TCA9803: Is TCA9803 the right device to isolate a power-gated ADS1115 from an always-on I²C bus?

Sid

Part Number: TCA9803
Other Parts Discussed in Thread: ADS1115, TCA9517A, PCA9306, , SN74LVC2G66, TCA39306

Tool/software:

Hi TI team,

I’m designing an ultra-low-power sensor node (see simplified block diagram below) and need advice on the best way to disconnect one section of the bus without disturbing the rest.

Goal

Minimise system sleep current by shutting down the LDO + ADS1115 + TCA9803-B side whenever that ADC is not required.
Keep the MCU + other sensors on the always-on side communicating normally on I2C while the gated side is un-powered.

If TCA9803 is not ideal for this “hot-pluggable, one-side-off” use case, please suggest an alternative (e.g., TCA9517A, PCA9306, or dedicated load-switch + MOSFET isolation).

Thanks in advance for your help!

2 months ago

0 Sid 2 months ago

Prodigy 30 points

0 Clemens Ladisch 2 months ago

Guru 316690 points

The TCA980x can be used for such isolation.

It also acts as a buffer and level shifter. The difference between 3.4 V and 3.3 V does not matter. If you want nothing more than disconnecting a bus segment, then a plain switch like the SN74LVC2G66 would be cheaper.

0 Tyler Townsend 2 months ago

TI__Mastermind 47328 points

Hi Sid,

The TCA9803 has powered off high impedance on i2c bus pins on A-side. The use-case described should work just fine.

I agree with Clemens here. If you desire some type of switch you could use the device he recommended or try contacting the MUX team for the best solution for your application.

From my side, I can also suggest PCA9306 or TCA39306 as a simple I2C switch for separating bus segments in a system at a low cost.

Regards,

Tyler

0 Sid 2 months ago in reply to Tyler Townsend

Prodigy 30 points

Thank you. The design has 4.7kohm pull ups (each on SCA/SDA) on A side that is connected to Allways On voltage domain and the I2C sensors. When EN on TCA9803 is low, would this create any issues to the pull up values on the A side? I am assuming only the impedance of the SDAA and SCLA will be high so there is no current draw when TCA9803 is disabled. Am I correct?

0 Sid 2 months ago in reply to Clemens Ladisch

Prodigy 30 points

Thank you verry much for your suggestions.

0 Clemens Ladisch 2 months ago in reply to Sid

Guru 316690 points

Yes, when EN is low, the TCA980x has high-impedance I/Os on the A side. (The B-side current-source pull-ups are still active.)

0 Tyler Townsend 2 months ago in reply to Sid

TI__Mastermind 47328 points

Hi Sid,

Please let me know if you have any more questions.

Regards,

Tyler

Interface

Interface forum

TCA9803: Is TCA9803 the right device to isolate a power-gated ADS1115 from an always-on I²C bus?