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TPA3111D1EVM: AVCC slew rate

Jonathan Gudelski
Prodigy 50 points
Part Number: TPA3111D1EVM

I create a design based off of the TPA3111D1EVM reference schematic for the TPA311D1PWPR audio amplier. The 10 ohm 1/4 watt resistor would randomly burn up on some boards.  Looking at the datasheet for TPA3111D1PWPR it is recommended that 100K ohm resistor be put in series with AVCC.  Figure 17 however only shows a 100k ohm resistor in series with pin 14 and not pin 7.  Is this the correct wiring?  The slew rate of AVCC is in the microsecond range. Are these ICs considered damaged at this point since this exceeds the microsecond specificiation?  

Thanks

  • 0
    TI__Expert 6985 points
    Hello Jonathan! Shawn will take a look at your question. Also, just so we are clear you are using the schematic of the EVM, correct? Also, what is your Supply voltage and what is the load that you are driving? Thanks, Jeff
  • 0 in reply to Jeff Kohnle
    Prodigy 50 points

    Hi Jeff, I attached the schematic that we are using.  As you can see there isn't a 100k resistor in series with AVCC.  The MAIN_PWR_RAIL is anywhere from 16.7V to 11V and we are driving a 4 ohm load (Goldwood P/N GW-204/4S).  The slew rate at power up is around 200V/msec. Thanks for the quick response!

  • 0 in reply to Jonathan Gudelski
    TI__Mastermind 24835 points

    Hi Jonathan,

    In Figure17 in the datasheet, one 10ohm resistor between PVCC and AVCC is used to keep the high frequency noise from entering linear analog circuit. And there is also 100kOhm resistor used for pin #14. Becasue pin #14 is not a power supply input pin(different from pin #7), it's actually an analog input control pin. So the 100kOhm resistor is used to protect the pin when the PVCC slew rate is too high. Usually the resistor is necessary when the slew rate is larger than 10V/ms.

    Best regards,

    Shawn Zheng   

  • 0 in reply to Shawn Zheng
    Prodigy 50 points

    Hi Shawn,

    What is the failure mode if the the 100K ohm resistor is not in series with pin 14 and there is a large slew rate? We have seen the 10 ohm 1/4 watt resistor burn. One test was performed with the 10 ohm resistor replaced with a 0 ohm resistor which causes a catastrophic failure of the IC after a few power on cycles (less then 10). I'm assuming/hoping the 100k ohm resistor will resolve these issues.
    Thanks

  • 0 in reply to Jonathan Gudelski
    TI__Mastermind 24835 points
    Hi Jonathan,
    If there is no 100kohm resistor and the slew rate is very high on pin #14, the pin is probably damaged. Could you please measure the voltage on the pin #14? Is it the expected? If this pin is damaged and driven to a low voltage, the current on the 10Ohm resistor would be very high, which probably makes the resistor burn. Please keep in mind, the 100kOhm resistor is necessary if the AVCC slew rate is large.
    Best regards,
    Shawn Zheng