MCP4822 fried - possible reason (?)

Discussion in 'General Electronics Chat' started by atferrari, Nov 25, 2012.

  1. atferrari

    Thread Starter AAC Fanatic!

    Jan 6, 2004
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    Testing a DAC MCP4822 (data sheet here) I noticed it hot to touch with 2V at the A output. Last settings transmitted through the SPI interface were to have just 0,5V at VoutA.

    Additional consumption current with that IC in-circuit was as of about 50 mA. No surprise it was hot.

    After discarding a short, I found that:

    • VoutA - pin 1 (and VoutB - pin 3 for the case) had no load resistors.
    • Both outputs had 4u7F tantalium caps as filters.
    • The software had an error that never latched VoutA when values were being progressively decreased. In other words, after going high, VoutA never came down.
    • The test I designed, involved cyclic alternative reset of both outputs, starting with very low values. There, VoutA was effectively (and abruptly) updated.
    I corrected all that and the new chip works OK with a consumption of around 1,5 mA.

    From all the above, what could be the reason for the damage? Maybe the abrupt changes with a big charged cap at the output and no resistor to drain it?

    I expect to learn something from all this. Comments are welcome.

    Successful design, let me tell you...:eek:
     
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