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Original question:

LM7480-Q1: LM74800-Q1 Schematic review & question

LM7480-Q1: LM74800-Q1 Schematic review

CHO SR
Genius 3415 points
Part Number: LM7480-Q1

Hi,

The customer accepted the advice and revised the schematic.

Please review the customer schematic.

OVP : 37.6V

UVLO : 19.7V

  • 0
    TI__Guru 57737 points

    Hi Cho,

    Looks like the schematic attachment is missing. Can you share it again ?

  • 0 in reply to Praveen GD
    Genius 3415 points

    Update the schematic

    1004.schematic.pdf

  • 0 in reply to CHO SR
    TI__Guru 57737 points

    Hi Cho,

    Thanks for sharing the schematics. Let me get back to you by tomorrow.

  • 0 in reply to Praveen GD
    TI__Guru 57737 points

    Hi Cho,

    Please see my schematic review comments below,

    1. The FET selected is only 40V rated. If this is an Automotive application, we would recommend using at least 75V rated FETs are recommended along with SMBJ28A and SMBJ58A connected back-back at the input. For more understanding on this topic, please refer to '11.3 TVS Selection for 24-V Battery Systems' section of the datasheet. 

    2. With 110 kohms and 6 kohms resistor ladder on the EN/UVLO pin, the EN rising threshold = 23.79V and the EN falling threshold = 21.88V

        With 110 kohms and 3.74 kohms resistor ladder on the OV pin, the OV rising threshold = 37.4V and the OV falling threshold = 34.36V

    Sorry for the delay in response. 

  • 0 in reply to Praveen GD
    Genius 3415 points

    Hi Praveen,

    Thank you for your reply.

    Please give us a guide on the calculator or calculation method for the second content.

  • +1 in reply to CHO SR
    TI__Guru 57737 points

    Hi Cho,

    It is a simple resistor divider network. So, the calculation is straight forward.

    For example, lets take EN/UVLO. There is a resistor divider from Vin to GND. R9 = 110 kohms, R10 = 6 kohms.

    To calculate the EN/UVLO rising threshold,

    Vin (R10/(R9+R10)) = 1.231 V

    Vin (6k/( 110k + 6k)) = 1.231 V

    Vin = 23.79V

    To calculate the EN/UVLO falling threshold,

    Vin (R10/(R9+R10)) = 1.132 V

    Vin (6k/( 110k + 6k)) = 1.132 V

    Vin = 21.8 V