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Protection Diodes on PGA2500

Richard Lee3
Prodigy 40 points
Other Parts Discussed in Thread: PGA2500, INA163

This is sorta a follow on from http://e2e.ti.com/support/amplifiers/audio_amplifiers/f/6/t/142591.aspx#

Luis Choey recommends the use of 1n4004GP (glass passivated) diodes in place of the Schottkys recommended in various TI PGA2500 datasheets & App. Notes.

He bases this on http://www.aes.org/e-lib/browse.cfm?elib=15104.  I know from experience that this solution works well replacing Schottkys in INA163.

I'm trying to sort out noise problems on a commercial design that uses PGA2500 with SK12 Schottkys.  The Schottkys go leaky / noisy after some time, for me between 3 mths and a year.  As I'm just repairing my own gear, I can't conduct extensive death tests to prove the efficiency of 1n4004 in protecting the PGA2500.  (I did do this witn INA163 cos that was a product I designed for sale).  I can't afford to kill PGA2500s in my present financial state.

Has TI ever conducted P48V shorting tests on PGA2500 protected with 1n4004s?

  • 0
    TI__Guru**** 189401 points

    Hi, Richard,

    Luis is a little swamped at the moment, but I made sure he is aware of your post.

    -d2

  • 0 in reply to Don Dapkus
    TI__Guru 55466 points

    Hi Richard,


    If I remember correctly, I wired a circuit a while back, similar to the one published on Figure 17 of the article mentioned above using one of the PGA2500 EVM's.  I performed a few tests; but I did not test it extensively.  In the circuit, 4x 1N4004GP diodes with 50 Ohm series resistors were used.  If you think it will be helpful, I could wire the circuit below and test a couple of devices; and let you know the results.  I am currently out of the office and it will be next week until I have access to the bench board.  There are a few different configurations that could be used, however, the designer/user must ensure that the maximum allowed absolute ratings for the PGA2500 device inputs and supplies are not exceeded.

    Thank you and Best Regards,

    Luis

    4276.1N4004GP_FORUM2.pdf

  • 0 in reply to Luis Chioye
    TI__Guru 55466 points

    Hi Richard,

    I found my notes, the circuit I used previously only had the 4x 1N4004GP diodes with the 50 Ohm series resistors at the inputs, similar to figure 17 on the article.  I updated the post above with the correct circuit.

    Best Regards,

    Luis

  • 0 in reply to Luis Chioye
    Prodigy 40 points

    Thanks for your reply Luis.

    The case to test would be PGA2500 with 1n4004 diodes as with 4276.1N4004GP_5F00_FORUM2.pdf but with 1.5 uH inductors across each 50R resistor (as Fig 2 of INA163 datasheet).  If this is OK, it means you can realise the full Low Noise potential of PGA2500 in a well protected circuit.

    I have tried to kill INA163 with the inductors and protection as described and am confident this is a safe configuration for it.  Confirming this for PGA2500 would be good.

    The inductors reduce the series DC resistance for Low Noise so less protection.  But they also reduce the rise time and max. current spike when a rail is shorted so the diodes have a better stab at protecting.

  • 0 in reply to Richard Lee3
    Prodigy 40 points

    My C19 & 20 were also 22u instead of 47u.  INA163 has 1/2 the current noise of the THAT / SSM equivalents so can get away with less capacitance without too much noise rise at LF.

  • 0 in reply to Richard Lee3
    Prodigy 40 points

    Can't find any indication of current noise for PGA2500

  • 0 in reply to Richard Lee3
    TI__Guru 55466 points

    Hi Richard,

    Thank you for letting me know the details about the protection circuit.  I will go ahead and perform some tests using the PGA2500 with the protection circuit described (4x 1n4004 diodes; with the1.5 uH inductors across each 50 ohm series resistor).  I will have access to the PGA2500 bench board/EVM next week; I expect to provide you an update by middle next week.

    Thank you and Best Regards,

    Luis