MAX11504/MAX11505
Four-Channel, Standard-Definition
Video Filters
8 _______________________________________________________________________________________
Applications Information
Output Configuration
The MAX11504/MAX11505 outputs may be either DC-
or AC-coupled. If AC-coupled, choose a capacitor that
passes the lowest frequency content of the video signal,
and keep the line-time distortion within desired limits. The
capacitor value is a function of the input leakage and
impedance of the circuit being driven. Common industry
practice is to use a 220µF or larger coupling capacitor. If
any or all outputs are driving two parallel loads, see the
Junction Temperature Calculations
section.
The MAX11504/MAX11505 outputs are fully protected
against short circuits either to the ground or the positive
supply of the device. The short-circuit protection cir-
cuitry limits the output current to 80mA (typical) per out-
put. Shorting more than one output simultaneously can
exceed the maximum package power dissipation.
Junction Temperature Calculations
Die temperature is a function of quiescent power dissi-
pation and the power dissipation in the output drivers.
Calculate the power dissipated P
D
using:
where P
DS
is the quiescent power dissipated in the die,
and given by:
and where P
DOn
is the power dissipated in the n
th
dri-
ver stage and given by:
where V
ORMSn
is the RMS output voltage and R
L
is the
load resistance.
Example - Assuming these conditions:
1) Video standard = 525/60/2:1.
2) Video format = RGB with syncs on all channels.
3) Picture content = 100% white.
4) The input signal is AC-coupled.
5) The output signal is DC-coupled.
6) V
CC
= 5.0V.
7) I
CC
= 24mA.
A sync tip exists at 280mV and peak white exists at
2.28V. The RMS voltage will be approximately 1.88V on
each output (80% of the peak-peak voltage, plus the
offset) giving:
and
The junction temperature is given by:
where T
J
= junction temperature, T
A
= ambient temper-
ature (assume +70°C) and R
θJA
= thermal resistance
junction to ambient.
From the
Absolute Maximum Ratings
section of the
data sheet, the derating factor is 8.8mW/°C above
+70°C. R
θJA
= 1/(derating factor) = 1/(8.8mW/°C) =
113°C/W.
Therefore:
If there is only one video load on each output, the junc-
tion temperature lowers to:
The above calculations assume the use of a multilay-
ered board with extensive ground planes for high ther-
mal efficiency. Using such a board is especially
important in applications where there are two video
loads on each channel.
(.).
.
