This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TS5A23159 Ringing?

Expert 1730 points
Other Parts Discussed in Thread: TS5A23159

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,

  • P.S. By no load I mean other than the scope.
  • Following is the schematic

  • Hello,

            The ringing problem has been solved (in a certain sense). The ringing was being caused due to the oscilloscope probe. Adding a series resistor around 5K (to the tip of the oscilloscope probe) stopped the ringing completely (but also made the rising edge less sharp). 

    However the ~10us capacitive charge like waveform in the transition from zero to high voltage still persists. Please advise. 

    The slew rate of the opamp used is 560V/us so that should not be the cause. 

  • SM,

    To help debug the TS5A23159 can we take a look at the scope shots of the COM1, NC1, NO1, and IN1 on one screen so we can see if there is is an issue with input and output of the switch during switching?

    Thank you,
    Adam
  • Hello Adam,

             Thank you for your reply and time. 

    The yellow waveform is the input at the NO port and the blue waveform is at COM (note the difference in voltage scales). 

    We also tried the alternate approach of using the trimpot to feed the voltage at the NO port (please refer to the schematic). The behavior is same but the delay is much less now. Following is a picture of the waveforms,

    Looking forward to your input,

    SM

  • SM,

    The wave forms look good from a switch perspective.  The switch is passing the input to the output with no distortion.  We will need to look elsewhere in the circuit for your extra loading. It appears the when you switch to the NO path that your power supply is getting loaded and cant immediately drive the input to the op amp.  I'm going to move this thread to the op amp forum for more assistance on that part of your circuit.  

    Thank you,

    Adam

  • SM,

      Can you please post a screenshot of the opamp output after adding the series 5kOhm so I can see what we are dealing with. The reason you are seeing a slow rise time is because the 5kohm series resistor along with the probe capacitance forms a low pass filter which will slow down the edge rise/fall time.

    Also, can you configure the amplifier in a gain of 2 (6dB). If you look at figure 2 you will notice that in unity gain config, there is 5-6dB of peaking in the frequency response. This indicates insufficient phase margin and can lead to ringing and other stability issues.

    Please do a before and after screenshot so I can see what issues were resolved with these 2 fixes.

    Finally what is the output impedance of the uC analog output?

  • Hello Adam,

                   We disconnected the op-amp from the path and the ouput is still the same so I am quite sure that the problem is with the switching circuit. Again, we have tried both the potentiometer and the microcontroller's DAC as sources of voltage and in both cases there is a drop at the output; the only difference being the time required to recover. 

    SM

  • SM,

    Thank you for trying additional debug steps. If the only parts in your circuit are power supplies and the switch you may have uncovered something we haven't seen before. Have you tried other TS5A23159 ICs and they see the same behavior?

    I have ordered some samples of the this device so I can try and bread board your circuit to see if I can see the same slow rise time when switching from NC to NO. Devices take 1-2 days to show up on my desk and will need another day to solder the parts down on some boards. I should have some scope shots for you by the end of next week.

    Thank you,
    Adam
  • Hello Adam,

                Yes, the circuit now is only the switch and power supply.

    Looking forward to your inputs.

    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

  • Hello Adam,

               Any update on the tests with the switches?

    Regards,

    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
  • Hello Adam,

             May I ask if you have any update for us.

    Regards,

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

  • 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

  • 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

  • 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

  • Debao,

    Would you be able to show the IN pin (1), NC 1 pin (9), COM1 pin (10), and NO1 pin (2) on one screen? 

    Something is not correct based on your description above and the scope shot.  Below is a picture of how I understand your circuit and the expected waveform relationship between IN1 and NC1.  When the IN1 pin is low that COM pin 2V should be present on the NC1 pin.  When the IN1 pin is high the NC1 pin should be pulled down to ground.  The waveforms you are showing are the opposite.  Would you please help confirm my understanding of your circuit?

    Thank you,

    Adam