TXS0108E: Getting 3.3V as output instead of 5V

Abhijith Kannan

Part Number: TXS0108E

I have connected Vcca to 3.3V and Vccb to 5V. I have also connected A1 - A4 pins and OE pin to the gpio pins of a microcontroller. The microcontroller operates at 3.3V. I programmed the microcontroller to set OE pin to high and to give 500hz square wave to A1 - A4 pins. I expected B1 - B4 pins to give out the same square wave at 5V instead I got the same square wave at 3.3V. I also connected a load resistance of 50K ohm but got the same result.

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 317480 points

This should not happen. Please double-check the voltages at the supply pins, and show your board.

0 Abhijith Kannan over 2 years ago in reply to Clemens Ladisch

Prodigy 70 points

Here arduino provides 3.3V and 5V for both the dsPIC board and the TXS0108E. The dsPIC board gives a 500hz square wave to A1-A3 pins. The image below shows the output that I get currently.

0 Clemens Ladisch over 2 years ago in reply to Abhijith Kannan

Guru 317480 points

The high-level output is oscillating.

The TXS has edge accelerators that trigger when they see what looks like the beginning of a rising or falling edge. If you have ringing on the signal lines, this can falsely trigger.

Ringing is caused by the capacitance and inductance of long cables, and is probably amplified by the unstable VCC/GND voltages, also due to long cables.

This would not happen on an actual board with proper ground and power supplies. Try shorter cables, and adding decoupling capacitors near the chip.

+1 Abhijith Kannan over 2 years ago in reply to Clemens Ladisch

Prodigy 70 points

After going through several posts in the forum, I found out that setting the probe to 10x would probably resolve the problem and it did.

Logic

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TXS0108E: Getting 3.3V as output instead of 5V