MP1048 – FULL BRIDGE CCFL CONTROLLER

MP1048 Rev. 0.9

www.MonolithicPower.com

6

9/24/2007

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2007 MPS. All Rights Reserved.

OPERATION

FAULT

MANAGEMENT

ERROR

AMP

LAMP

CLOCK

VPS

VCCR

R8

RLI

1.2V

R2

C2

C1

R3

R4

R6

C4

R1

1.2V

1

3

6

2

12

4

7

8

10

9

13

11

5

SI

LV

FT

LI

LI

ABRT

COMP

LCS

LCC

BRS

BRC

EN

DBRT

AG

BURST

RATE

GENERATOR

BURST

PWM

LEVEL

SHIFT

LEVEL

SHIFT

C3

R7

C7

C10

C12

R9

VPS

VPS

SI LV

LI

C8

C11

C13

C14

C9

22

24

23

25

27

28

26

15

17

16

18

20

21

19

PRL

UGL

BTL

OUTL

LGL

PGL

VCCL

PRR

UGR

BTR

OUTR

LGR

PGR

VCCR

Figure 1—Functional Block Diagram

DESIGN INFORMATION

The MP1048 is a fixed operating frequency

inverter controller specifically designed to drive

up to 6 cold cathode fluorescent lamps (CCFLs)

used as a backlight for liquid crystal displays.

Designed to run off 10V to 22V input supplies,

the MP1048 can drive up to 6 lamps via four (4)

external N-Channel MOSFETs. Its full bridge

architecture converts unregulated DC input

voltages to the nearly pure sine waves required

to ignite and operate CCFLs. The operating

frequency is set by an external resistor to

minimize the possibility of interference with the

refresh rate of the display.

To ensure ignition of the lamp, the operating

frequency is swept temporarily to the unloaded

resonant frequency of the tank. Regulated lamp

current

and

maximum

peak

transformer

secondary current are set by external resistors.

Regulated open lamp voltage is set by an

external capacitive voltage divider. Soft startup

of the lamp minimizes the peak transformer

secondary voltage. The MP1048 implements

burst mode dimming of the lamp and features

soft-on/soft-off control of the lamp current

envelope that is virtually independent of supply

voltage.

Burst repetition rate and duty cycle can either

be determined by driving the MP1048 with an

external logic signal or by choosing an external

resistor and capacitor to set the burst rate and

modulating the duty cycle with a DC control

voltage on DBRT.

Loop gain is compensated for variations in

supply voltage and the full-wave lamp current

sense amplifier provides superior output pulse

symmetry, loop response time and phase

margin.