MP1026 – CCFL DRIVER FOR HANDHELD DISPLAY APPLICATIONS
Cisb and Risb make up a high-pass filter,
There is no impact on the open lamp time. The
secondary short turn off time is:
wherein the corner frequency should be
between 1KHz and 2KHz so as to minimize the
attenuation of the AC signal.
Cft2 (µF)×1.2V
T(short) =
120µA
The recommended value for Risb is 100kꢀ.
With a smaller capacitor value for Cft2 (when
compared to Cft), the turn off time for the
secondary short will be further reduced.
1
1.6nF =
Cisb >
> Cisb
2π × Risb ×1KHz
1
= 0.8nF
Lamp Startup
2π × Risb × 2KHz
The strike voltage of the lamp will always be
guaranteed at any temperature because the
MP1026 uses a resonant topology for switching
the outputs. The device will continue to switch
at the resonant frequency of the tank until the
strike voltage is achieved. This eliminates the
need for external ramp timing circuits to ensure
startup.
A typical value for Cisb is 1.2nF.
Fault Timer: The timing for the fault timer will
depend on the sourcing current, as described
above, and the capacitor on the FT pin. The
user can program the time for the voltage to
rise before the chip detects a “real” fault. When
a fault is triggered, then the internal drive
voltage (VDrv) will collapse from VDD to 0V.
ESD Resistor
It
is
recommended
that
a
resistor
For open lamp time:
(RIL=470ꢀ~1kꢀ) be added in series with the
Cft (µF)×1.2V
lamp current feedback as shown in Figure 3.
T(open _lamp) =
1µA
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 secondary short turn off time:
Cft (µF)×1.2V
T(short) =
120µA
The off time when a resistive short occurs
across the lamp will be approx 100 times faster
than the open lamp time. To reduce the turn off
time even further, then by modifying the
connection at the FT node to:
MP1026
IL
MP1026_F03
FT
Figure 3—ESD Resistor
C
C
ft2
ft
MP1026_F02
Figure 2—Turn Off Time Adjustment
MP1026 Rev. 1.6
9/24/2007
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