TXS0108E: Noise coupling in output signals

Ankit Gupta6

Part Number: TXS0108E
Other Parts Discussed in Thread: TXB0108, LSF0108

Hello,

I am using TXS0108E as a PWM buffer ic between DSP and an isolated gate driver.

I am facing problems with the noise coupling.

The figure attached below shows a signal at the input of the gate driver. The trace length between TXS0108E and the gate driver is about 10 inches.

We can observe voltage peaks at the turn-on and turn-off, I assume that these might be caused by the one shot triggering circuit inside the IC.

However, as can be seen in the un-zoomed portion of the figure, noise can be seen in places where the signal should normally be high. The noise looks something like this

Can this be the noise induced by the sharp rise time of other PWM signals passed through TXS0108E?

Is there any alternate IC that i can use as a bi-directional level transition buffer ic, which is Pin compatible with TXS0108E?

Thanks for help

Ankit

over 5 years ago

0 Clemens Ladisch over 5 years ago

Guru 317260 points

The one-shot will trigger when it detects what looks like the beginning of an edge, so it will be affected by noise.

There is not pin-compatible replacement. The TXB0108 also has one-shot triggers, and the LSF0108 has a different pinout and requires external pullups.

0 Ankit Gupta6 over 5 years ago in reply to Clemens Ladisch

Intellectual 565 points

Hello Clemens;

Thank you for the reply.

I checked the input to the TXS0108E, the input lines look clean without any noise. The noise coupling is observed at the output, as if there is an internal coupling between the signals.

I observed that i have a 10kohm pull down resistor at the output of TXS IC which is causing the spike in the output. I will try to replace it with a 100kohm pull down resistor and see if the noise goes down.

Can you please let me know of any other debugging step that can be used to resolve this problem?

Thank you

Ankit

0 Clemens Ladisch over 5 years ago in reply to Ankit Gupta6

Guru 317260 points

The TXS has internal pull-up resistors; you must not use pull-down resistors with it.

0 Ankit Gupta6 over 5 years ago in reply to Clemens Ladisch

Intellectual 565 points

The main reason to put a pulldown resistor is that, when the OE pin is pulled low the output goes in a high impedance state. I need to make sure that in such conditions the input to the gate driver pin is low.

Can you suggest any other way to achieve that?

0 Clemens Ladisch over 5 years ago in reply to Ankit Gupta6

Guru 317260 points

This is not possible with the TXS.

Do all eight channels go in the same direction? What are the two voltages?

0 Ankit Gupta6 over 5 years ago in reply to Clemens Ladisch

Intellectual 565 points

In my application i require bi-directional capability.

on A side i have 3.3 V and on B side i have 5 V.

0 Clemens Ladisch over 5 years ago in reply to Ankit Gupta6

Guru 317260 points

Gate driver inputs are not bidirectional. Is there any single signal that is bidirectional? How many unidirectional signals are there in each direction?

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TXS0108E: Noise coupling in output signals