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LM5060-Q1: Using separate Vin for driver and mosfet for LM5060 or TPS4811 or TPS2492

Tanmay Sutaria
Prodigy 155 points
Part Number: LM5060-Q1
Other Parts Discussed in Thread: LM5117, LM5060, TPS2493, CSD, CSD19536KTT

Tool/software:

Hello,

I need to add a high switch switch in the output of a variable power supply implemented using LM5117.
To drive the series N-mosfet, we can use a eFuse driver or High side driver like LM5060 or 66, TPS2493, TPS4811 etc.
No protections are required but can be used if available in the driver we finalize. Reverse flow is not required. (4811 in attached schematic, but any can be used)

The output of the switcher is required from 0.5 - 50Vdc, input is 55V from an earlier stage.
Since the driver cannot operate at that voltage, is it okay to power it from the Vin of the switcher which is 55V?

1. LM5060 or TPS4811 Vin would be 55V but mosfet drain will be at 0.5 to 50V. Will this work or cause any problems?
2. Series current will be max 20A @ 50V. Since mosfet is not switched rapidly, can we use an SMD mosfet from the CSD195xx family,
     e.g. 80V, 100A in TO-263 or is a TO-220 device recommended from dissipation requirements.
3. What is the recommended rating for Qd?

Thanks and regards,
Tanmay Sutaria.

  • 0
    TI__Guru** 105281 points

    Hi Tanmay,

    TPS4811 has good gate drive and can drive large gate capacitance/charge.

    VIN and drain of the MOSFET has to be at same potential as much as possible for all high-side drivers as the internal charge pump is driven with reference to VIN.

    Use a 5V regulator from 55VIN and do diode ORing as shown below.

    BR,

    Rakesh

  • 0 in reply to Rakesh
    Prodigy 155 points

    Hi Rakesh,

    Thanks for the revert.
    Using your suggestion, worst case condition will be 4811 Vin=4.4V and Vdrain = 0.5V.
    The mosfet should switch on / conduct in this scenario, but any additional protections required?

    Also, what is the recommended part for Qd?

    For the mosfet query(repeated below), please advise or loop in the concerned domain engineer.
    2. Series current will be max 20A @ 50V. Since mosfet is not switched rapidly, can we use an SMD mosfet from the CSD195xx family, e.g. 80V, 100A in TO-263 or is a TO-220 device recommended from dissipation requirements.

    BR,
    Tanmay.

  • 0 in reply to Tanmay Sutaria
    TI__Guru** 105281 points

    Hi Tanmay,

    When Vdrain = 0.5V, the source will be close to 0.5V. With Vin =4.4V, gate will be at 12V+4.4V = 16.4V 

    So, you can use SMD MOSFET from CSD series such as CSD19536KTT  which has 20V Vgs rating and available in D2PAK (TO-263) package.

    BR,

    Rakesh

  • 0 in reply to Rakesh
    Prodigy 155 points

    Hi Rakesh,

    Thanks for the confirmation. Will assemble, test and revert in case of any queries.

    BR,
    Tanmay.