MP1048 – FULL BRIDGE CCFL CONTROLLER

MP1048 Rev. 0.9

www.MonolithicPower.com

10

9/24/2007

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© 2007 MPS. All Rights Reserved.

Pin 16 (BTR), Pin 23 (BTL), C8, C10:

BTR and BTL are the bias supplies for the level

shift of the upper MOSFETs. C8 and C10

should be 22nF and made of X7R ceramic

material.

Pin 19 (VCCR), Pin 26 (VCCL), C9, C11:

These capacitors bypass the gate supply for the

low-side switches. They also supply power to

the MP1048. These pins should be bypassed

with a 0.47µF ceramic X7R capacitor.

IMPORTANT–For all applications, VCCR and

VCCL must be connected together.

Pin 11 (DBRT):

This pin is used for burst brightness control.

The DC voltage on this pin will control the burst

percentage on the output. The signal is filtered

for optimal operation. A voltage ranging from 0V

to 1.2V on DBRT will correspond to a Burst

Duty

Cycle

of

the

minimum

to

100%

respectively.

For direct Pulse Width Modulation of the burst

signal, connect BRS to VCC and connect DBRT

with a logic level PWM signal. A logic High is

Burst On and a logic Low is Burst Off.

Pin 10 (BRS): C7, R6:

BRS is used to set the Burst Repetition Rate.

C7 and R6 will set the burst repetition rate and

the minimum burst time: tMIN. Set tMIN to achieve

the minimum required system brightness.

Ensure that tMIN is long enough that the lamp

does not extinguish.

These values are determined as follows:

Select a Minimum Duty Cycle, DMIN, where:

Burst

MIN

MIN

f

t

D

×

=

()

RISE

FALL

FALL

MIN

t

t

t

D

+

=

If operating in Free-Running mode:

b

V

P

MIN

I

2

V

V

Vbg

1

D

1

6

R

+

+

ξ

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

=

k

43

.

21

1

D

1

k

16

.

21

~

6

R

MIN

+

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

For DMIN=0.1 and R6=212kΩ

γ

×

×

−

=

6

R

f

D

1

7

C

b

MIN

For

DMIN=0.1,

R6=212k,

fb=200Hz,

then

C7=52nf:

Where

DMIN=Minimum Burst Duty Cycle,

Vbg=VP - VV (~1.2V), VP=peak BRS voltage

(~3.6V), VV = valley BRS voltage (~2.4V) and

fb=burst repetition rate.

405

.

0

4

.

2

6

.

3

ln

≈

⎟

⎠

⎞

⎜

⎝

⎛

=

γ

ESD Resistor

It is recommended that a resistor (RLI = 1kΩ) be

added in series with the lamp current feedback

as shown in Figure 4.

The addition of this resistor helps minimize the

possibility

of

ESD

damage

in

case

of

mishandling of the IC during board level

assembly and test.

MP1048

LI

Figure 4—ESD Resistor