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TMS320F28075: Questions related to absolute maximum rating

Sheldon He
Expert 8585 points
Part Number: TMS320F28075

Hi expert,

I have three questions related to understanding the absolute maximum rating on C2000 devices.

Q1: For F28075 device, a Input clamp current ABS value is +-20mA, but it noted in the DS that "Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability." So, how long can it stands a 20mA current without damaging the device? The unit is "us", "ns" or "s"?

Q2: For F28075 device, Input clamp current "input current per pin" and "total for all input current" is the same 20mA. If the total limit is already set, why we need a "per pin" value?

Q3: For F28069 device, there is a "Continuous clamp current per pin is +-2 mA." Why we didn't see this on F28075? Is there a same limit on F28075?

Hope there is a FAQ for ABS value related questions. In field team, customers always want these answers for evaluate risks in worst conditions.

: )

Thanks

Sheldon

  • 0
    TI__Guru* 95315 points

    Sheldon,

    Jason Whiles has addressed this on multiple threads. A sample is below:

    You can get more links by searching the e2e with “clamp current” and “Jason Whiles”

  • 0 in reply to Hareesh Janakiraman
    TI__Expert 8585 points
    Hi Hareesh,
    Thanks for your reply. I searched around but not all of my question can be answered.
    In this post, you mentioned 20mA limit is for "transient", so, how long is a "transient"?
    e2e.ti.com/.../2239121
    BTW, for my Q2 and Q3, especially Q3. Hope you can still give me some answer.
    Thanks!
    Sheldon
  • 0 in reply to Sheldon He
    TI__Expert 5160 points

    Sheldon,

    Q1: For F28075 device, a Input clamp current ABS value is +-20mA, but it noted in the DS that "Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability." So, how long can it stands a 20mA current without damaging the device? The unit is "us", "ns" or "s"?

    >Jason> Any exposure to 20mA current should be transient only (us or ms).  This includes overshoot from reflections or a transitional current limited current injection.  The Absolute Maximum should not be kept active for seconds or minutes repeatedly.

    Q2: For F28075 device, Input clamp current "input current per pin" and "total for all input current" is the same 20mA. If the total limit is already set, why we need a "per pin" value?

    >Jason>  For example if there is 5mA injection on 10 pins this would be 50mA and violate this rating.

    Q3: For F28069 device, there is a "Continuous clamp current per pin is +-2 mA." Why we didn't see this on F28075? Is there a same limit on F28075?

    >Jason> The continuous current rating of 2mA per pin on F28069 was different way to indirectly communicate the "total for all input current" limit of 20mA.  This is not a 1:1 replacement so do not try to be very precise on this one, but this was the general intent.

    Best regards,

    Jason

  • 0 in reply to Jason Whiles
    TI__Expert 8585 points
    Jason,

    Thanks for your help. BTW, for F28075 device, it will not withstand a continuous 3mA current on one of the ADC pin right?

    Sheldon
  • 0 in reply to Sheldon He
    TI__Expert 5160 points
    Sheldon,

    From a reliability standpoint that is borderline. The 3mA is not too high and if only on one pin then it should not cause any catastrophic failures.
    We do not put the ADC pins in such a condition for extended duration testing so I can not say if the device functionality would be degraded progressively over time. I do not think it will be a problem but would hesitate to recommend this as an acceptable device configuration for a DC condition.

    From a functional standpoint this will cause problems. Current injected into the ADC inputs will go to the VDDA supply which will have a noise impact on all of the ADC, DAC, and Comparator performance characteristics. For this reason alone this should be avoided except in transient fault conditions when functional operation is not required.

    Best regards,
    Jason