SN74LVC2T45: Output spike issue

Jejomar Ildefonso

Part Number: SN74LVC2T45

Hello Team,

Requesting your help on this.Our customer is having issues with the SN74LVC2T45 output. The device are used to translate signals from 3.3V to 5V level. However, output spikes appears upon its power-up.

Attached are waveforms and additional information.

He confirmed that they have followed the correct supply and power-up sequence recommendations given on the datasheet.

We would really appreciate any help.

Regards,

Jejomar

SN74LVC2T45 spike issue.pptx

over 4 years ago

0 Dylan Hubbard over 4 years ago

TI__Mastermind 42600 points

Hi Jejomar,

Can I also get the input probed in that scope shot?

0 Jejomar Ildefonso over 4 years ago in reply to Dylan Hubbard

TI__Expert 8590 points

Hello Dylan,

Thank you so much for looking into this. Here is another waveform which includes the input.

Ch1: 3.3V supply
Ch2: 5V supply
Ch3: SN74LVC2T45 input
Ch4: SN74LVC2T45 output

Regards,

Jejomar

0 Dylan Hubbard over 4 years ago in reply to Jejomar Ildefonso

TI__Mastermind 42600 points

Hi Jejomar,

Thank for the additional scope shot. These translators due to their architecture can glitch during power up. Will this cause any issue with the device downstream?

0 Mohammad Karimi over 4 years ago in reply to Dylan Hubbard

Prodigy 30 points

Hi Dylan,

Unfortunately having spike at some discrete outputs are not acceptable.

Regards,

Mohammad

0 Dylan Hubbard over 4 years ago in reply to Mohammad Karimi

TI__Mastermind 42600 points

Hi Mohammad,

I would try adding a weak pull-down to the output as well (10 Kohm will do). Keeping the input and output at a defined state during power up may help with this glitching.

0 Mohammad Karimi over 4 years ago in reply to Dylan Hubbard

Prodigy 30 points

Hi Dylan,

I have put the pull down at both input and output.

The waveforms that I sent are captured with 1.6K pull down at input and output. The text in the submitted waveform shows that.

Thanks,

Mohammad

0 Dylan Hubbard over 4 years ago in reply to Mohammad Karimi

TI__Mastermind 42600 points

Hi Mohammad,

Unfortunately, that's my best suggestion to eliminate eliminate the glitch. Like I said previously, this glitching is inherent due to the architecture of Direction-controlled translators. We have a new family designed specifically to be glitch free during power up which is our AXC family, but it only operates up to 3.6 V.

0 Mohammad Karimi over 4 years ago in reply to Dylan Hubbard

Prodigy 30 points

Hi Dylan, Jejomar

Understood....

Unfortunately I have to change the design and re-layout the boards that costs the company quite money to re-do this; let alone the schedule to meet the milestones.

I wish TI had put a note in datasheet and warned the user that the chip could have this potential issue.

Thanks for your support.

Mohammad

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SN74LVC2T45: Output spike issue