TCA9539: Unable to configure a TCA9539

There is nothing obviously wrong with the schematic or the device address.

What is the voltage at the /RESET pin? Is the marking "PW539"?

Hi Karel,

I don't see anything wrong with the schematic or the data sent to the the TCA9539 via logic analyzer. Is it possible to double confirm using an oscilloscope to determine that you see the same data pattern in the logic picture? 

I don't see any discrepancies in the schematic you provided.  

Regards,

Tyler

Here is what I replied back to the email on Friday

Tyler,

I’ve verified with a scope and it looks good.  The screen capture is provided below. What is going on?

I’m trying to write to register 6.

Karel

Yes, this looks good, as far as the I²C master is concerned.

Please note that a NACK is not an answer, but the absence of an answer (the idle state of the bus is high). So it looks as if the expander does not react at all. Please check the supply voltage and the /RESET signal.

Hi Karel,

I agree with Clemens' here. The NACK does not mean that the TCA9539 is in communication with the master device. The bus is simply left idle, meaning that there is a lack of an answer from the TCA9539. 

Here is your scope annotated with the first byte.

On the 9th clock cycle, we can see that a NACK is present.

Can we double check the voltage on VCC, A1, A0, and /RESET? What is the current through ICC?

Regards,

Tyler

3.3V

all control pins are at 3.3V (ie A0,1VCC,& /RESET)

It seems to work when I add additional I2C devices to the bus.

Karel,

I don't understand how that would change anything other than add more input cap to the bus which would slow down the rising edge. Are you sure that your connections are not an issue? That something wasn't connected before, but now it is since you added an additional I2C device you may have corrected a mistake in the circuit connections? 

Also, you mentioned in the beginning of this question that you were using the TCA6416A without any issues. Just making sure that you know these are not p2p compatible although they have very similar functionality. 

Regards,

Tyler

I was using the 6416A before using this part on a breadboard using jumper wires, How are then compatible other than the address is different? 

I was just mentioning that the pins are not exactly the same. 

TCA6416A pinout: 

TCA9539 pinout:

Differences exist in the # of address pins as well as separate supply voltages for I2C and p-port side VCCI/VCCP. 

I was suggesting that maybe this difference could have been a source of the issue. The device may have been connected improperly.

Regards,

Tyler

I agree that they are not the same but if you tie a0/a1 to vcc wither chip should work, but it really does not matter since I'm not using the 6416a.

Karel,

Just double checking everything the data stream looks good, but it doesn't seem to be ACKing. You said that the TCA9539 begins to work when another slave device is added to the bus. Can you share your entire schematic? 

Regards,

Tyler

Hi Karel,

When you take scope captures, where are you measuring from? Please measure at the TCA9539 device. Double check all solder connection. Examine the differences that you make when you add another slave device to the I2C bus that causes it to work. Also, what is this slave device you are adding, do you have a part number? 

I don't see anything necessarily wrong with the schematic other than that there are not pull-up resistors present on the SDA/SCL lines. They are left as DNP. Are there pull-up resistors somewhere else in the circuit? There must be pull-ups somewhere else in the schematic since the waveform you provided shows RC like characteristics. 

Regards,

Tyler

I took the scope capture from the board using a couple soldered wires. I did add the pullups labled DNP to the board because of my configuration.