TS3A5018: Is there any internal pull up in MUX?

Helen Lin

Prodigy 100 points

Part Number: TS3A5018

Hi TI team,

We found that there is something internal pull low when we select the channel.

Please refer the diagram as below, there are 2 cascaded mux switches in the path of our each device.

We set the latter in NO channel.
We set the former in NC channel, and control by a GPIO cmd.

Please refer our test waveform.

When the channel switching from NC to NO. The signal of NC channel will release high voltage.

Is there any internal pull up in MUX? Thanks.

BR,

Helen

over 1 year ago

0 Helen Lin over 1 year ago

Prodigy 100 points

Sorry for my typo,

I want to check whether any internal pull low in the MUX. Thanks.

0 Clemens Ladisch over 1 year ago in reply to Helen Lin

Guru 244370 points

An analog switch is passive; it behaves like a small resistor. There are no pull-ups or pull-downs.

An open switch does not have any voltage. It is likely that the input impedance of the oscilloscope acts as a pull-down.

0 Helen Lin over 1 year ago in reply to Clemens Ladisch

Prodigy 100 points

Hi Clemens,

But we've already pull up in the MUX both output and input.

I don't think probe with this ability to drive low....

0 Clemens Ladisch over 1 year ago in reply to Helen Lin

Guru 244370 points

The diagram does not show any pull-up resistors. I guess those lines to VCC are resistors (and the other lines are not)?

At which points are you measuring MXIC and MRP?

0 Helen Lin over 1 year ago in reply to Clemens Ladisch

Prodigy 100 points

Hi Clemens,

There are pull-up resistors at both input side and output.

Measuring the device pin of MXIC and MRP.

+1 Clemens Ladisch over 1 year ago in reply to Helen Lin

Guru 244370 points

MXIC is connected to the master. The master pulls the line down.

+1 Rami Mooti1 over 1 year ago in reply to Helen Lin

TI__Mastermind 23853 points

Hey Helen,

There aren't any pull up or pull downs from the mux. As Clemens mentioned here, the mux is a passive device which will just act as a RC but won't redrive or pullup/down any signal. If you want to confirm this you could remove the muxes and replace them with passive components (aka resistors and caps if you wanted as well). You could also try isolating just the control and peripherals and seeing where the pulldown is happening.

Thanks,
Rami