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LM9036 - Decoupling / Reverse Protection Diodes required?

Alex Buergel
Prodigy 20 points
Other Parts Discussed in Thread: LM9036

I plan to use your LM9036 as a power supply for a realtime clock in an automotive control unit.

Therefore V_IN would be connected to the (filtered) vehicle battery voltage (nominal 12 V).

At the output there would be two capacitors:

1)      The 22uF capacitor as you request in the datasheet

2)      A “super capacitor” of 0.22F as the actual buffer for the real time clock

 

I have got two questions:

1)      Would there be a reverse protection diode “across” the regulator be required, connecting its output with its input? (this diode should protect your regulator in case V_IN gets removed; i.e. removal of lead-acid battery in workshop etc.)

2)      If yes: Then there would also be a “decoupling” diode required to prevent the 0.22F capacitor from being discharged, I suppose. Since this super-cap shall buffer the realtime-clock in case V_IN (i.e. vehicle battery) gets removed.

 Or are there no protection diodes required, since, in case V_IN gets removed, virtually NO current flows back into the V_OUT-pin of your regulator (and therefore the buffer-capacitor 0.22F does NOT get discharged through your regulator)?

  • 0
    TI__Prodigy 160 points

    Dear Alex,

    1) Would there be a reverse protection diode “across” the regulator be required, connecting its output with its input? (this diode should protect your regulator in case V_IN gets removed; i.e. removal of lead-acid battery in workshop etc.)

    Maybe you don't need this diode, because LM9036 already has the "−45V Reverse Transient Protection" function.

    2) If yes: Then there would also be a “decoupling” diode required to prevent the 0.22F capacitor from being discharged, I suppose. Since this super-cap shall buffer the realtime-clock in case V_IN (i.e. vehicle battery) gets removed.
    Or are there no protection diodes required, since, in case V_IN gets removed, virtually NO current flows back into the V_OUT-pin of your regulator (and therefore the buffer-capacitor 0.22F does NOT get discharged through your regulator)?

    This depends on what happens when removal of lead-acid battery happens, I mean, more likely Vin is floating at this condition, so there will be no current flow or only very small leakage current from Vout to Vin.