SN74AVCH4T245: Ground or float I/O pins?

John Garrett

Part Number: SN74AVCH4T245

Hi All,

I just received this customer question: I have a question about SN74AVCH4T245. What should we do to the unused inputs and outputs? Should we keep floating or ground them?

Note: the data sheet is a bit contradictory here as note 3 on page 5 says ground or tie input pins to Vcc. However, further on in the data sheet it discusses bus-hold circuitry and says its OK they float.

My understanding is we don't usually have an issue with floating output pins in CMOS. Input pins generally need to be grounded. However, the SN74AVCH4T245 input pins can be left floating as they have additional bus-hold circuitry to prevent shoot through.

Please confirm.

Thanks, John Garrett, TI-AFA

over 7 years ago

0 Karan Kotadia over 7 years ago

TI__Genius 16735 points

Hi John,

The customer is correct with their assumptions. The SN74AVCH4T245 does contain a bus-hold feature which allows for the inputs to be left floating. Also as the customer mentioned there isn't an issue with a floating output in CMOS.

Thanks!
- Karan
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0 Karan Kotadia over 7 years ago in reply to Karan Kotadia

TI__Genius 16735 points

Hi John,

I would also mention that the inputs to the direction and enable pins do not have the bus hold feature. So those pins do need to be either grounded or at Vcc.

Thanks!
- Karan

0 John Garrett over 7 years ago in reply to Karan Kotadia

TI__Expert 4220 points

Understood and thanks!

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SN74AVCH4T245: Ground or float I/O pins?