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SN74LVC2T45: Is this part or part packages (DSBGA) light sensitive

Terry Hipp
Prodigy 50 points
Part Number: SN74LVC2T45

We are using the SN74LVC2T45YZPR part in a battery design and have noticed that our current draw is sensitive to light exposure.  We believe we have tracked this issue down to the SN74LVC2T45 parts.

Looking through the forum topics, I see there are potential light sensitivity issues with the DSBGA package.

Does the SN74LVC2T45 have a light sensitivity issue?  Would this be considered a component or package issue?  Is there any additional data or application notes that detail this issue?

Regards

Terry

  • 0
    TI__Guru 50366 points

    Hi Terry,

    The level shifters are not sensitive to light with no known light sensitivity issue.

    I would recommend verifying the device is not damaged (from exceeding the absolute max ratings) by replacing with a known good unit. If not the case, please further help clarify and highlight the observed topics with the potential issues, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 50 points

    Hi Michael,

    We have no reason to believe the devices are damaged as our board is othewise working as expected. 

    We notice the light sensitivity issue when only one rail of the SN74LVC2T45 (either VCCA or VCCB) is powered.
    We have used various light sources with laser pointer accuracy, so we are fairly confident the SN74LVC2T45 is the offending IC. Additionally placing electrical tape over the ICs eliminates the issue. Enough energy is created to trigger an interrupt on processor IO lines that utilize the SN74LVC2T45 for voltage translation.  Most of the current draw we experience is likely due to the interrupt activity so the effect may be very transient.  We do use 0.1µF decoupling caps on both VCCB and VCCA of the chip. Our processor IO is 3.3V and we are translating to/from both 5V and 1.8V IO.  

    Regards

    Terry

  • 0 in reply to Terry Hipp
    TI__Guru 50366 points

    Hi Terry,

    To clarify, are you indicating the LVC device observes glitches only when either VCC is powered?

    Also note that, per the device's Vcc Isolation feature, all outputs will be in high impedance spec'd for 2uA max. Could you help provide waveforms?

    Additionally, by processor IO at 3.3V; would this be connected to the 5V side of the LVC device or the 1.8V? Do you observe the issue when both VCCA and VCCB are fully ramped up?

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 50 points

    Hi Michael,

    The problem only occurs when either VCCB or VCCA (or both) are NOT powered.  My theory is enough energy is somehow injected into the part which causes a glitch on the IO lines to the processor.  No issues are observed when VCCA and VCCB are fully ramped up.  This probably won't be investigated further as our PCBA is enclosed in plastics that will block light so this is only an issue for testing.

    I was just curious if there was a known issue with the part or part package that we should consider if we ever spin this board.

    Thanks  for looking into it.

    Terry

  • 0 in reply to Terry Hipp
    TI__Guru 50366 points

    Hi Terry,

    Understood. However, I haven't observed similar concerns. Hence, no known issues thus far for our devices. 

    Although, I see similar concerns specific to the package for other devices outside our portfolio similar to your theory.

    Hence, most likely a package issue similar to the below, thanks.

    Best Regards,

    Michael.