TXB0104-Q1: TXB0104-Q1 in series, is it possible?

Damiano Balzani

Prodigy 200 points

Part Number: TXB0104-Q1
Other Parts Discussed in Thread: SN74LVC2T45-Q1

Dear all,

i need to connect 2 different boards by a 40cm long cable. The communication interface is SPI.

Inside the board the voltage level is 3V3 and for transmission 5V is used.

I wonder if is it possible to connect two TXB0104-Q1 in series as reported in the image attached:

Thanks for your support

Damiano

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 243820 points

This is not possible; a TXB output does not meet the drive strength requirements of a TXB input. (Neither would a TXB output be able to easily drive a 40 cm cable.)

You need translators with proper output buffers, such as the SN74LVC2T45-Q1. (There is no single 5 V SPI translator; you have to implement the 3+1 signals in different directions with multiple devices on each side.)

0 Damiano Balzani over 4 years ago in reply to Clemens Ladisch

Prodigy 200 points

Hi,

Thanks for your work.

"Neither would a TXB output be able to easily drive a 40 cm cable"

How you can understand that? is the low output current ?

thanks

0 Clemens Ladisch over 4 years ago in reply to Damiano Balzani

Guru 243820 points

Yes, both the low DC output current, and the short time of the edge accelerators (designed for loads < 70 pF).

0 Damiano Balzani over 4 years ago in reply to Clemens Ladisch

Prodigy 200 points

Thanks for your willingness.

What is the best way to calculate the cable capacitance?

For example I'm using a cable made of some single wires

0 Clemens Ladisch over 4 years ago in reply to Damiano Balzani

Guru 243820 points

The are cable capacitance calculators on the internet, but with the trace and connector capacitance, it might be a better idea to just look at the waveform.

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TXB0104-Q1: TXB0104-Q1 in series, is it possible?