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LMR36506: 2.2MHz and 400kHz Configuration Schematic Validation

Egemen Aksoy
Intellectual 975 points
Part Number: LMR36506


Tool/software:

Hello,

In our project we are using LMR36506 as a SMPS according to the given specs.

Vin: 5.5V - 65V, Vout: 5V, SW Frequency: 2.2MHz

The schematic is attached.

Is this schematic okay for the given specs?

Additionally, there is an other variant that shall operate at 400kHz with specs Vin: 5.5V - 65V, Vout: 5V,

For 400kHz operation schematic is attached.

Is this schematic okay for operating at 400kHz?

Best regards.

  • 0
    TI__Mastermind 31315 points

    Hi Egemen,

    For your 2.2MHz schematic, your input range cannot be that wide from 5.5V to 65V. At 65V, you are violating the minimum on-time of the device. I suggest reducing the switching frequency back to around 1MHz and increasing the inductance size accordingly.

    400kHz schematic looks fine to me. 

    In general, make sure that the saturation current of the inductor is higher than the peak current limit of the device. This is to prevent damage to the internal FET in overcurrent cases.

    Thanks,

    Richard 

  • 0 in reply to Richard Fu22
    Intellectual 975 points

    Hello Richard,

    Thanks for the reply.

    When you mentioned the device's peak current limit, did you mean this value?

    According to your reply, we decided to design for 400kHz and 1Mhz switching frequency.

    For the 1MHz, Is the schematic same with 400kHz design (except for L2)

    For the 1MHz design, 22uH inductor shall be SRN6045TA-220M

    For the 400kHz design, 47uH inductor shall be SRN6045TA-470M

    22uF capacitors shall be CL31B226KPHNNNE

    Are these inductors and capacitors suitable for operation?

    Best Regards.

  • +1 in reply to Egemen Aksoy
    TI__Mastermind 31315 points

    Hi Egemen,

    I'm referring to the high-side peak current limit, so 1.11A.

    I would add one more 22uF to account for DC voltage derating on the capacitor. Either that, or increase the voltage rating of the capacitor.

    The inductor and capacitors seem to fit well.

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Intellectual 975 points

    Hello Richard,

    I appreciate your support.

    SRN6045TA-470M Saturation current is 2A and high-side peak current limit is 1.11A.

    According to that is it safe to use SRN6045TA-470M?

    If it exceeds or is too close to the limit we can change our switching frequency to 1Mhz and we can use SRN6045TA-220M instead of 47uH one.

    Best regards.

  • +1 in reply to Egemen Aksoy
    TI__Mastermind 31315 points

    Hi Egemen,

    Yes, that's fine.

    Thanks,

    Richard