TXS0108E: TXS0108E - not working as expected.

Laura Moreira

Part Number: TXS0108E
Other Parts Discussed in Thread: SN74LVC8T245, , SN74AHCT541

Hello,

I'm having issues with this chip after connecting output signals are connected to the load.

This is the schematic:

This is one of the output signals (no load). The frequency is the same as the square input signal and the voltage level is 5 V as expected. Not sure why it has this small voltage drop of 300 mV.

Then when I connect the load with a 15k input impedance. This is the signal observed.

The square wave is completely distorted. The frequency is over 38 MHz.

over 4 years ago

0 Laura Moreira over 4 years ago

Prodigy 40 points

This is the schematic.

0 Dylan Hubbard over 4 years ago in reply to Laura Moreira

TI__Mastermind 43420 points

Hey Laura,

This device does not provide any drive strength (due to its passive translation architecture) of its own and does not handle heavy loads very well. I think you may benefit from a translator with buffers. It looks like the signals may all be going in the same direction so a device like the SN74LVC8T245 will work perfectly for this.

0 Laura Moreira over 4 years ago in reply to Dylan Hubbard

Prodigy 40 points

Hi Dylan,

Thank you for your reply and suggestion.

I'm just using this to translate control signals from 3.3 V to 5V. The current drawn from each output should be around 333 uA.

In the datasheet of the device TXS0108E, the maximum continuous output current is +-50 mA. This should be enough.

0 Clemens Ladisch over 4 years ago in reply to Laura Moreira

Guru 257020 points

That 50 mA value is the allowed current flowing through the closed switch, which happens only for the input at GND, and relies on the drive strength of the external device.

A current of 0.33 mA through the 10 kΩ pull-up resistor would result in a voltage drop of 3.3 V.

For unidirectional 3.3 V to 5 V translation, the simplest and cheapest solution is a buffer with TTL-compatible inputs such as the SN74AHCT541.

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TXS0108E: TXS0108E - not working as expected.