MP1048 – FULL BRIDGE CCFL CONTROLLER
APPLICATION INFORMATION
Pin 1 (SI), R1:
Secondary Short Protection: R1 is used for
feedback to the SI pin to detect excessive
secondary current. The value for R1 is calculated
as 1.2V divided by the secondary peak current.
Pin 2 (LV): C13, C14 and R8:
Open Lamp protection: The regulated open
lamp voltage is proportional to the C14 and C13
ratio. C13 has to be rated at 3kV and is typically
between 5pF to 22pF. The value of C14 is set
by the customer to achieve the required open
lamp voltage detection value.
C14
=
C13
×
1.18
×
V
(
MAX
)
rms
Figure 3—Timeout Adjustment
For a C2B = 10nF, then the time out for
secondary short will be 0.2ms.
Note: The open lamp time out will remain the
same value as defined by C2A.
Pin 7 (LCS), R3:
R3 is used to set the lamp operating clock. The
value for R3 is calculated by
R3
=
5e
9
f
ο
For R3 = 100kΩ, operating clock will be 50KHz.
Pin 8 (LCC):
This is the lamp clock control compensation pin
and needs a lag lead lag capacitor/resistor
network.
Pin 4 (COMP), C1:
C1 is the feedback compensation capacitor that
connects between COMP and AG. A 1.5nF or
2.2nF cap is recommended. This cap should be
X7R ceramic. The value of C1 affects the
soft-on rise time and soft-off fall time.
Pin 18 (OUTR), Pin 25 (OUTL), C12, R9:
The OUTR and OUTL pins are used to sense
the voltage at the output of the full bridge. They
are also the point of access for the output
dampers. OUTR and OUTL should make a
Kelvin connection to the sources of the
high-side MOSFETs and the drains of the
low-side MOSFETs in the output bridge.
The primary transformer current flows through
capacitor C12. Its value is typically 2.2µF. This
capacitor should be ceramic and has a ripple
current rating greater than the primary current.
It is more optimal to use two parallel 1µF
ceramic caps for minimal ESR losses. R9 is
used to ensure that the bridge outputs are at 0V
prior to startup. Typically R9 = 300Ω to 3kΩ.
The value of bias resistor R8 is typically 100kΩ
(not critical).
Pin 2 (LI), R2:
Lamp Current Regulation: R2 is used for
feedback to the LI pin to regulate the lamp
current. The value for R2 is calculated as 1.33V
divided by the lamp rms current (assuming
V
ABRT
is greater than 1.2V). For a RMS 6mA
lamp current, the R2 value is 220Ω.
Pin 6 (FT), C2:
C2 is used to set the fault timer. This capacitor
will determine when the chip will reach the fault
threshold value.
Open Lamp Time Out:
C2
(
nF
)
=
t
OPEN LAMP
×
1
µ
A
1. 2 V
For C2 = 820nF, then the timeout for open lamp
will be 0.98 sec.
Secondary Over Current Timeout: When the
MP1048 is regulating secondary over current
(SI feedback), the source current in the Fault
Timer (FT) cap is approximately 65µA. This
causes the SI timeout to be about 1/65 of the
Open Lamp (LV) timeout. To reduce the SI
timeout further, modify the network at the FT
pin as shown in Figure 3.
FT
C2A
C2B
MP1048 Rev. 0.9
9/24/2007
www.MonolithicPower.com
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© 2007 MPS. All Rights Reserved.
9
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