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UCC29002: LS (load share) bus maximum voltage rating when combining with TPS2412 (Power ORing)

Part Number: UCC29002
Other Parts Discussed in Thread: TPS2412

We are using the UCC29002 and TPS2412 in a load share / hot swap application. Looking into the forum this seems to be a common application.

Now I'm wondering how to deal with the LS pin maximum rating. The datasheet states -0.3V to Vdd. In a situation where only one power module is supplied the UCC29002 of the inactive power module is no longer supplied via it's Vdd pin. This is because the MOSFET connected to the TPS2412 blocks any current from the output voltage rail. I measured about 2V at the UCC29002's Vdd pin. The LS pin goes up to 5V and is violating the max rating by far. There is no internal clamping to prevent the LS pin from rising above Vdd, which is good, because otherwise the active load share controller might go into protect mode.

I'm now asking for confirmation that the maximum rating in the datasheet is incorrect and the LS pin is allowed to rise up to 6V.or even 13.5V when Vdd=0V.

  • Hi Selos,

    Max VDD in the datasheet is 15V, LS pin is allowed to rise up to max VDD(15V).

    but once LS>VDD in this case, it can not do a correct load share function.

  • According to the datasheet LS can rise up to Vdd. In my understanding this means if Vdd=0V the maximum voltage allowed at LS is also 0V. (in a situation where the device is not powered)
    I just want to double check. Can you confirm the datasheet is wrong and LS is allowed to go up to 15V independent of the Vdd voltage.

  • Hi Selos,

    that is not saying that the datasheet is wrong. As I explained LS pin can endure max VDD(15V), but this do not mean it can work normally.

    in a real application, during the situation when one module has already powered on with load and the other module still do not power on(also not VDD on the load share controller), at this moment LS voltage is higher than VDD on the module that do not power on.

    hope this is clear.