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SN74LVC1T45: Failure of level translator IC : SN74LVC1T45QDCKRQ1

Smitha R
Prodigy 30 points
Part Number: SN74LVC1T45
Other Parts Discussed in Thread: SN74LXC1T45-Q1

Hi,

we are using SN74LVC1T45QDCKRQ1 IC in our design to translate 3.3V data signals to 5V TTL level signals. we are seeing failures of SN74LVC1T45QDCKRQ1 IC.  Details below.

VCCA : 3.3V, VCCB: 5V (5V to 3.3V LDO - we are using to give VCCA). So as per datasheet - to power up VCCB first is being followed. 

DIR is pulled to 3.3V directly.

Problem statement: Recently we have come across 3 board failures in which this IC is damaged with burnt marks on it and on PCB (images shown below). VCCB pin to GND found short in all the cases. This is the only component failed in the board.

We tried to replicate the issue by supplying the VCCB voltage to its maximum recommended operating range of 5.5V and also its abs maximum rating of 6.5V. we could not replicate the issue. On our board also, maximum VCCB power rail can go till 5.3V only.

Input signal to this level translator IC is from Microcontroller output pin (Open drain configuration having internal pull up) through 510 Ohm series resistor. Rise time of the input pulses at pin 3 of IC is around 4.4uS. 

 With these details, can you please let us know what would be the probable causes of U1 IC failure & what other inputs required? Please consider it as priority and support.

  • 0
    Guru 318050 points

    The rise time violates the Δt/Δv limit. I do not know whether this is the cause of the problem, but you are certainly running the device outside its recommended operating conditions, and you are likely to get oscillations at the output. Use the SN74LXC1T45-Q1, which has Schmitt-trigger inputs.

    In general, the most likely cause would be overvoltage (at any pin). I do not know if there is noise on any of these traces.