TXB0108: Is VCCB port 5V tolerant

Danilo A.

Part Number: TXB0108
Other Parts Discussed in Thread: SN74LXC8T245, SN74LVC1G34

Hi Team,

Our customer is using TXB0108 with VCCA of 1.8V and VCCB of 3.3V. Section 6.3 of the datasheet shows that the maximum voltage of VIH is VCCI. However, our customer would like to confirm if the inputs at VCCB port are 5V tolerant. If not, can they use voltage divider before VCCB port to reduce the voltage from 5V to 3.3V? If this is a possible, can you please suggest the values of the resistors for the voltage divider?

Regards,

Danilo

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 316690 points

"V_CCI" is not the same as "5 V"; the I/O pins are not 5 V tolerant.

The TXB inputs require a drive strength of at least 2 mA, i.e., the voltage divider must have a valid voltage even with that additional current.

Is the TXB actually needed? Other level shifters like the SN74LXC8T245 would be 5 V tolerant and have proper buffers. Is there actually any single signal line that is bidirectional?

0 Danilo A. over 4 years ago in reply to Clemens Ladisch

TI__Mastermind 28660 points

Hi Clemens,

Thank you for your response. The customer is using NVIDIA Jetson Nano Developer Kit and there is TXB0108 in the board where VCCA and VCCB are operating at 1.8V and 3.3V respectively.

Regards,

Danilo

0 Clemens Ladisch over 4 years ago in reply to Danilo A.

Guru 316690 points

Use 470 Ω and 1 kΩ.

This wastes lots of power; it would also be possible to convert from 5 V to 3.3 V with a buffer with overvoltage-tolerant inputs like the SN74LVC1G34.

0 Danilo A. over 4 years ago in reply to Clemens Ladisch

TI__Mastermind 28660 points

Hi Clemens,

Thank you very much for your suggestions.

Regards,

Danilo

Logic

Logic forum

TXB0108: Is VCCB port 5V tolerant