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LM5146-Q1: LM5146-Q1

Anu Shetty
Prodigy 60 points
Part Number: LM5146-Q1
Other Parts Discussed in Thread: LM5146, LM25145, LM5145, CSD18563Q5A

Please review the schematic of LM5146-Q1 Buck controller,this circuit is designed as per the LM5146-Q1 design calculator tool.

The parameters i have considered for the design for 12V design are,

Vin min-16V

Vintyp-24V

Vinmax-36V

Vout-12V

Fsw-400KHz

Iout-9A

Inductor value chosen in schematic 6.8uH

and also please review the compensation design input values,according to the given input,

the cross over frequency is 56KHz and phase margin is 62 degree.

Please review the schematic and let us know your comments.

I have attched design calculator tool according with the following inputsLM5146-Q1.xlsm

  • 0
    TI__Guru 68757 points

    Hi Anu,

    This design is quite similar to the LM5146 EVM, which is 12V/8A/400kHz. Can you check what the effective capacitance of 3 x 22uF output caps is at 12VDC - this is important for loop compensation.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    TI__Guru 68757 points

    Here are some comments:

    1. 4.7uH is suitable for the buck inductor (it gives 36% ripple current, a good operating point).
    2. Cout of 50uF as entered in the quickstart is likely high (e.g. a 22uF/25V cap is < 10uF at 12VDC). Check the Murata simsurfing tool or equivalent.
    3. Consider using 60V FETs, such as the CSD18563Q5A. Take a look at the LM25145 (42V version of the LM5146) or the LM5145/-Q1 (75V version) and the applicable circuit examples in these datasheets.
    4. NC pins of the controller can be tied to GND for better heatsinking.
    5. Not shown in the schematic above but recommended is a low value cap from ILIM to GND (this is to prevent negative voltage on ILIM).
    6. L004 in the schematic ties to the SW pin, which is incorrect (it should go to the FETs).

    Regards,

    Tim