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Relation between poor Signal Integrity (Signal Overshoot and undershoot) and Device Reliability

rajeeva gk37
Prodigy 120 points
Other Parts Discussed in Thread: TMS570LS3137

Hi,

In the current design we are observing some signal overshoot and undershoot for the TMS570LS3137 interfacing with some external devices (DAC, NVM,ADC).

The overshoot and undershoot are in the order of 0.5V to 1V for 3.3V interface. 

We plan to fine tune the termination resistor to reduce the SI issue in is next build, not possible in the current hardware build. 

However, over a period of time is this Overshoot and Undershoot reduce device reliability? 

with regards

Rajeeva GK

  • 0
    Guru 92251 points

    rajeeva gk37 said:
    The overshoot and undershoot are in the order of 0.5V to 1V for 3.3V interface. 

    However, over a period of time is this Overshoot and Undershoot reduce device reliability? 

    This is not an official answer based upon knowledge of the TMS570LS3137 silicon, but from read of the TMS570LS3137 datasheet SPNS162C.

    The datasheet section 5.8 Input/Output Electrical Characteristics has a Input clamp current (I/O pins) parameter which shows the I/O pins have diode clamps which will conduct if the input voltage is less than Vss - 0.3V or greater than Vccio + 0.3V. My guess is that if the signal overshoot and undershoot doesn't cause the Input clamp current to exceed the per pin recommended maximum current (+/-3.5mA) or the total absolute maximum rating (+/-40mA) then there will be no reduction in device reliability.

    The analysis of the Input clamp current due to signal overshoot and undershoot will depend upon the number of inputs switching, and the current drive capability of source devices driving the input signals.

  • 0 in reply to Chester Gillon
    TI__Guru 68920 points

    We don't say how the device will perform if used outside of it's recommended operating conditions and the overshoot here would be outside of the absolute max voltage spec if 0.5 to 1V above VDD.       The absolute max current spec is in additon to the voltage spec and is summed over all the pins on the device.  It's there because even if you meet the voltage spec on one pin, if you inject current on a large number of pins at the same time this can be an issue even if the abs max votlage spec is met,  going over either spec is a problem. 

    The datasheet gives these statements about abs. max.  

    (1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. (2) Maximum-rated conditions for extended periods may affect device reliability. All voltage values are with respect to their associated grounds

    Which are pretty much as good as it gets.   

    So yes I would say in this case you can expect device reliability to be affected because the overshoot exceeds the absolute max spec... ;  but by how much and how quickly we don't provide a way to predict. 

    -Anthony