCC2974	229Kb / 14P	[Old version datasheet] DUAL COLD CATHODE FLUORESCENT LAMP CONTROLLER
Texas Instruments	UCC3974	210Kb / 12P	[Old version datasheet] DUAL COLD CATHODE FLUORESCENT LAMP CONTROLLER
Dallas Semiconductor	DS3984	790Kb / 24P	4-Channel Cold-Cathode Fluorescent Lamp Controller
Maxim Integrated Produc...	DS3988	778Kb / 23P	8-Channel Cold-Cathode Fluorescent Lamp Controller Rev 0; 4/05
	DS3984	508Kb / 24P	4-Channel Cold-Cathode Fluorescent Lamp Controller Rev 1; 5/07
	DS3994	537Kb / 28P	4-Channel Cold-Cathode Fluorescent Lamp Controller Rev 0; 10/06

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