TINA/Spice/TXB0106: TXB0106 FOR RPI Serial Level Shifters

Andrew Buckin

Part Number: TXB0106
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

Hi All,

I have a problem. I use TXB0106 to convert RS232 3.3V from Raspberry Pi to the FTDI(USB to RS232) 5V. The output level from RPi never drops to "0" remains at the level of ~1.5 volts. I connect the FTDI 3.3V direct to RPi the output level is normal 0> 3.3V.

Thanks for any ideas

Andrew.

over 8 years ago

0 aozer over 8 years ago

TI__Mastermind 30005 points

Hello Andrew,

The only reason I could see this happening is if the load at the output of the TXB0106 is not a high impedance load. If you try to drive any load <50k ohm, you are going to start to see the Vol levels increase above 0V.

0 Andrew Buckin over 8 years ago in reply to aozer

Expert 2130 points

Thank you,

The input resistance of an FTDI is more than 50K. I increased the resistance R5 to 330R - it works. :(
With other devices works OK.

Andrew.

0 Clemens Ladisch over 8 years ago

Guru 316690 points

As far as I know, FTDI chips have TTL-compatible inputs, i.e., the RPi output signals do not need to be shifted. (Which FTDI chip are you using?)

0 Andrew Buckin over 8 years ago in reply to Clemens Ladisch

Expert 2130 points

That was my fault.

"True 5V/3.3V/2.8V/1.8V CMOS drive output
and TTL input."

Logic

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TINA/Spice/TXB0106: TXB0106 FOR RPI Serial Level Shifters