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TCA9555: Application questions about the TCA9555

Lacey Lin
Intellectual 2900 points
Part Number: TCA9555

Hi team,

My customer want to use the TCA9555 to control the light-emitting diode. Below is the schematic.

The process is as below:

1. power on the TCA9555(They use the pull down register to keep the output pin as low level during power on)

2.set the register 2 and 3 t0 0.(before set the pin to output, firstly set the 0 to output port register)

3. set the register 6 and 7 to 0 to select the port as the output.(once the pin has been set as output, the level of the output is low)

So customer want to make sure during the process 1,2 and 3, the output 16 bit pin level are always 0.

Can you help to review the design and the register setting?

Another question is about the I/O status when the I2C stuck.

Customer want to know if for some reason, the communication of the I2C has been stuck, what's the status of the I/O pin. It's high level, low level or high impedance?

Lacey

Thanks a lot!

  • 0
    TI__Guru 60100 points
    Hey Lacey,

    Schematic looks good, you could move the series resistor to be to the right of the pull down resistor to avoid the voltage divider of 33 ohms and the 1k ohms when the output is high but what is currently set up is fine. (Do remember we internally have a 100k pull up so there will be a voltage divider)

    "1. power on the TCA9555(They use the pull down register to keep the output pin as low level during power on)"
    This works, the base will see a logic low upon turn on.

    "2.set the register 2 and 3 t0 0.(before set the pin to output, firstly set the 0 to output port register)"
    You are setting the output state here which is what you want to do, this is correct.

    "3. set the register 6 and 7 to 0 to select the port as the output.(once the pin has been set as output, the level of the output is low)"
    You are setting the I/O to be an output here, this is correct and matches what you want to do.

    "what's the status of the I/O pin. It's high level, low level or high impedance?"
    If the I2C bus is stuck, the I/O will be whatever the last state was previously. From anywhere in step 1 to step 3, if the I2C bus got stuck the I/O would still be logic low.

    "It's high level, low level or high impedance?"
    If step 1 and step 2 have been done, then the I/O will be an input referenced to a 100k pull up resistor.

    If step 3 has been completed then the I/O will be an output driving low. You can see the NFET in figure 23 of the datsheet that is turned on is Q2 after this step. In step 1 and 2, Q1 and Q2 are NOT turned on and only the 100k pull up resistor is providing a reference to the I/O pin.

    Thanks,
    -Bobby