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TAS5630B start-up issue

Marco Ferretti
Prodigy 140 points

Other Parts Discussed in Thread: TAS5630B

Hi all-

I am experiencig a start-up issue on a TAS5630B (DKD package, PBTL mode) borad I am working on. This a revision of a previous version of the board (that performned perfectly) where minor changes have been made. These changes did not involve the TAS563B routing on power sypply and output pins.

On the new board release, when feeding power, the device will start occasionally, but most of the times it will not start oscillating and SD and READY pins will remain low, even with outputs disconnected (no load) and zero input signal

Schematic and component values are identical to datasheet's reference design.

According to the datasheet's statements, the device has PPSC (chapter 7.3.5) and this was my first investigation. I have carefully checked for a possible condition that may trigger the PPSC and did not found any.

Still I belive the that the PPSC is triggered for some reasons because the device does not respond to a toggle on the reset pin.

Or maybe I am not looking in the right direction...

Any suggestion is welcome

Thanks for your support.

Marco

  • 0
    TI__Genius 9175 points

    Hello Marco,

    Have you monitored SD and the OTW pins as shown in section 7.3.3 in the datasheet?
    These pins should indicate if there is a problem. Monitoring these on a scope is the best way to track the timing of the pins.

    I would also recommend checking VDD, GVDD, and PVDD voltages.

    Are you experience this issue on more than one board?
    Have you swapped devices?
    Any changes in the startup sequence between the two boards?

    If you have a schematic that would be very helpful.

    Best Regards,
    Matt

  • 0 in reply to Matthew Beardsworth
    Prodigy 140 points

    Dear Matt, 

    sorry for my late reply. I thought I fixed the issues to the amp, but still I'm having troubles with it....

    I have posted here both schematics and pcb layout.

    The application is a voice alarm equipment (fire alarm and control systems...). The amp is matched to a 100V loudspaker line with a toroid transformer that, in atiditon, grants full isolation.

    Also, on the secondary side of the transformer a relay will disconnect the line under certain conditions (loudspeaker line shorted and/or line earthed).

    The amp is powered by a linear power supply. Rail is 50V nominal, 52V absolute max.

    On the inputs side, there is full isolation on both audio (transformer) and logic signals (optos).

    Now, if I get a NIB amp assembly and power it with lab power supply, idle current is about 180mA, the amp modulates and all control signals indicate the amp is alive. If I hold the reset, idle current drops to abuot 15mA, nSD pin moves to the shudtown condition, but the nRDY pin tells the amp is in the ready condion.

    If I remove the rest, the amp gets back to modulate. So far, so good.

    Now, for some reason I still do not understand, if I stress the amp by unpowering it, and powering it up again (no input signal, with or without load, - no difference) after a random number of times, the amp will not start modulating, it starts stuck with nSD-high, nOTW-hign, but nSD-low. Idle current is 15mA and nRES toggle has no effect.

    No way to get it back to start again. If I remove the TAS3060B from the board and install a new one, the amp gets working...

    Seems like there is something that damages the IC during power up / power down

    Any idea would be so helpful!

    Thank you very much for your support

    Best regards,

    Marco

    VA301_PCB.pdf

    VA301PWA_SCH.pdf

  • 0 in reply to Marco Ferretti
    Prodigy 140 points

    Hi Matt,

    some additional info:

    both nSD and nRDY pins get stuck low when the amp fails to start. In that conditions, loudspeaker outputs are +10V above GND.

    This morning, powered some of the amps that refused to start two days ago. I was about to change the TAS5630B from the board, but before I though it was a good idea to give them them a try.

    One of them started immediately, another started modulating about 5s after power-up. The last two did not start at all..

    I'll keep on investigating...

    Marco

  • 0 in reply to Marco Ferretti
    TI__Genius 9175 points
    Hi Marco,

    Sorry for the delay I was traveling in Asia for the past two weeks.

    I didn’t realize the amplifier was transformer coupled. This likely the source of your problems.

    1. If the core of the transformer is too small, it will easily saturate at low frequencies. This will cause the impedance of the transformer to fall off and the amp will operate into a very low impedance load during saturation which may cause a damaging over current event. Our amplifier usually require a minimum output inductance even during on OC event to limit the rise time of the output current. Make sure to limit the amplifier low frequency bandwidth using input DC blocking caps. The higher you can set this pole the better.

    2. Toroidal transformers are notorious for saturation even with only a slight DC offset across the primary regardless of core size. On startup if the Class-D outputs across the primary do not ramp 100% symmetrically, the toroid will saturate. EI transforms can handle imbalances much better. It may be worth giving an EI transformer a try.

    3. Check The Class-D output current and voltage levels during startup/shutdown and playing the audio. Inductive kickback or saturation evens may cause spikes in the output voltage and current from the class-D, killing the amplifier.

    I hope this helps,
    Matt