TCA9539: Can't detect Input 0.7V to be low level

Hey Nopphon,

Can you provide a schematic so we can verify the device looks okay?

"We are using a port to be input and we sent 0.7V to the port. but we got the high after we read the data from I2C.

On the datasheet, it told me that the maximum voltage input low level is 0.3 x Vcc. So it is 0.3 x 3.3 = 0.9 V.

what might be the problem?"

How are you setting the input pin to 0.7V? Are you putting a power supply to 0.7V on the pin? Are you using a resistor divider?

Anything below ~0.99V should read as a low for this device.

Do you have the polarity register set by accident? Can you verify you are reading the correct data by getting a scopeshot of the I2C read of the port?

Thanks,

-Bobby

This is the schematic.

1. We measured the voltage on the point 1 in the picture. it's is 0.7V.  Then we read it from I2C but the data on P07 is '1'.

    We got the correct data on the other ports.

    We already short the P07 to GND and the data from I2C is '0' which mean we can read the data on  P07.

2. The source which drive P07 is direct from SN74AVC2T245RSWR. We use this one to translate 1.8V to 3.3V

3. We think we set the register correct because we can read the data when we short the P07 to GND. 

Hey Nopphen,

Thanks for the image and additional information. If that is what you are seeing then I wonder if the device could be damaged.

How many boards/units are you seeing this with?

Can you test by removing the device and repopulating another TCA9539?

Can you put the removed device onto another board and retry?

Are you able to check to see what the consumption current of the device is?

Is it possible that you set the device to be an output high and then applied 0.7V at the pin?

Thanks,

-Bobby

1. We tested 2 board and the result is the same. First time, I think it might not the damaged chip problem.

    but after your answered, I think it may be possible. Because we didn't know where the factory bought it. 

2. We haven't tested by replace the chip because we didn't have the chip on hand.

    I will buy to test.

3. We haven't checked the current consumption. but it's might be 12mA which is from SN74AVC2T245RSWR at the worse case to send output 0.7V

    it's quite difficult to test the current consumption. i will do it in the last choice.

4. " Is it possible that you set the device to be an output high and then applied 0.7V at the pin? " 

    Do you mean setting TCA9539 to be output? what do you want to know? It's might damaged the chip if both are output.

Nopphon Detmaneenin said:

2. We haven't tested by replace the chip because we didn't have the chip on hand.

    I will buy to test.

Let me know what you see when you do this.

4. " Is it possible that you set the device to be an output high and then applied 0.7V at the pin? " 

    Do you mean setting TCA9539 to be output? what do you want to know? It's might damaged the chip if both are output.

I want to double check that the device is set as an input and not as an output by mistake. If you set it as an output high and SN74 drives low, it would potentially damage the device which could potentially explain why we are seeing this.

 

Also, is there anything else on pin 11 at all? I know you're saying there is an sn74 but are there any pull up/pull down resistors?

 

Thanks,

-Bobby