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TMS470MF06607: Output current specification of MIBSPIP2SCS[2] and MIBSPIP2SCS[3] pins

Steve Kuc
Prodigy 30 points
Part Number: TMS470MF06607

Tool/software:

SAP Part number S4MF06607BSPZQQ1

Due to a coding error, pins 3   MIBSPIP2SCS[2] and 4 MIBSPIP2SCS[3] are NOT designated as input (as intended) but assert OUTPUT HIGH leading to contention with the circuitry fitted to the PCB as follows:

Pin 3 is tied to ground through a zero ohm resistor. However shortly after power-up PIN3 is commanded high for ~0.55ms 

When the 0R resistor is replaced with 100R in order to measure pin output current the following was recorded:

Pin 4 is configured thus:

The circuit was modified with a 10R resistor in series with TR356 collector (pin3 ) in order to measure the current.

At power-on the measure current is shown below.  Pin4 is asserted high shortly after power up. Current peaks at around 40mA then reduces as C1079 charges up.

The TMS470 data sheet  specifies output currents(s) as  4mA (Adaptive Impedances 4mA buffer), so we recognise that we are operating outside of the datasheet limits during this brief transient period. However over 100's of power on cycles we have not seen any failures.

Q1. Can you provide any further information on the current capability of these pins?

Q2. If we have stressed these pins, would any stress be limited to these pins only or would the whole device now be considered as "over-stressed"?

Any advise you can offer is gratefully received.

  • 0
    TI__Guru**** 191366 points

    Hi,

      I'm out of office until Wednesday. I will look into your question when I come back. Sorry for the inconvenience. 

  • 0
    TI__Guru**** 191366 points
    Steve Kuc said:
    Due to a coding error, pins 3   MIBSPIP2SCS[2] and 4 MIBSPIP2SCS[3] are NOT designated as input (as intended) but assert OUTPUT HIGH leading to contention with the circuitry fitted to the PCB as f

    Hi,

      Are you saying that firmware is frozen and you cannot change it to make these two pins input?

    Steve Kuc said:

    Q1. Can you provide any further information on the current capability of these pins?

    Q2. If we have stressed these pins, would any stress be limited to these pins only or would the whole device now be considered as "over-stressed"?

    You are operating outside the absolute maximum and it may impact the reliability and the longevity of the device. Please either update the firmware if possible or increase the series resistance value to limit the overcurrent on the pins. 

  • 0 in reply to Charles Tsai
    Prodigy 30 points

    Hi Charles

    Indeed we updated the firmware as soon as the problem was realised, and yes we recognise we have been operating outside the absolute maximums.  However given your knowledge of this part is it possible to theorize on the failure modes? Would  any failure be limited to the output devices associated with these pins or could failures occur anywhere within the device ? I appreciate you cannot give any guarantees, this is just to help our risk analysis for equipment still in the field.

  • +1 in reply to Steve Kuc
    TI__Guru**** 191366 points

    Hi Steve,

    Steve Kuc said:
    Indeed we updated the firmware as soon as the problem was realised, and yes we recognise we have been operating outside the absolute maximums. 

    Updating the firmware to rectify the issue is the correct way to handle any potential reliability issue down the road. Unfortunately, we don't have a simulation model to quantify the longevity of the device when the device is subject to out of spec operating condition for a given duration of time and the number of power cycles. What I'm afraid of is that a prolonged current surge over the lifetime and cycles can damage the I/O pad. I just can't provide a guarantee if or when it will ever happen.  Sorry that I can't provide any further guidance.