FMS6408MTC143XNL Fairchild Semiconductor, FMS6408MTC143XNL Datasheet - Page 9

• Manufacturer Part Number: FMS6408MTC143XNL
• Manufacturer: Fairchild Semiconductor

Specifications of FMS6408MTC143XNL

• Lead Free Status / RoHS Status: Compliant

© 2004 Fairchild Semiconductor Corporation
FMS6408 Rev. 3.0.0
Application Notes
Introduction
The FMS6408 can drive dual 75Ω loads, where each
load consists of a 75Ω resistor in series with a 75Ω
termination resistor in the driven device. This
presents a 150Ω load to the output, so two similar
loads in parallel look like 75Ω from the output to
ground. In some cases, it may be desirable to drive a
single load on one or more outputs with a dual load
on the remaining outputs. This is an acceptable
loading condition, but can cause a slight degradation
in gain matching.
Device Power Dissipation
The FMS6408 specifications provide a quiescent no-
load supply current of 52mA (typical). With a nominal
5V supply, this results in a power dissipation of
260mW. The overall power dissipation can be
significantly affected by the applied load, particularly
in DC-coupled applications. To calculate the total
power dissipation the typical output voltages and the
loading must be known.
The highest power dissipation occurs for YUV video
signals DC-coupled into dual video loads (refer to
Figure 3).
Assume a video signal on the Y channel that
averages 50% luminance with an output voltage of
1.55V, then calculate the load current:
The device dissipation due to this load is the
internal voltage drop multiplied by the load current:
I
P
LOAD
D
(
Y
)
(
Y
=
)
5 (
=
V
. 1
−
55
. 1
V
55
Figure 12.
/
V
75
)
+5V
Ω
•
V
20
+ VI
CC
+ V
+ VI
=
I
I
I V
Driver
U
Driver
Driver
Y
6 .
I
U
20
Y -
V
-
-
mA
6 .
YUV Video Signals that are DC-Coupled into Dual Video Loads
mA
U
Y OUT
V
OUT
OUT
=
71
mW
1.825V
1.125V
0.425V
1.825V
1.125V
0.425V
1.825 V
2.25V
1.55V
0.85V
0.25V
(1)
(2)
9
The average DC level for the U and V channels is set
by the clamp circuit to 1.125V. The signal is
symmetrical about this voltage, therefore:
The device dissipation due to this load is the internal
voltage drop multiplied by the load current:
Since the U and the V power dissipation are
approximately the same, the total dissipation due to
load can be estimated by:
This
dissipation
187.55mW (load power) or 447.55mW. It is
advisable to calculate the highest possible power
dissipation using worst-case quiescent supply
current and the maximum allowable power supply
voltage.
calculating the die temperature rise with the
supplied θ
Field Time Distortion
In applications with AC-coupled outputs, the AC-
coupling capacitors dominate the field time distortion.
Performance is specified with 220µF coupling
capacitors; if better performance is desired, the
capacitors may be increased or the outputs may be
DC-coupled.
P
I
P
71
LOAD
D
D
75Ω
75Ω
75Ω
75Ω
75Ω
75Ω
mW
(
(
) U
Ω
load
(
=
brings
) U
+
5 (
)
75Ω Video Cables
2
=
=
This
JA
V
•
( P
. 1
, thermal resistance value.
58
−
to
125
Y
. 1
the
.
)
125
125
result
+
260mW
V
2
mW
/
V
•
typical
75
)
( P
•
75Ω
75Ω
75Ω
75Ω
75Ω
75Ω
Ω
15
) U
should
=
=
187
mA
=
(quiescent
15
total
mA
.
=
55
58
be used when
mW
.
device
125
www.fairchildsemi.com
mW
power)
power
(3)
(4)
(5)
+