MAX11504 Datasheet, PDF (8/12 Pages) Maxim Integrated Products – Four-Channel, Standard-Definition Video Filter

Four-Channel, Standard-Definition
Video Filter
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 sig-
nal, and keep the line-time distortion within desired lim-
its. 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, refer to the junction temperature calculations.
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:
P_D = P_DS + P_DO1 + P_DO2 + P_DO3 + P_DO4
where P_DS is the quiescent power dissipated in the die,
and given by:
P_DS = V_CC × I_CC
and where P_DOn is the power dissipated in the n^th dri-
ver stage and given by:
P_DOn
=
(V_CC
−
V_ORMSn ) ×
R_L
V_ORMSn
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:
P_DS = 5 × 0.024 = 0.12W
P_DOn
=
(5 − 1.88) × 1.88
75
= 0.078W
and
P_D = 0.12 + 0.078 + 0.078 + 0.078 + 0.078 = 0.432W
The junction temperature is given by:
T_J = T_A + (R_θJA × P_D)
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:
T_J = 70 + 113 × 0.432 = +119°C
If there is only one video load on each output, the junc-
tion temperature lowers to:
T_J = +101°C
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.
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