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TAS5706A power up initialisation

Neil A Quarmby
Intellectual 455 points
Other Parts Discussed in Thread: TAS5706A

Hi, I have a design that has two TAS5706A parts on it with slightly different layout and routing of the power and signals. When I apply +24V power to the design only one of the amps works as expected. If I lower the input supply voltage to 10V then both amps work as expected. The 3.3V rail is derived from the main supply so ramps up slightly behind it in time. I note that some of the TAS amps need a power supply sequence of 3.3V first, this is hard to do without getting a custom power supply built, it is much easier to derive the 3.3V from the main rail.

Do you have any hints on where to find the answer to this problem?

Neil

  • 0
    TI__Guru**** 189399 points

    Hey, Neil,

    This is odd. Have you cut in an external 3.3V supply to verify that it's a sequencing problem.

    Are you using the same I2C address for both chips? I don't remember if we offer two addresses for this part, but if not, we do not recommend having two devices on the same I2C bus with the same address...

    -d2

  • 0 in reply to Don Dapkus
    Intellectual 455 points

    Don, when I do use an external 3.3V rail then at least one of the prototype boards does work with 24V applied a few seconds later.

    The two devices are on different I2C busses.

    I am trying to avoid a power switch in the 24V rail or a more complex psu with two sequenced outputs.

    Any suggestions?

    Neil.

  • 0 in reply to Neil A Quarmby
    TI__Guru**** 189399 points

    Neil,

    How odd... I am not really aware of any supply sequencing problems with these ICs, and most of the customers I work with generate the 3.3V off the 24V, as we do on some of our EVMs as well...

    Can you read the I2C from the "dead" IC? Read 0x00 and you should get 6C (I'm Alive). 

    Is the output of the "dead" IC switching? If so, what freq? Is it in "limp" mode?

    -d2

  • 0 in reply to Don Dapkus
    TI__Guru**** 189399 points

    Neil,

    I discussed this with one of my guys (who is needless to say more knowledgeable...).

    He gives this advice:

     

    Typically we should hold reset low until all power rails are settled, i.e. don’t send any I2C commands until then.

    I hope this helps...

    -d2

    PS As I write this, logged into the forum, hurtling across Japan at 300 km/hr on the shinkansen! Ain't technology grand?

     

  • 0 in reply to Don Dapkus
    Intellectual 455 points

    Don, thanks for spending some time to look at this problem. The outputs are 'limp' and no significant current is drawn by the failing amp. I have tried to follow the datasheet sequence so that all signals are low during power up with resistors pulling lines low until the microcontroller wakes up (except for I2C bus pull-ups). I then put PDN high and MUTE high and 5ms later release RESET. The clocks are only present after the release of RESET. I wait for 15ms before I send the oscillator trim command. Then I wait for 50ms before setting all of the other registers.

    Any further thoughts?

    Neil.

  • 0 in reply to Neil A Quarmby
    Intellectual 455 points

    Don, it looks like it is a layout issues with significant noise on the ground plane during start-up. By adding some extra wires to my board, it has started to work as expected.

    Thanks again,

    Neil