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ADM1270 transient protecion

On the ADM1270 evaluation board I am testing the protection for Vin min = 48V, Vin max = 56V. Is it good enough protection for IC if I solder SMAJ58CA on TVS D1 sites.

  • Hi Davorkot,

        The ADM1270 can withstand an absolute maximum voltage up to 66V. The FDS9958 FET on the eval board can only withstand 60V. Your SMAJ58CA may not break down until 71.2V, which could damage both the ADM1270 and the FET. I suggest that you choose the SMAJ54CA instead. This will break down between 60 and 66V, which is a compromise between your maximum operating voltage and the max breakdown protecting the other devices on the board.



  • Can you advise me which circuit to use for transient and reverse polarity protection? It must have fault or power good output and UV, OV and OC protection. The input voltage is 48V to 56V for my stepper motor driver (12A). My circuit with the ADM1270 using P-Channel MOSFETS is heating up a lot. I would really like to have a hint which circuit would be appropriate

  • Hi Davorkot,

        The ADM1270 is a good device to for your application. The heating problem that you are encountering is with the FET. If you are using the eval board with the installed FET, then you will see that it has about 100mR of resistance. It cannot sustain 12A for any length of time. Remember that self heating is proportional to R * I^2, so you need a FET with lower Rdson.

        You should replace that small FET with another one more suited to carrying 12A. Notice on the back side of the eval board are some FET footprints for DPAK and D2PAK devices. You can remove the FDS9958 from the board and solder down a pair of RSJ250P10FRATL, or STD25NF10LA.

        You can try using 2 FETs in parallel, which will reduce the current flowing through each FET by about half and thus cut the self heating by a factor of 4. The difficulty with parallel FETs is only in the eval board itself, which is not configured for parallel devices, and will require reconfiguration. You can make your own board, of course, and place more FETs in parallel.