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TAS5421-Q1: TAS5421-Q1 problem: 7 ohms measured between SDA-SCL and GND

Jean-Michel THOORENS
Prodigy 70 points
Part Number: TAS5421-Q1
Other Parts Discussed in Thread: TAS5421EVM, STRIKE

Hi Team,

I use TAS5421-Q1 without I2C and without FAULT output.

In this case, the technical document SLOS814D tells us :

p. 8.2.2.1.3 :" If there is no microcontroller in the system, use of the device without I 2 C communication is possible. In this situation, connect the SDA and SCL pins to 3.3 V.

p. 8.2.2.1.4 :" If the FAULT pin does not report to a system microcontroller in the application, connect it to GND."

So I connected these pins according to the indications given.


My module has an auxiliary power supply of 3V6 (TPS70936 ) on which I connected directly SDA and SCL. FAULT is connected to GND
But with some devices, there is a problem with powering up (16.8 V): the TAS5421 does not start. While investigating the circuit I was able to highlight a short circuit between the SDA-SCL and GND (7 ohms).
Question: Do you confirm the informations in paragraph 8.2.2.1?

Thank for your response.

J.M. Thoorens

  • 0
    TI__Mastermind 45085 points

    Hi Jean-Michel,

    Are you sure there is not a voltage spike on the 3.6Vdc at start up of the power that could overvoltage the SDA and SCL pins?  This could cause the some leakage to appear on these pins and is seen as a low resistance.  The device may be damaged. 

  • 0 in reply to Gregg Scott
    Prodigy 70 points
    Hi Gregg,
    I believed that for a moment. So I installed the TPS70936 less than one inch from TAS5421, but some specimens continue to fail at startup...
    And I have not TAS5421EVM to test the configuration described on paragraph 8.2.2.1.3 (SDA-SCL with 0 Ohm pullup resistors).
    My question remains.
    Question n ° 2: by carefully adding 4.7 k pullup resistors on SDA-SCL pins, am I safe from any bad surprises during the startup sequence ?
  • 0 in reply to Jean-Michel THOORENS
    TI__Mastermind 45085 points

    Jean-Michel,

    There may still be a short pulse of voltage, it does not take too much to look like an ESD strike.  The addition of resistors shows that something is occurring on start up.  These resistors stop the current flow so the overvoltage does not damage the device.

  • 0 in reply to Gregg Scott
    Prodigy 70 points

    Hi Gregg,

    You're absolutely right, we're never safe from an ESD strike, me on my module and you on your TAS5421EVM.

    I will therefore add these forgotten pullup resistors to SLOS814D p. 8.2.2.1.3  and solve my problem.

    Best regards,

    J.M Thoorens