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TMS570LS3137: TMS570LS3137 input signal slew rate

_Frank_
Prodigy 120 points
Part Number: TMS570LS3137

Hello,

datasheet of TMS570 provides Vhys parameter as input hysteresis voltage. So a schmitt trigger structure might be assumed for TMS570 I/Os. If yes, there should be no slew rate requirement for input signals. In other words, is there a timing requirement about the maximum tolerated duration to toggle input signals? Figure 5.2 of data sheet specifies only the minimum pulse width.

Thanks in advance.

 

  • 0
    TI__Guru 59540 points
    Frank,

    Out datasheet identify VIH and VIL parameters that show the voltages at which the transitions from a high to a low will be read. The values in between are sort of a no man's land where the value would be indeterminate. For very long slew rates, this area could be significant meaning the device might read either a 1 or 0 dependent on semiconductor manufacturing properties/process, voltage levels, and temperature. This may lead to inconsistent performance from unit to unit across voltage and temperature.

    The minimum pulse width specification is related more the maximum response rate of the switching within the IOs to handle the transitions from low to high. Smaller pulses may be missed simply because the pulse becomes flattened out due to response of the IO structure.
  • 0 in reply to Chuck Davenport
    Prodigy 120 points
    Dear Chuck,

    thanks for your reply. I’m not worried about indeterminated input logic states. My concern is about the risk to harm the input circuitry if the input voltage of a port pin needs to much time to pass through the voltage range between ViLmax and ViHmin and causes internal destructive currents.

    Best regards
    Frank
  • 0 in reply to _Frank_
    TI__Guru 59540 points
    Hi Frank,

    During the indeterminate range, there could be additional current consumed but this current is very, very small and would, most likely, only be noticeable when the device is in a low power mode. Otherwise the additional current would be lost in the general operating current fluctuation and is in no way harmful to the IO structures.