• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 48 subscribers
  • Views 705 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

THS4521 Power Down

Loc Lam
Prodigy 60 points

Other Parts Discussed in Thread: THS4521, TINA-TI

I'm testing out the THS4521 using the simulation circuit in TINA-TI.  I had the PD pin pulled low (to the ground) and the amplifier was still amplifying.  I though when the PD pin pulled low it is the same as shutting off power to the amplifier (V+ and V-) and therefore the amplifier is shut off. 

Also, if I pulled the PD pin to low (i.e. power down) but Vcc still connected to an active +5V and Vss is grounded can I still apply a larg voltage to the input pins (Vin+ and Vin-) of the amplifier?  Specifically, can I apply a sinewave with amplitude of +12Volts (i.e. swings from -12V to +12V) at the Vin+ and  a sinewave with 180 degree phase shift from the previous sinewave with amplitude of +12V to -12V to Vin- of the opamp?  Will this damage the opamp?

Thank You,

Loc

  • 0
    TI__Genius 13335 points

    Hello Loc,

    When the device is disabled (in power down mode), there is still a passive path from the input to the output. Therefore, you can see a signal at the output in power down mode.

    For the input signal, the maximum voltage that the input pins can tolerate is (Vs-) - 0.7V to (Vs+) + 0.7V as listed in the abs max table on page 2 of the THS4521 datasheet. For a 0V to 5V supply, this means the maximum voltage you can safely apply is -0.7V to 5.7V. Anything beyond this could damage the device.

    Regards,
    Luke

  • 0 in reply to Luke LaPointe
    Prodigy 60 points

    Hi Luke,

    Thank you for your answer.  I understand there is an output as there are two feedback paths between the inputs and outputs.  However, the signal at the input is 1v peak-peak and I'm getting railed outputs eventhough the PD pin is grounded.  Does the simulation circuit for this opamp in TINA simulate the function of the PD pin? 

    Thank you,

    Loc 

  • 0 in reply to Loc Lam
    TI__Genius 13335 points

    Hello Loc,

    The power down functionality seems to be working correctly.

    1452.THS4521 - Powerdown.TSC

    I tested with the reference design available on the web.

    Verify that the voltage being applied to the PD pin is less than 0.7V to ensure power down mode. If you are still experiencing issues, then you can upload your schematic and we can take a look.

    Hope this helps,
    Luke

  • 0 in reply to Luke LaPointe
    Prodigy 60 points

    Hi Luke,

    Ran your circuit and the PD pins behave as it should.  However, I still can not get my circuit to do the same.  Here is my circuit:

    0488.THS4521_PD.TSC

    Thanks,

    Loc

  • 0 in reply to Loc Lam
    TI__Genius 13335 points

    Loc,

    There are a few things I noticed.

    First, you are running your supplies at -5V to 5V (10V total), which is not a valid voltage range. The absolute maximum voltage (from Vs- to Vs+) that can be applied is 5.5V.

    Second, the logic level is listed as 0.7V above the negative rail or (Vs-) +0.7V. For a 0V to 5V system, this would be 0.7V but for a -5V to 0V system for example, this would be -4.3V or less.

    Lastly, the signal you are running is very slow and the model includes some parasitic capacitances that can be charged if ran slow enough. You can tell that the part is disabled in your simulations by looking at the slew rate. When the device is enabled, the THS4521 has a slew rate of 490V/us rising and 600V/us falling. In disabled mode, when you increase the speed of the signal you can see that the output is being charged at a rate of 173V/ms and being discharged at a rate of 100V/ms which is clearly not the amplifier.

    Let me know if there are any further questions.

    Regards,
    Luke