FMS6143_08 Datasheet, PDF (8/11 Pages) Fairchild Semiconductor – Low-Cost Three-Channel 4th-Order Standard Defi nition 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
be AC coupled
0V - 1.4V
0.1μ
75Ω
LCVF
Clamp
Active
75Ω ^220μ
External video
source must
7.5MΩ
be AC coupled ^0.1μ
LCVF
75Ω
Bias
Input
Figure 17. Biased SCART with
AC-Coupled Outputs
75Ω
500mV +/-350mV
NOTE: The video tilt or line time distortion is dominated by
the AC-coupling capacitor. The value may need to be incre-
ased beyond 220μF to obtain satisfactory operation in
some applications.
Figure 14. 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 15. DC-Coupled Inputs,
AC-Coupled Outputs
DVD or
STB
SoC
DAC
Output
0V - 1.4V
0.1μ
LCVF
Clamp
Active
75Ω ^220μ
Figure 16. AC-Coupled Inputs and Outputs
Power Dissipation
The FMS6143 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.
T_J = T_A + P_d • θ_JA
(1)
where: P_d = P_CH1 + P_CH2 + P_CH3 and
(2)
P_CHx = V_CC • I_CH - (V_O²/R_L)
(3)
where: V_O = 2V_IN + 0.280V
(4)
I_CH = (I_CC/3) + (V_O/R_L)
(5)
V_IN = RMS value of input signal
I_CC = 19mA
V_CC = 5V
R_L = channel load resistance
Board layout can also affect thermal characteristics. Refer
to the Layout Considerations section for details.
The FMS6143 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.
© 2006 Fairchild Semiconductor Corporation
FMS6143 Rev. 4.0.7
8
www.fairchildsemi.com