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Buffer with limited current output to protect the load

Saverio Ricci
Prodigy 10 points
Other Parts Discussed in Thread: LMH6321, LM334, REG1117

Dear All,

I am a university PhD student interested in designing a voltage buffer with adjustable current output compliance value.

The buffer should arrogate enough current to the load until the desired value, when the current value should remain fixed (while the voltage across the device will change of course). The load, in fact, can change drastically the resistance value (from1 Megohm to 1 kohm) and the current spike potentially destroys it.

Devices as LMH6321 have capabilities in the 10-300 mA range, but I would like something in the 10 uA to 1 mA.

There are also some references design as the SBVA011 from BURR-BROWN using REG1117 to limit current and then generic an op amp. I tried with LM334 current source (instead of REG1117) and a LTC6258IS6 low power, but it is not working.

Thank for the time you will spent for this post.

  • 0
    TI__Expert 8670 points

    Hi Saverio,

    I do have a couple of questions just to get some clarity on your design goals. Just to confirm you are looking for a device that can be configured as a buffer to drive a varying output load. If that is so there are many amplifiers that could work in this output current range of 1mA. The LMH6321 has a 10mA to 300mA programmable output current limit. Meaning the user can program the max output current limit between this range and the device can output current from 0A to that programmed limit. However, it is a fairly fast buffer and might not be needed in your design where many other slower devices could work in a standard buffer configuration. Is there any information you could provide for the bandwidth requirements of this application and any information about your input signal? Additionally, do you have a schematic of what you are working with or any sort of circuit design you can share?

    Best Regards,

    Ignacio

  • 0
    Prodigy 10 points

    Hi Ignacio,

    Thanks for your interest. To better explain what I would like, I study resistive switching memories (ReRAMs) at university. These devices instantaneously change the resistance value after a threshold voltage, passing from 1 MegOhm to some KOhm. During the swithing the current should be clamped, in order to protect the device from permanent short-circuit. For example: I apply 1 ms pulse with 2 V amplitude and the device reaches 1 KOhm. The current should be 2 mA, but I want to stop at 100 uA. In our laboratory, we use a Keysight B1500 parameter analyzer (which have a compliance current system), but I would like to substitute it with a custom circuit, which can be handled more easily with commercial microcontrollers (thus I can do more experiments).

    the instrument uses an active system, which read the current and adjust the voltage (which decreases) to keep the current at the value selected (compliance current). In the meantime of this "active system" the device can potentially be broken.

    I don't have requirements on the bandwidth, I usually use pulses with a minimum duration of 1ms. Obviously, the "clamping circuit" should be as fast as possible. Hereattached a sketch on how the IV curve should look like. 

  • +1 in reply to Saverio Ricci
    TI__Expert 8670 points

    Hi Saverio,

    Thank you for the additional information. I was able to look through our portfolio and there is not a device that has an adjustable current limit to the value you require as mentioned the best device we have with this feature has a programmable limit at 10mA minimum.  

    Best Regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    Prodigy 10 points

    Hi Ignacio,

    I agree with you :(

    Thanks a lot for the help