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TCA9617A: About VOL Gap. & device advice.

cyan zhou
Expert 1500 points
Part Number: TCA9617A
Other Parts Discussed in Thread: PCA9306, TCA9803, TCA9509

Hi TI Expert,

We have a problem with an I2C level conversion application, as shown in the following diagram.

PORT B of TCA9617, the output low-level voltage is 540mv, then via tca9548, PCA9306, the low-level voltage is still 540mv. Here,the I2C of PEX8796 is 1.8v interface, low level threshold is 630mv, the margin of 90mv is not enough.

We tried TCA9803 instead of TCA9617, and the PORT B of TCA9803 output low level 220mv. The low level voltage is more suitable, but there are many restrictions.

The two devices of TCA9548 and PCA9306 cannot be used together with TCA9803, and the function is not stable in the actual test.

Can you find a solution of p2p device to solve our problem?

BTW, Replace one of the TCA9617 with TCA9509, In this way, port A of TA9617 will be connected to port A of TCA9509. Is there any problem?

TCA9509 maybe not suitable for this, cause there is a description in datasheet 10.2.1 chapter.

  • 0
    TI__Guru* 77791 points

    Hey Cyan,

    "BTW, Replace one of the TCA9617 with TCA9509, In this way, port A of TA9617 will be connected to port A of TCA9509. Is there any problem?

    This should work. The device is pin to pin with TCA9617 and supports 1.8V on A side while supporting 3.3V on B side. You may want to remove the pull up resistor on A side though.

    TCA9509 maybe not suitable for this, cause there is a description in datasheet 10.2.1 chapter."

    The restriction you point out assumes you are connecting to another TCA9509 on A side. In your block diagram if you are using one TCA9617 and TCA9509 where both connect by A side, this is okay. This is our only I2C buffer which would support this though you would lose the 1MHz support (TCA9509 supports 400kHz).

     

    -Bobby

  • 0 in reply to BOBBY
    Expert 1500 points

    Hi Bobby

    I got you.

    Thanks very much.

  • 0 in reply to BOBBY
    Expert 1500 points

    Hi Bobby,

    Follow your instructions to verify the results as follows

    Port A of TCA9617 and TCA9509 is connected in parallel. The pull-up resistance is removed, and the current source of port A of TCA9509 is used to pull up.

    The high level of port A will be pulled down to 1.4v probabilistically. Is this normal? If something goes wrong, is there any way to fix it.

    According to the datasheets, port A of TCA9617 needs to be pulled up, while port A of TCA9509 has A constant current source that cannot be pulled up, which is A contradiction.

    what should we do?

  • 0 in reply to cyan zhou
    TI__Guru* 77791 points

    "The high level of port A will be pulled down to 1.4v probabilistically. Is this normal? If something goes wrong, is there any way to fix it."

    No, this is not normal. Is yellow the SCL signal and Green the SDA?

    This looks like there may be contention on the bus. Is the master on A side of the device? Is it possible the master is driving HIGH with a PFET while our device is driving low with the NFET?

    What happens when the line is idle? Does the line pull up to 1.8V?

    Can you probe the VccA on our device and make sure the power supply is at 1.8V?

    "According to the datasheets, port A of TCA9617 needs to be pulled up, while port A of TCA9509 has A constant current source that cannot be pulled up, which is A contradiction."

    TCA9509 A side is providing a pull up source so there is no need to place a pull up resistor on A side.

     

    -Bobby