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Short to Battery Protection Circutiry for Automotive Video Decoder

Question asked by Rob.Analog on Oct 31, 2014
Latest reply on Nov 3, 2014 by harryh

Dear Sir/Madam,


One of my customers is using an ADI video decoder (ADV7280) in an automotive environment. They are feeding analog video over a CVBS cable into the ADV7280.

Our recommended input circuit to the ADV7280 uses a resistor divider (24 Ohm and 51 Ohm) and an 100nF AC coupling capacitor. Please see the attached input network circuit.

 

The customer also requires that the analog video input network needs to be robust to 24V short to battery events (STB) i.e. car battery accidentally getting shorted onto the analog video input line.

 

The AC coupling capacitor will protect the ADV7280, however the 24 Ohm and 51 Ohm resistors could be damaged during the STB event.

We cannot move the location of the AC coupling capacitor or insert additional DC blocking capacitors without upsetting the operation of the video decoder.


I was hoping that some of the voltage protection devices designed for power supply applications could be used to protect the 24 Ohm and 51 Ohm input network resistors during STB events. I was particularly wondering if I could just place an ADG465 in series to protect the resistors. 

http://www.analog.com/static/imported-files/data_sheets/ADG465.pdf

 

I would appreciate any feedback anyone could give on whether this is a valid solution. Once I have a solution I will add this as a recommended solution to all our video decoder customers.

 

FYI analog CVBS video signals are generally 1V peak to peak. The DC level can vary from (bottom of CVBS signal at) 0V up to (top of CVBS signal at) 1.8V .

 

Regards,

Robert Hinchy,

Senior Applications Engineer,

Digital Video Products Group,

Analog Devices Inc,

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