SN74LVTH16244A: different output when input pin floating

Johnny Guo

Part Number: SN74LVTH16244A

Hi, team,

I met one issue in my customer side. They have two boards with SN74LVTH16244A on board with similar design and layout. If they disconnect SN74LVTH16244A input pin connection, they can find devices output on one board is always HIGH and is always LOW on another board. I checked the result, no obvious difference can be found on this two boards, and if doing A-B-A swap test, the output still went with board.

I checked SN74LVTH16244A datasheet and "Implications of Slow or Floating CMOS Inputs", for floating input, the device output should be random HIGH or LOW.

Could you help give me more suggestion to explain this? is it possible to be related with power supply or something else?

Thanks.

Johnny

over 7 years ago

0 Dylan Hubbard over 7 years ago

TI__Mastermind 46065 points

Hi Johnny,

I am happy to help. Could I get a schematic for both boards to help me verify the issue?

0 Johnny Guo over 7 years ago in reply to Dylan Hubbard

TI__Expert 4910 points

Dylan,

I have no schematic from customer, but we have already disconnected the input and output pins with other connections.

We found that a long floating wire connecting with input will influence the output. Our suspicion is the noise coupled into floating wire will affect the output.

Thanks.

Johnny

0 ShreyasRao over 7 years ago in reply to Johnny Guo

TI__Guru 62280 points

Johnny,

Please refer to the bus hold app note to understand more about the internal bus hold circuitry.
www.ti.com/.../scla015.pdf

The input circuitry forms a weak latch to keep the last known state through a feedback circuit.
are both the boards have same last known states?

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SN74LVTH16244A: different output when input pin floating