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THS3001: THS3001 output-current & output-current-limiting protection.

user6343502
Prodigy 70 points
Part Number: THS3001
Other Parts Discussed in Thread: THS3491

When a capacitive load is connected to the output of THS3001, the output current may transiently reach about 350mA depending on the conditions (time of about 30ns).
The data sheet states that it has a current limiting function, but is it not possible to respond to the above transient operation?

Also, since the absolute maximum rating of the output current is 175mA, it is possible that a large load is momentarily applied to the device, but since the current flow time is short, there seems to be no problem in terms of allowable loss. I think.
Does the above operation cause deterioration or failure of the device?

In addition, when the current limiting function of THS3001 was confirmed by experiments, it was found that the current value exceeded the absolute maximum rating.
(The current was limited after exceeding about 180mA, and finally it was limited to about 200mA)
Is the above operation correct as the function and operation of the device?

Please see the attached file for details on the above contents and the actual waveforms.

THS3001_OCP.pdf

  • 0
    Guru 47515 points

    You should probably be using the THS3491

  • 0
    Guru 140200 points

    Hi,

    I don't understand this scheme:

    Do you mean a cable capacitance of 300pF? Is this your capacitive load?

    Kai

  • 0 in reply to kai klaas69
    Prodigy 70 points
    Hello.
    thank you for answering.
    This is a cable capacity of 300pF.
  • 0 in reply to Michael Steffes
    Prodigy 70 points
    Hello.
    thank you for answering.
    Looking at the THS3001 and THS3491 datasheets, The THS3491 allows peak currents in excess of 500mA. Since there is no similar description in THS3001, isn't peak current allowed? (Or do you not tolerate capacitive loads?)
  • 0 in reply to kai klaas69
    Guru 47515 points

    Your drawing is showing a 50ohm isolation to the cable - are you terminating in 50ohms? if so, the cable capacitance is not the way to think about it - instead, it becomes a propagation delay question and the amplifier thinks it sees only 100ohm. If it is not terminated, then yes you have a line bounce or cap load problem. 

  • 0 in reply to user6343502
    Guru 140200 points

    Hi,

    what is connected to the far end of cable? Can't you terminate the far end of cable with a 50R termination resistance? Are you using a 50R cable?

    Kai

  • 0 in reply to kai klaas69
    Prodigy 70 points

    Hello.

    The cable uses a 50Ω system, and the far end is connected to the oscilloscope.
    Its input impedance is 1MΩ.
    In addition, if it is terminated with 50Ω, it will be in the overcurrent state (10V / (50Ω + 50Ω) = 100mA) specified by the board, so it is set to 1MΩ.

  • 0 in reply to user6343502
    Guru 140200 points

    Hi,

    you could put two OPAmps in parallel as shown in figure 69 of datasheet of THS3491 :-)

    Kai

  • 0 in reply to Michael Steffes
    Prodigy 70 points

    Hello.

    The cable uses a 50Ω system, and the far end is connected to the oscilloscope.
    Its input impedance is 1MΩ.
    In addition, if it is terminated with 50Ω, it will be in the overcurrent state (10V / (50Ω + 50Ω) = 100mA) specified by the board, so it is set to 1MΩ.

    What do you think about protection against the instantaneous peak current that flows due to cable capacitance?
    (Currently, when a cable of 3m is connected, 350mA, which exceeds the absolute maximum rating of 175mA, flows about 20ns at the rising and falling edges when a square wave is input.)

    Since the above peak current has been flowing for a short time, the average power consumption due to the current is small, and the device does not generate heat abnormally.
    Therefore, I think it is unlikely to cause a device failure, but what about it?
    Also, if it leads to a failure, please tell me the conditions under which the device can be used without failure. (Output current range, etc.)

    In addition, when the current limiting function of THS3001 was confirmed by experiments, it was found that the current value exceeded the absolute maximum rating.
    (The current was limited after exceeding about 180mA, and finally it was limited to about 200mA)
    Is the above operation correct as the function and operation of the device?

  • 0 in reply to kai klaas69
    Prodigy 70 points

    Proposed Thank you.

    Will driving with one THS3001 put a strain on the device? (Does it lead to failure?)
    If it causes a failure, please tell me the conditions under which the device can be used without failure.
    (Output range that can guarantee device operation of DC output current and instantaneous output current, etc.)

  • 0 in reply to user6343502
    Guru 140200 points

    Hi,

    in any case, the maximum output current or 175mA specified in the absolute maximum ratings must not exceeded, not even very briefly.

    So you can either put two or more THS3001 in parallel or you could take the THS3491, as already recommended by Michael, which can a much higher output current, 520mA versus 120mA :-)

    Kai

  • 0 in reply to kai klaas69
    Prodigy 70 points

    thank you for answering.

    Consider in the suggested way.

    If you have any concerns, I may ask you another question.