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SN74LVC2G17DBVT burns

Michel LIENHARD1
Prodigy 40 points
Other Parts Discussed in Thread: UCC27517, SN74AHCT1G125

Hi,

We have 2 buffers from the same IC connected in parallel. P/N is  SN74LVC2G17DBVT.6170.schematic.pdf

Output load is 50 Ohms after 1m cable + polyswitch. (see attached schematic)

Sometimes, the buffer burns.

Then output signal swing is 2V to 5V, instead of 0V to 5V.

* Is it allowed to have 2 buffers in parallel ?

* We source or sink 100mA. Normally 50mA for each buffer. Is this OK ? (according to absolute maximum ratings)

Best regards

Michel

  • 0
    Guru 316510 points

    It is allowed to parallel CMOS outputs.

    However, there is no guarantee that the current is shared exactly equally. And the absolute maximum rating of 50 mA is a value you should stay away from if you do not want to reduce reliability.

    I would parallel four outputs. However, even those will still have a certain output impedance.

    Try a brute force gate driver like the UCC27517 (which does not need the SN74AHCT1G125 level shifter); it has an output impedance of 6 Ω (sourcing) or 0.6 Ω (sinking).