MP1048 – FULL BRIDGE CCFL CONTROLLER
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.
For DMIN=0.1 and R6=212kꢀ
1− DMIN
C7 =
fb × R6 × γ
For DMIN=0.1, R6=212k, fb=200Hz, then
C7=52nf:
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.
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.
IMPORTANT–For all applications, VCCR and
VCCL must be connected together.
3.6
2.4
⎛
⎞
⎟
γ = ln
≈ 0.405
⎜
⎝
⎠
Pin 11 (DBRT):
ESD Resistor
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.
It is recommended that a resistor (RLI = 1kꢀ) 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.
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:
MP1048
LI
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.
Figure 4—ESD Resistor
These values are determined as follows:
Select a Minimum Duty Cycle, DMIN, where:
DMIN = tMIN × fBurst
tFALL
DMIN
=
(
tFALL + tRISE
)
If operating in Free-Running mode:
⎛
⎞
⎟
⎠
1
⎜
⎜
⎟
− 1 Vbg
DMIN
VP + VV
⎝
+
ξ
2
R6 =
Ib
⎛
⎞
1
⎜
⎜
⎟
R6 ~ 21.16k
− 1 + 21.43k
⎟
DMIN
⎝
⎠
MP1048 Rev. 0.9
9/24/2007
www.MonolithicPower.com
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10
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