Hi - looking for some advice on how to get around a problem I see when the Teensy 3.5 is off. My project is set up as a teensy acting as an i2c slave hanging off a cable from the master (which is also a Teensy 3.5). The i2c bus is shared among several other devices. The slave has 2.2kOhm pullups to the Master's VCC of +5V (which also comes down the cable). The slave Teensy, however, is powered off a different 5V supply than the master. The slave Teensy has the USB power line cut so it can be externally powered.
When the Teensy slave's 5V supply is ON, all the communications work well, including communications to other i2c devices. The rise time of the clock and data lines look good so the pullups seem right. However, when the Teensy slave's 5V supply is off, it drags down the i2c bus to about 400mV. It seems almost like it is trying to draw power from the lines or something. When it's in this state, no other i2c device can communicate with the master since the bus is being dragged down.
I'm sure an i2c buffer chip would prevent this but I'm wondering whether there are any simpler solutions available, since kludging a chip onto my slave board won't be very pretty. Does anyone have recommendations?
TIA
Best,
Dennis
When the Teensy slave's 5V supply is ON, all the communications work well, including communications to other i2c devices. The rise time of the clock and data lines look good so the pullups seem right. However, when the Teensy slave's 5V supply is off, it drags down the i2c bus to about 400mV. It seems almost like it is trying to draw power from the lines or something. When it's in this state, no other i2c device can communicate with the master since the bus is being dragged down.
I'm sure an i2c buffer chip would prevent this but I'm wondering whether there are any simpler solutions available, since kludging a chip onto my slave board won't be very pretty. Does anyone have recommendations?
TIA
Best,
Dennis