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LM2940 protection diode, output capacitor

Adam Dudek
Prodigy 10 points

In my new design i will use the LM2940 (+5V and +15V version). Could you tell me if i
must use a protection diode between input and output of the LM2940 (when i have large capacitive loads)
or the protection diode is generally not needed (LM2940 has protection diode inside) ?

In which frequency i have to test my capacitors for the ESR values to match
the values in the datasheet of the LM2940?

  • 0
    TI__Mastermind 22610 points

    " ... must use a protection diode between input and output ..."

    Depends on what you define as "...large capacitive loads ..." , and how Vin behaves at power-down.

    There is no internal diode specifically for reverse voltage/current protection.

    Generally, the external diode is not needed. However, if your output capacitance is unusually large (>470uF), or if Vin gets quickly discharged down to 0V at power-down, then the I would recommend the diode be used.

    My general recommendation is : If in doubt, add it.

    As for ESR test frequency, generally anywhere in the range of 10kHz to 100kHz is adequate.