FMS6144A Datasheet, PDF (10/13 Pages) Fairchild Semiconductor – Low-Cost, Four-Channel, 6th-Order SD Video Filter Driver

The same method can be used for biased signals, with
the addition of a pull-up resistor to make sure the clamp
never operates. The internal pull-down resistance is
800kΩ ±20%, so the external resistance should be
7.5MΩ to set the DC level to 500mV.
External video
source must
7.5MΩ
be AC coupled ^0.1μ
75Ω
500mV +/-350mV
LCVF
75Ω
Bias
Input
Figure 18. Biased SCART with DC-Coupled Outputs
The same circuits can be used with AC-coupled outputs
if desired.
DVD or
STB
SoC
DAC
Output
0V - 1.4V
0.1μ
LCVF
Clamp
Active
75Ω ^220μ
Figure 19. DC-Coupled Inputs, AC-Coupled Outputs
DVD or
STB
SoC
DAC
Output
0V - 1.4V
0.1μ
LCVF
Clamp
Active
75Ω ^220μ
NOTE: The video tilt or line time distortion is dominated
by the AC-coupling capacitor. The value may need to
be increased beyond 220μF to obtain satisfactory
operation in some applications.
Power Dissipation
The output drive configuration must be considered when
calculating overall power dissipation. Care must be taken
not to exceed the maximum die junction temperature. The
following example can be used to calculate the power
dissipation and internal temperature rise.
TJ = TA + PD • θJA
(1)
where:
PD = PCH1 + PCH2 + PCH3
(2)
and
PCHX = VCC • ICH - (VO2/RL)
(3)
where:
VO = 2VIN + 0.280V
(4)
ICH = (ICC/3) + (VO/RL)
(5)
VIN = RMS value of input signal
ICC = 19mA
VCC = 3.3V.
RL = channel load resistance
Board layout can also affect thermal characteristics.
Refer to the Layout Considerations section for details.
The FMS6144A is specified to operate with output
currents typically less than 50mA, more than sufficient
for a dual (75Ω) video load. Internal amplifiers are
current limited to a maximum of 100mA and should
withstand brief-duration short-circuit conditions. This
capability is not guaranteed.
Figure 20. AC-Coupled Inputs and Outputs
External video
source must
be AC coupled
0V - 1.4V
0.1μ
75Ω
LCVF
Clamp
Active
75Ω ^220μ
Figure 21. Biased SCART with AC-Coupled Outputs
© 2009 Fairchild Semiconductor Corporation
FMS6144A • Rev. 1.0.1
10
www.fairchildsemi.com