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TAS5825M: Questions regarding Cycle By Cycle (CBC) and Over-Current Error (OCE) fault behavior

John Pierson
Intellectual 320 points
Part Number: TAS5825M

Hello,

I have a couple of questions regarding the CBC Fault and OC Fault behavior of the TAS5825M Smart Amp.

OC Fault

Threshold is 7.5 Amps typ. Is this a peak or peak to peak value? Is this a per channel event or does this apply to both channels? And if the fault condition goes away, a write to register 0x87 will clear the fault and audio will resume on the output of the amp?

CBC Fault

Threshold is 6.5 Amps typ. Is this a peak or peak to peak value? I would like to request clarification of the behavior of this fault. From the data sheet:

"The CBC current-limiting circuit terminates each PWM pulse limit the output current flow to the average current
limit (ILIM) threshold. The overall effect on the audio in the case of a current overload is quite similar a voltageclipping
event, temporarily limiting power at the peaks of the music signal and normal operation continues without
disruption on removal of the overload."

My understanding from the description above is this will NOT shut down / off the affected channel. It will affect the audio. But it will not require a write to register 0x78 to clear this.

Is this correct?

On the other hand, I see Table 55. GLOBAL_FAULT2 Register Field Descriptions:
CBC_FAULT_CH2_I right channel cycle by cycle over current fault
CBC_FAULT_CH1_I left channel cycle by cycle over current fault

So is this a fault that must be cleared by a write to register 0x87?

Max Safe Peak Output Current

What is TI's recommendation for the maximum peak output current the amp should be limited to so that CBC and OC faults will not occur?

Thank you for your help with these questions.

John

  • 0
    TI__Guru 52115 points

    Hi John,

    See my comments below.
    Threshold is 7.5 Amps typ. Is this a peak or peak to peak value?
    [Andy]7.5A (typ) is a peak value.

    Is this a per channel event or does this apply to both channels?
    [Andy] If the current in either channel goes above the 7.5A (typ), an OC fault will be reported and TAS5825M will shut itself down.

    And if the fault condition goes away, a write to register 0x87 will clear the fault and audio will resume on the output of the amp?
    [Andy]Yes. Your understanding is correct. One correction. You need to write to Register 0x78 (not 0x87).

    My understanding from the description above is this will NOT shut down / off the affected channel. It will affect the audio. But it will not require a write to register 0x78 to clear this.
    Is this correct?
    [Andy] In most normal cases, the CBC current-limiting is most likely able to avoid the occurrence of OCSD (Overcurrent Shutdown). However, it cannot guarantee the current is always under control. If CBC is already active for a few certain cycles (I will double check how many cycles) but the current is still going up, a CBC fault will be triggered and TAS5825 will shut itself down. You will have to write to Register 0x78 to clear the fault.

    What is TI's recommendation for the maximum peak output current the amp should be limited to so that CBC and OC faults will not occur?

    [Andy] The CBC is disabled by default. If CBC is off,  the maximum peak output current should be lower than the OC threshold 7.5A (typ). Note that 7.5A is a typical value. 

    If CBC is on, large peak currents in a very short time can be allowed or limited since CBC kicks in when the current is bigger than 6.5A (typ). The maximum peak output current will most likely depend on the music contents.


    Andy