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LM5060: Driving 2 N-CH Mosfet (in back to back configuration) with LM5060 controller

Paolo Culatti
Prodigy 40 points
Part Number: LM5060
Other Parts Discussed in Thread: LM5069

Support Path: /Other topics/Design techniques and how-to guides/

Hi!

On my application there are 5 channels in parallel. Each channel is composed of one LM5060 which drives the gate of 2 N-mosfet in back to back (common source) configuration. 

During lab test, I've unfortunately realized that the overcurrent protection implemented by the LM5060 is very slow: in fact, in case of overcurrent, the N-mosfet are disabled only after 4-5ms and this causes the mosfet damage.

Could you suggest me how to fix the fault?

Thanks a lot

Paolo

  • 0
    TI__Genius 10370 points

    Hi Paolo,

    Welcome to E2E! I would like to first point out that the LM5060 does not have short circuit protection, and does not have true current limit regulation. This device is basically a high side charge pump controller with OV and UV protection. The LM5060 also does NOT have a true SOA protection (power limit) for the FET.

    If you would like short circuit protection, SOA protection for the FET, and true current limit (regulating the gate voltage), then I highly recommend the LM5069. We have a great app note discussing how to implement reverse polarity protection here: http://www.ti.com/lit/an/snva683/snva683.pdf 

    You can find it by going to www.ti.com/hotswap ==> click on “Tools & software” ==> then click on “Hot Swap design calculator tools”

    For help on filling out the excel spreadsheet, we have video tutorials. They explain how to enter the correct values cell by cell. The videos are at www.ti.com/hotswap ==> Click on “Support & Training” tab.

    I hope this helps :-)

    Best Regards,

    Aramis P. Alvarez

  • 0 in reply to Aramis P. Alvarez
    Prodigy 40 points
    Hi Aramis!
    Thanks a lot for your detailed reply!
    To be honest, the LM5060 datasheet doesn't specify all this details/limits about the overcurrent protection capability of the driver.

    The problem for me now is the pinout: the LM5060 pinout is different from LM5069 pinout and this means that i can't replace it directly on my pcb.

    In my application I have to allow the reverse polarity, in other words, the two mosfet (in back to back configuration) works like a "standard switch" (the current can flow from battery to load and viceversa).
    Is it possible to implement this feature using the LM5069?

    Using LM5069, can I use the Rdson of the Mosfet for the current measure?
    I don't need a precise current measure

    Many thanks

    Paolo
  • 0 in reply to Paolo Culatti
    TI__Genius 10370 points

    Hi Paolo,

    The LM5069 doesn't have current limit (or power limit) in the reverse direction or does not have short circuit protection on the input. The LM5069 and our hotswap controllers are mostly used for unidirectional applications. For a bi-directional current application, I would recommend some type of load switch.

    To answer your question on the Rdson measurement, the LM5069 uses a sense resistor to detect the current flowing through the FET, and it uses the voltage difference between source to drain to determine the power flowing through the FET. I hope this helps.

    Best Regards,

    Aramis P. Alvarez

  • 0 in reply to Aramis P. Alvarez
    Prodigy 40 points

    Hi Aramis, 

    many thanks for your reply.

    Here follow my comments.

    1.

    "The LM5069 doesn't have current limit (or power limit) in the reverse direction or does not have short circuit protection on the input. The LM5069 and our hotswap controllers are mostly used for unidirectional applications. "

    I don't need current limit and short circuit protection in the reverse current direction. In few words, I need current limit protection (and short circuit protection) only in one direction; in the other current direction the LM5069 shall only drive (by means the charge pump inside) the gates of the two external MOS in order to switch-on and switch-off the MOS

     

    2.

    "For a bi-directional current application, I would recommend some type of load switch"

    Every channel shall manage 50A: the load switches have current value too smaller than 50A. Am I right?

    Thanks

     

  • 0 in reply to Paolo Culatti
    TI__Genius 10370 points

    Hi Paolo,

    The LM5069 and LM5060 (as well as our hot-swap devices) have not been tested for reverse current applications (bi-directional applications). If short circuit protection and current limiting are not wanted in the reverse current model, then I think that the LM5069 could work in the reverse current application, but I'm not completely sure. I highly advise that this is tested on your prototype before manufacturing. 

    To answer your 2nd question, it's best to post this question to the load switches forum and/or check out their products at http://www.ti.com/lsds/ti/power-management/integrated-load-switches-overview.page. I hope this helps :-)

    Best Regards,

    Aramis P. Alvarez