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Hello,
I would like to reset / power-cycle several I2C devices (LDC1614) connected to TCA9548A channels, in case of a rare,
otherwise unrecoverable IC2 bus problem.
My hardware-setup:
- TCA9548A powered by a DC-DC converter out 5VDC, together with I2C master.
- TCA9548A secondary side pull-ups powered by a DC-DC converter 3.3VDC.
The latter DC-DC converter is also powering all LDC1614 devices on the board. It has an enable input connect
to MCU board (running from the 5VDC power supply)
Though the provision is there to power-cycle (reset) all I2C devices, meanwhile I have some doubts if it is really save to do so.
After all, during such reset action the TCA9548A would be still powered-on, but the pull-up on the mux channels would see 0VDC
because the 3.3VDC converter would be disabled for short period of time.
Regards,
Jo
This device is a passive switch; no current will flow from the TCA's VCC into any output.
However, if any channels are enabled, current can flow through the 5 V pull-up resistors to the unpowered side. So you should reset the TCA at the same time.
With a 5 V supply, the TCA might show up to 3.5 V at the outputs (see figure 14). Consider moving the TCA to the 3.3 V supply.
I must level-shift the reset input of TCA9548A, right ? ( unless changing MCU pwr to 3.3V as well)
Or allowing only sink and Hi-Z on the MCU I/0 pin, then no need for level-shifting
Yes; the /RESET pin is not overvoltage tolerant.
Using an open-drain signal with a pullup to 3.3 V is a level shifter. :-)
Clemens,
Thank you- TCA9548A now powered from VDD domain of I2C devices (3.3VDC)