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PCA9534: Sporadic bus contention observed on PCA9534

Peter Guan
Prodigy 90 points
Part Number: PCA9534
Other Parts Discussed in Thread: , TS3USB30

Hello

We are seeing some sporadic bus contention on a design with the PCA9534. See the attached scope capture.

  • The design is using the Beaglebone as the I2C master, and have 8x PCA9534 as digital input on the bus.
  • Our process for everyread cycle is:
    • Write 0xFF to reg 0x03 to set all ports to INPUT.
    • Write 0x00 to reg 0x02 to set default polarity.
    • Read reg 0x00 for input logic.
  • This can happen at anytime, on a write to any of the PCA9534. 
  • This is the 3rd board revision with a fairly recent SMT build. We never had this kind of issue on the previous revisions.

Any insights would be welcomed. Thank you.

Peter

  • 0
    TI__Mastermind 21145 points
    Hello Peter,
    What else is on the bus and what are their addresses? These are some weird waveforms. Can I also look at schematics to see if everything looks ok?
    -Francis Houde
  • 0 in reply to fhoude
    Prodigy 90 points

    Hello Francis

    Here's the address table:

    Part Number Count Address Note
    PCA9534 8 0x20 to 0x27
    PCA9534A 3 0x38, 0x3A, 0x3C
    24AA02 8 0x50 This device is decoupled from the bus during normal operation by TS3USB30 switch

    Here are the schematic, there are 1.5k pull up on the bus shared by all the slave devices which are not shown on the schematic. 

    1. 8 x PCA9534. This is where the errors are occurred. The local bus is “I2C_1.SCL/SDA” is the same bus as the JIG_SCL/SDA in other schematics. The local bus “I2C_2.SCL/SDA” is on a different I2C bus. This design is repeated 8 times, and we use variant (BOM) to set the proper address to each. 

    2. 3 x PCA9534A. We have no error returned by software from these devices.

    3. 8 x 24AA02. This design is also repeated 8 times. The default state is having DUT_SCL/SDA switched to EEP_SCL/SDA. The JIG_SCL/SDA is decoupled from the EEPROM during normal operation. We confirmed that this is the case when the error on JIG_SCL_SDA happened. 

    Thanks,

    Peter