UCC3973PWTRG4 datasheet(9/24 Pages) TI1

Teilenummer	UCC3973PWTRG4

Bauteilbeschribung	BiCMOS Cold Cathode Fluorescent Lamp Driver Controller

Download	24 Pages

Scroll/Zoom	100%

Hersteller	TI1 [Texas Instruments]

Direct Link	http://www.ti.com

Logo

9 / 24 page

9

UCC1972/3

UCC2972/3

UCC3972/3

The current sense resistor RS provides direct control of

lamp current. Since the current sense resistor voltage is

controlled to a 1.5V reference, its power loss is inversely

proportional to its value at a given lamp current.

Synchronizing the Stages

An internal comparator at the BUCK node is used to syn-

chronize the PWM buck frequency to twice the resonant

tank frequency. Synchronization is accomplished with

sync pulse that is generated each time the BUCK node

voltage is within 1.0V of VBAT; the UCC3972/3 uses this

sync pulse to reset the PWM oscillator’s saw-tooth ramp.

The syn circuit will operate at 2 X the transform switching

frequency.

Buck Stage Design

The PWM output controls current in the buck inductor.

The UCC3972/3’s buck power stage differs from a tradi-

tional buck topology in a few respects:

• The topology is inverted using a ground referenced

N-Channel MOSFET rather than a VDD referenced

P-Channel.

• The output voltage is a full wave rectified sinewave at

the switching frequency, rather than DC.

Referring back to Fig. 1, when OUT turns SBUCK on, the

BUCK node voltage VBUCK is placed across the inductor.

This voltage is typically positive and current ramps up in

the inductor (it is possible for the BUCK node voltage to

go negative if VBAT is low and the lamp current is near

maximum).

When

SBUCK

is

turned

off,

VBAT-VBUCK+VDBUCK is placed across the inductor with

opposite polarity. As with any buck converter, the

volt-seconds across the inductor must be reversed on

each switching cycle to maintain constant current. The

duty cycle (D) relationship is complicated somewhat by

the fact the output voltage is changing within a switching

cycle. The equations below determine the relationship

between on and off times in continuous conduction mode

where T is the switching period, D = tON/T, and tOFF =T-

tON.

()

V

dt

VBAT V

V

dt

BUCK

t

BUCK

D

t

T

ON

·=

-

+

·

òò

0

(8)

Selecting the buck inductor:

Maximum ripple current in the inductor occurs when fre-

quency and duty cycle are at a minimum, which corre-

sponds to VBAT and lamp current being a maximum.

The average value of VBUCK at rated lamp current is

equal to:

VV

V

N

VV

V

BUCK AVE

BAT

SEC

BAT

_

.

=-

·

=-

·

=-

·

2

820

2

67

55

p

olts

(9)

The approximate on time using the maximum 22V input

voltage (VBUCK_AVE = 16.4), a 100kHz switching fre-

quency (two times the resonant frequency), and ignoring

the diode drop can be calculated from the following:

t

Tt

VBAT V

V

ON

BUCK AVE

-

=

-

_

(10)

The resulting on time is 2.5

ms. A 150mH inductor will re-

sult in a peak to peak ripple current of 280mA. Average

inductor current (with maximum lamp current) can be cal-

culated by taking the lamp power divided by the tank effi-

ciency and the RMS buck voltage.

I

VI

Efficiency

N

V

BUCK

LAMP

SEC

=

·

æ

è

çç

ö

ø

÷÷· ·

æ

è

çç

ö

ø

÷

2

÷ =

·· ·

·

=

375 0 005 2 67

0 8 820

380

.

mA

(11)

The resulting inductor ripple is less than 50%. A list of

possible inductors are given below along with ESR and

current rating (losses in the inductor are calculated with

RMS current).

The choice of a MOSFET for the buck switch should take

into consideration conduction and switching losses. The

RDS(on) and gate charge are typically at odds, however,

where minimizing one will typically result in the other in-

creasing. An International Rectifier IRFL014 was se-

lected (SOT-223 package) in this application with a gate

charge of 11nC and RDS(on) of 0.2W. A Schottky diode

should be used for the buck diode in order to minimize

forward drop.

APPLICATION INFORMATION (cont.)

Vendor

L

Part Number

ESR

Current

Rating

Coilcraft

(847) 639-6400

150

mH DO3316-154 0.38

1A

Coiltronics (407)

241-7876

150

mH

CTX150-4

0.175

0.72A

Sumida

(847) 956-0666

150

mH CDR125-151

0.4

0.85A

Toko (847) 297-0070 150

mH 646CY-151

0.73

0.4A

Table 3. Inductor Suppliers

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

More results

UCC3973PWTRG4 Datenblatt(PDF) 9 Page - Texas Instruments

UCC3973PWTRG4 Datenblatt(HTML) 9 Page - Texas Instruments

Ähnliche Teilenummer - UCC3973PWTRG4

Ähnliche Beschreibung - UCC3973PWTRG4

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datenblatt Download

Link URL