Four-Channel, Standard-Definition

Video Filter

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 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.

and given by:

ver stage and given by:

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

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:

junction to ambient.

From the

Absolute Maximum Ratings section of the

data sheet, the derating factor is 8.8mW/°C above

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.

TC

°

101

TC

×

= +

°

70 113

0 432

119

.

TT

R

P

J

A

JA

D

=+

×

()

θ

PW

++++=

0 12 0 078 0 078 0 078 0 078 0 432

.

.....

PW

−

×

=

(.

)

.

.

5 1 88

1 88

75

0 078

PW

=

5 0 024

0 12

..

P

VV

V

R

DOn

CC

ORMSn

ORMSn

L

=

−

×

()

PV

I

DS

CC

CC

=×

P

P

P

PPP

D

DS

DO

DODODO

=

+

+++

1

234