FMS6143A Datasheet, PDF (10/13 Pages) Fairchild Semiconductor – Low-Cost Three-Channel 6th-Order Standard Definition 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 16. 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 17. DC-Coupled Inputs, AC-Coupled Outputs
DVD or
STB
SoC
DAC
Output
0V - 1.4V
0.1μ
LCVF
Clamp
Active
75Ω ^220μ
Figure 18. AC-Coupled Inputs and Outputs
External video
source must
be AC coupled
0V - 1.4V
0.1μ
75Ω
LCVF
Clamp
Active
75Ω ^220μ
Figure 19. Biased SCART with AC-Coupled Outputs
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 FMS6143A 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 and
(2)
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 = 15mA
VCC = 3.3V
RL = channel load resistance.
Board layout can also affect thermal characteristics.
Refer to the Layout Considerations section for details.
The FMS6143A 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.
© 2009 Fairchild Semiconductor Corporation
FMS6143A • Rev. 1.0.0
10
www.fairchildsemi.com