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TCA9511A: Device to isolate I2C slave from bus when powered down.

Jeff Kaiser
Prodigy 10 points
Part Number: TCA9511A
Other Parts Discussed in Thread: TCA4307, TCA9517, TCA9800

Our product uses an I2C bus from a BeagleBone Black Industrial (BBBI) to communicate with two motor speed controllers (MSC). When a motor speed controller is powered down it pulls the SDA and SCL lines low and thus kills all communication on the bus.  The I2C is running at 3.3V both on the BBBI and MSCs.  Bus speed is 100Kbits/sec but 400K is a consideration. The MSCs also have their own 10K Ohm pull up resisters but this value can be changed or eliminated.  Power to the MSC is 220 or 110 VAC.  The MSC also has a place where we can monitor a crude 17VDC (up to 10mA) to see if it is alive.

 

Looking for the best device to put at the MSC to have it go off bus if it is powered down and resume operation on the bus when it is powered up again. If required we can add circuitry to turn the 220/110VAC into a usable DC voltage to drive an enable. At this time we do not have a way to connect to the 3.3V at the MSC.

 

The application can suffer an interruption on the I2C as long as all devices can automatically recover.

 

The MSC can loose power or resume operation at any time.

 

Looking at the TCA4307 or TCA9511A as possible solutions but also open to any suggestions.  Please provide design recommendation to resolve this problem.

 

Thank you,

 

Jeff Kaiser

jk@chillirack.com

  • +1
    Guru 271360 points

    These buffers will work. You can also use translators like the TCA9800/1/2/3 or TCA9517 with VCCA = VCCB.

  • +1 in reply to Clemens Ladisch
    Prodigy 10 points

    Would any of them be preferred or more effective or are all the choices equal? Does the Hot Swap & Stuck Bus Recovery qualities of the 4307 make it a better choice in this application?

  • 0 in reply to Jeff Kaiser
    TI__Mastermind 29033 points

    Hi Jeff,

    Hot swap / hot insertion means that the device can be plugged into a live backplane from an external PCB without the need to power down the backplane first. 

    Stuck bus-recovery on the TCA4307 will automatically disconnect the bus if it detects that SDAOUT / SCLOUT are LOW for about 40ms. Once the bus is disconnected, the device will automatically generate up to 16 CLK pulses to attempt to free the bus from the device which is holding it LOW. 

    Is the idea that when MSC's lose power, the TCA devices are still powered up? Are you looking for a device that can resume I2C communication even when the I2C bus is corrupted? 

    If so, the TCA4307 and the TCA9511A would work. In case of a stuck bus, simple power cycles on I2C target devices be conducted in order to free the bus. 

    In reality, most buffered solutions from TI would work. Clemens suggested a few, TCA9800/1/2/3, TCA9517. 

    Regards,

    Tyler