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LM74500-Q1: Design Guidelines - and failure modes

richard Johnson
Prodigy 50 points
Part Number: LM74500-Q1

We have this design:

100A Input, 12V

Is there anything in the design we should be concerned about?

We are worried about a failure in the charge pump causing higher impedance across the fets (fet body diodes). Is there a way could monitor the driver for failure and fault safely? 

  • 0
    TI__Guru 57737 points

    Hi Richard,

    The schematics look okay to me except for the FET Vds rating. The TPHR9003NL seems to be 30V rated FET. 

    Is your input a 12V automotive battery ? Also what is the input TVS part number ?

  • 0 in reply to Praveen GD
    Prodigy 50 points

    It is, what are your thoughts? Bulk capacitance on the output ok? TVS: 5.0SMDJ26CA

  • 0 in reply to richard Johnson
    TI__Guru 57737 points

    Hi Richard,

    Circuits connected to12V automotive batter can be subjected to transient voltages as defined by ISO 7637-2 and ISO 16750-2. To withstand these transient pulses, you will have to use either

    1. A 60V rated FET with a single bi-directional TVS like SMBJ33CA. For more understanding , please refer to datasheet section '9.3.1.3 Selection of TVS Diodes for 12-V Battery Protection Applications'  or
    2. A 40V rated FET with two uni-directional TVS connected in back-to-back configuration as shown below. For more understanding on TVS selection while using 40V rated FETs, please refer to section ‘10.2 TVS Selection for 12-V Battery Systems’ of LM74810-Q1 Datasheet.