TXB0108: lock B4 to High

Yuta Nishie

Part Number: TXB0108
Other Parts Discussed in Thread: SN74LVC1G125, SN74LVC1G126

Hi,

The customer power sequence is as follows:
1. VCCA, OE=1.8V and VCCB=3.3V are applied
2. After 10s
3. Boots 1.8V processor and 3.3V processor

Customers want to lock B4 to High for 10s from the time 1.8V is applied to the OE until the processor starts.
Is there any good way?

Since there is an internal pull-up resistance as shown in the following material, do not I need to take any measures?https://www.ti.com/lit/an/scea054a/scea054a.pdf?ts=1656689448543&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTXS0104E&_ticdt=MTY4MzY5OTk3M3wwMTc5OWI5OGI4OGIwMDBjZTdhYjY4NzQ5NjM5MDMwNzMwMDI3MDZiMDA5Nzh8R0ExLjIuMTM1MTg0OTI4NS4xNjIxODEzMTQ4

Or should I install a pull-up resistance of more than 50kohm?

Best Regards,

Nishie

over 1 year ago

+1 Clemens Ladisch over 1 year ago

Guru 259840 points

It might be possible if you connect 100 kΩ pull-ups to both A4 and B4. (But the datasheet does not say anything about the start-up behaviour.)

Alternatively, force the input high. Connect the output of a three-state buffer like the SN74LVC1G125/SN74LVC1G126 to A4, and control its /OE or OE input with the reset signal.

0 Yuta Nishie over 1 year ago in reply to Clemens Ladisch

Genius 3230 points

Hi Clemens-san,

Thank you for your reply.

It would be very appreciated if TIer give a comment about Clemens's suggestion?

Best Regards,

Nishie

+1 Michael Ikwuyum over 1 year ago in reply to Yuta Nishie

TI__Mastermind 25560 points

Hi Yuta,

Yes, we do not expect any issues with the suggestion. You may pull the line high connecting the 100K to the supplies and ramp up the supplies first by fixing OE at 0, and then after supplies are ramped up -> push OE to 1.8V or force the input high, thanks.

Best Regards,

Michael.

0 Yuta Nishie over 1 year ago in reply to Michael Ikwuyum

Genius 3230 points

Hi Michael-san,

Thank you for your reply.

I understood as follows, is this correct?

Best Regards,

Nishie

+1 Michael Ikwuyum over 1 year ago in reply to Yuta Nishie

TI__Mastermind 25560 points

Hi Yuta-San,

Yes, I see OE using a different supply. Hence, help ensure VCCA and VCCB supplies are ramped up first then OE, thanks.

Best Regards,

Michael.

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TXB0108: lock B4 to High