• TI Thinks Resolved

TS5A23159 Ringing?

Hello,

     Looking forward to your help in sorting out this issue. 

The objective is to switch between an analog voltage and ground at high switching speeds with reasonable current drive capability (about 20-30mA). 

The signal sequence is as follows: a microcontroller generates the analog voltage (needs to be software configurable and hence the uC). The uC output is connected to one input of a TS5A23159 analog SPDT, the other input being shorted to ground. The output of the switch is connected to a high speed opamp OP4830 configured in unity gain mode. 

The problem is as follows: The output rings as the switch transistions from ground to analog voltage. Following is the oscilloscope screenshot

The output has to transition from 0 to ~3.5V when this happens. Further, the ringing does not end in the output settling to 3.5V there is some sort of capacitor charging behavior following up.

Following is the screenshot (zoomed out and a larger time frame)

  

The above measurements are with no-load at the output of the opamp. 

Please advise on the following:

1) How to reduce the ringing

2) The output has to rise from 0 to 1V in less than 200ns (the switching speeds of the chain components add up to this number). 

What could be the reason for such a response?

Thank you for your time in looking into my case,

  • In reply to SM:

    SM,

    I wanted to give you an update of my status.  I have received the TS5A23159 ICs and mounting hardware.  I have sent these off to be assembled and should expect them back in a couple days. 

    Thank you,

    Adam

  • In reply to Adam Torma:

    Hello Adam,

               Any update on the tests with the switches?

    Regards,

    SM

  • In reply to SM:

    SM,

    I have the boards back and can now start building your test set up.

    In the schematic it looks like you have a potentiometer for R6. What type of potentiometer is it and what is the resistance value.

    Thank you,
    Adam
  • In reply to SM:

    Hello Adam,

             May I ask if you have any update for us.

    Regards,

  • In reply to SM:

    I'm sorry SM I didn't hear from you on my previous post and I put your issue aside thinking you had solved your issue. I am not able to get in the lab this week due to holiday travel but if you still want me to show you the TS5A23159 device switching from 0V to 5V without delay I can do that next week.

    Again I'm sorry for putting your thread aside as I thought you had gotten what you needed.

    Adam
  • In reply to Adam Torma:

    Hello Adam,
    The pot is a regular Bourns 20K pot. Yes, we definitely need your help.
    Regards,
  • In reply to SM:

    SM,

    I have been able to duplicate your delay in the lab using only the TS5A23159 configured the way you have it in your schematic using a 20k ohm resistor for your potentiometer.   The yellow wave form is the IN1 signal and the blue waveform is the COM1 pin. 

     .

    I removed the 20k ohm resistor between the 5V supply and pin2 NO1 and saw no delay

    This lead me to think that there is an RC delay created with resistor and the TS5A23159 On-state capacitance.  The on-state capacitance of the TS3A23159 is ~56pF.  With the 20k ohm resistor I would expect to see a ~1.12us delay for node to reach 3.15V which is what I measured below.

    To reduce this delay you could use a lower resistance or a different switch with lower on-state capacitance so it doesn't take as long to charge up the node when the signal path is selected.  On the TI.com switch selection tool you can filter some devices on their on state capacitance spec.

    I'm sorry for the delay on responding to this.  Let me know if this helps. 

    Adam

  • In reply to Adam Torma:

    Hello, Adam.

    I want to know whether TS5A23159 can be applied the case that the switch frequency is 5MHz ?

    I found the output of the chip  appeared signal distortion under such high switch speed.

    The yellow waveform is the IN1 (Pin 1), the blue  waveform is the NC (through 400Ω to ground). And the COM is connected to 2VDC.

    Looking forward to your reply, thank you.

    Debao Wei

  • In reply to debao wei:

    Debao,

    The yellow signal into pin 1 (IN) needs to be larger voltage amplitude inorder to cross the valid logic high threshold (Vih).  Based on your scale in the scope shot of 200mV it looks like your signal is only going up to 400mV which is not enough to make the IC switch the COM pin from the NC path to the NO path.  If your Vcc is 1.95 V you need at least 1.5 V on the IN pin to switch the COM pin from NC to NO. 

    What you are seeing in the blue wave form is likely the parasitic feedthrough from IN pin. 

    We don't specifically spec the max switching frequency but we have the Ton and Toff times which can give you an idea how fast you can toggle between the channels.   The TS5A23159 should be able to handle ~10 MHz. 

    Here is a like to an article that explains a little bit more about the Rule of Thumb #1: Bandwidth of a signal from its rise time

    Thank you,

    Adam

  • In reply to Adam Torma:

    Adam, thank you for timely reply.

    In fact, the voltage amplitude of yellow signal into pin 1 (IN)  is large enough, because the voltage has a X10 attenuation when we use a oscilloscope probe.

    The following figure is the right waveform. So I still want to know whether the poor signal quality of IN bring the signal distortion of NC. 

    Thank you.

    Debao

    oscilloscope probe