TXB0108: Pull-up/Pull-down of input pin

Atsushi Takahashi

Intellectual 675 points

Part Number: TXB0108
Other Parts Discussed in Thread: TXB0304

Hi Team,

I have two questions about pull-up/pull-down of input pin.

1) Is it okay to pulled up/down the input pin? Or is it not recommended?

2) If it is no problem, please tell me how to decide pull-up/down resistor value.

According to the datasheet, pull-up/down is not recommended for output pin, but there is no information about input pin.

Best Regards,

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 243920 points

Section 8.3.5 of thedatasheet says:

If pullup or pulldown resistors are connected externally to the data I/Os, their values must be kept higher than 50 kΩ to ensure that they do not contend with the output drivers of the TXB0108.

0 Atsushi Takahashi over 1 year ago in reply to Clemens Ladisch

Intellectual 675 points

Thank you for your reply.
I think that is about output side.
How about input side?

0 Clemens Ladisch over 1 year ago in reply to Atsushi Takahashi

Guru 243920 points

The TXB is bidirectional; all data pins are outputs.

0 Atsushi Takahashi over 1 year ago in reply to Clemens Ladisch

Intellectual 675 points

I’ｍ sorry for my poor explanation.
Either A1-8 or B1-8 should be an input.
Is it ok to pull-up/down it when using it as an input pin? Or is it not recommended?

Section 9.2.2 of the data sheet says as follow but it is not mention about pull-up/down of input side.
• Output voltage range
- Use the supply voltage of the device that the TXB0108 device is driving to determine the output voltage range.
- Do not recommend having the external pullup or pulldown resistors. If mandatory, it is recommended the value should be larger than 50 kΩ.

0 Michael Ikwuyum over 1 year ago in reply to Atsushi Takahashi

TI__Mastermind 22315 points

Hi Atsushi,

Please see below as the internal resistors are connected to both the A and B channels. Hence, the Effects of pullup and pulldown resistors on TXS and TXB devices (Rev. A) would be applicable.

If you know the values of the pull-ups intended to be used, and if as low as 20Kohms or higher; I would further suggest TXB0304 with stronger internal pull ups, thanks.

Best Regards,

Michael.

0 Atsushi Takahashi over 1 year ago in reply to Michael Ikwuyum

Intellectual 675 points

Is my understanding of the following correct?
・Pull up/pull down are not need at both the input and output sides.
・This IC has internal 4kΩ serial resistor on I/O lines. So if it is on external pull up/pull down resistor, it is necessary to consider the effect of the voltage drop and review input level(VIH/VIL) and output level(VOH/VOL).

0 Michael Ikwuyum over 1 year ago in reply to Atsushi Takahashi

TI__Mastermind 22315 points

Hi Atsushi,

Your understanding is correct, thanks

Best Regards,

Michael.

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TXB0108: Pull-up/Pull-down of input pin