TXB0108: functional issue with 8-Channel TXB0108 device

The TXB requires lots of precautions; see section 8.3 of the datasheet.

There are more robust solutions if you do not need automatic direction sensing. Do you always have outputs from 5 V to 3.3 V, or would it be possible to have a separate direction signal?

Hey Sanjay,

Can you share the schematic? Are these signals unidirectional?

Hi,

        I have attached my schematics. In schematics the right hand side is a USB to DIO module which can be configured as input or output. Presently i am configuring it as output and so for any bit set at output i should get 3.3v. Also when i configure the module as input i will give 3.3v tolerant voltage at A port. 

Also one mistake i did initially was at pin 2 i gave 5vcc and pin 19 was given 3.3v. Will the device get damaged by now and perform misbehaviour.Please confirm.

Thanks

Sanjay Parelkar   

Hey Sanjay,

The schematic didn't come through correctly. As for your second question, its possible for there to be damage. I'd recommend swapping that part out just to be safe.

I need both 5v to 3.3v and vice versa. I have attached the schematics.

TXB0108 BLOCK DA]IAGRAM.pdf

Hi,

      when i make my USB4751 to 0 v (DO off) but still the output is at 3.3v and input is not 0 v but it is 5.0v. The USB4751 independently toggle from 0v to 5v and vice versa. why is it misbehaving?

Thanks

Sanjay Parelkar 

Hi,

     I have replaced the IC. Now the voltage is max 1.677v at port A(vcca= 3.3v) and injected voltage at port B is 5 vtll. If i switch off the DO bit and ON again then at one time the output goes to 3.3v else it is 1.67vdc. Why is this happping.

Thanks

Sanjay Parelkar 

usb 4751 DIO specifications attachedUSB4751 DIO specifications.pdf

Hi,

       One more observation is when i put multimeter probe at the input i.e port A then the output which was initially 1.67v is set to 3.3v. I am using this device with lenghty cable because this is my application calls for.

Thanks

Sanjay Parelkar 

You cannot use the TXB with lengthy cables (see section 8.3.3 of the datasheet).

Hey Sanjay,

As Clemens stated this device will not work well with long cables, I'd recommend shortening them. Also, the schematic you provided doesn't show much so its hard to tell if there is anything else that can be influencing this issue. Do you have any scope shots to share? Also, do the peripheral devices have the required drive strength to drive the TXB0108 I/O?

Hi,

      The length of cable is 2.5 meters. If TXB cannot be lengthy what is the other solutions, with other devices with TI. I will be driving the other device through the USB-4751 DIO module. I will try to place the device output close to the UUT around.

Thanks

Sanjay

Hi,

        what about using TXS0102 device for this application. It is having a internal pull which is tied to supply. Now the supply can source the wire.

Hi Sanjay,

Neither the TXS nor TXB devices will be able to support the length of the cable you're trying to drive. In order for us to help further, we'll need to see a more detailed schematic, and even some waveforms of what is happening at the I/Os of the translation part.

Thanks!

Chad Crosby