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DS90UB947-Q1: About the communication between ds90ub947 and DS90UB948

Maksim Liu
Prodigy 160 points
Part Number: DS90UB947-Q1

Hi team,

Our customer use DS90UB947 and DS90UB948 to design a system, and the diagram as following,

Now they met some problems:
1, they can't use 3.3V even I2CSEL is floating. If they use 3.3V, the I2C bus would drop to 1V by 947 when they read register 0XC7.

if they use 1.8V to convert the 3.3V chip, I2CSEL pull up 10K, configure 1.8V mode, it is normal. Why?

2, They could read remote MCU via I2C, but can't write register(they can see the ACK signal), how to set register could realize this function?

Now the register 0xC6=0x21; 0x17=0x9E.

  • 0
    TI__Genius 10475 points
    Hello,

    The device needs to be powered up properly for the I2C to function correctly. Also confirm there is proper SDA/SCL pull-up and the IDx address and I2C configuration registers are set up properly.

    Are the 1.8V and 3.3V supplies powered up properly? If you have power supply fluctuation on the serializer side during I2C access, make sure the power supplies have settled and at proper and stable levels and then toggle PDB and then wait for a delay before I2C transaction (>1ms for local I2C access, for remote I2C wait for LOCK in addition to the PDB requirement).
  • 0
    TI__Mastermind 30515 points
    For I2C issue, please capture one plot on SCL/SDA for analysis, it is more easily to dig out the root cause. You can compare the timing relation, high/low electrical level, I2C supply voltage, pullup regsisters, etc.

    best regards,
    Steven