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TCAL9539-Q1: Inputs with schmitt trigger?

Theo Keinarth
Intellectual 375 points

Part Number: TCAL9539-Q1
Other Parts Discussed in Thread: SN74LVC1G02

Tool/software:

Hi TI Team

Do the inputs of this IC have schmitt triggers? I will have low transition times (> 1ms) on some of the input signals in my current project.

Thank you in advance!

Regards Theo

  • 0
    TI__Guru 56048 points

    Hi Theo,

    The Pxx GPIO pins are not Schmitt trigger inputs. However, we do have an interrupt latch register featured on this device. This helps to control the input state change regardless of whether the input reverts back to its original state. 

    What is implied when having low transition times >1 ms. How would this affect inputs w/o schmitt trigger? 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Intellectual 375 points

    Hi Tyler

    In most cases logic ICs have CMOS inputs (like SN74LVC1G02). If there is a voltage applied that is between VI- and VI+ the output stage is sourcing and sinking at the same time (shot through) which can damage those ICs if the transition from low to high or vice versa is to slow. I have no idea if this is also the case for the TCAL9539-Q1. A schmitt trigger resolves this problem with logic ICs.

    If the TCAL9539-Q1 has no problem with voltages between those trigger points it will be fine even if there aren't schmitt trigger.

    Regards Theo

  • +1 in reply to Theo Keinarth
    TI__Guru 56048 points

    Hi Theo,

    I understand your question more clearly now with 1ms ramps. All of our I2C IO expanders have CMOS inputs on the Pxx pins. 

    A mid-rail voltage between VCC and GND on the input will result in higher current draw through the ICC pin due to shoot-through, but should not result in damage to the pin. 

    Regards,

    Tyler