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SN74LVC1G3157: SN74LVC1G3157 troubleshooting

Alexandru Ilinca
Prodigy 105 points
Part Number: SN74LVC1G3157

Hello,
We are using SN74LVC1G3157 in our projects and we found some issue listed bellow.

  1. Output "A" = 1.21V, when PIN "S" = 3,3V and even when PIN "S" = 0V
  2. Output "A" = 0V, when PIN "S" = 3,3V and even when PIN "S" = 0V
  3. Output "A" = 0,54V,when PIN "S" = 3,3V and even when PIN "S" = 0V.

The measuemntes of the impedence suggest that the components are damaged.

Our configuration is Vcc=5V, B1=3.3V, B2=1.8V, S=0 or 3.3V.

We noticed on the datasheet that the Vih_min = 3.5V.

Refering to this we have a few questions?

1) What  are the problems we encounter when driving pin S with a slightly lower voltage?

2) Could this be the cause of the damage of the component?

3) If yes on question number 2, how could it be possibile since we not exceed the Absolute Maximum Ratings?

thanks in advance for the support.

A.I.

  • +1
    Guru 317150 points

    1. The S input might not be read as high. The supply current will increase, and there might be oscillations; see [FAQ] How does a slow or floating input affect a CMOS device?

    2. Maybe. But I cannot rule out overvoltage on some other pin.

    3. You are violating the recommended operating conditions, so the device is not guaranteed to work correctly while the invalid voltage is present. If the resulting currents (shoot-through currents, and increased power usage due to oscillations) become high enough, they will violate the current/temperature limits and damage the device; I do not know how likely this is.