SN74AXC8T245: DIR2 pin

JDJ

Part Number: SN74AXC8T245

In the datasheet for SN74AXC8T245RJWR it's mentioned that DIR2 pin is applied when both VCCA and VCCB >= 1.4V.
However we can't find the description about device behavior, when DIR2 tied to VCCA (weak pull up 100kR...1MR), but VCCA is below 1.4V (in the range 0.65V...1.39V).
Is true, that in this case device (IC) see it (DIR2) as floating?

over 1 year ago

0 Michael Ikwuyum over 1 year ago

TI__Mastermind 33805 points

Hi JDJ,

Control inputs should never be left floating.

Please note that the device has weak pull-downs internally and external pull-ups for I/Os are recommended to be < 30K ohms.

Please see [FAQ] Why is there a voltage offset at the input of the SN74AXCxTxxx device?

If DIR2 is tied to VCCA 0.65V to 1.39V, table 1 will still hold, thanks.

Best Regards,

Michael.

0 JDJ over 1 year ago in reply to Michael Ikwuyum

TI__Expert 3831 points

What is the range of weak pull-down inside the device, around 300kR?

If next statement is correct : "If DIR2 is tied to VCCA 0.65V to 1.39V, table 1 will still hold."
Can you explain a bit supply remark in the pin table (see pic attached)?

0 Michael Ikwuyum over 1 year ago in reply to JDJ

TI__Mastermind 33805 points

Hi JDJ,

Yes around 300K ohms for the 8ch device.

I will also work internally to help update the datasheet, thanks.

Best Regards,

Michael.

0 JDJ over 1 year ago in reply to Michael Ikwuyum

TI__Expert 3831 points

To clarify is the information in the red box needs to be updated since "If DIR2 is tied to VCCA 0.65V to 1.39V, table 1 will still hold."?

0 JDJ over 1 year ago in reply to JDJ

TI__Expert 3831 points

Also, is this Pull Down connected permanently or only when VCCa is below UVLO?

0 Michael Ikwuyum over 1 year ago in reply to JDJ

TI__Mastermind 33805 points

Hi JDJ,

Yes your clarification is accurate. I am also checking internally with the datasheet author just to help further double confirm.

Are you observing otherwise, as-is?

Also, the pull-down turns on when the drivers are disabled either by not having any of the supply voltage above UVLO or disabled by output enable pin (OE) to help drive and keep low any floating inputs, thanks.

Best Regards,

Michael.

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SN74AXC8T245: DIR2 pin