LP2986 and Schottky protection

sylvainr romion

Prodigy 30 points

Other Parts Discussed in Thread: LP2986

I have some difficulties to choose a Schottky diode to protect my LP2986.

Vin is a battery between 0V and 14.7V, I have two LP2986, one @ 3.3V and a another @ 5V.

What are the criteria for choosing my diode?

Thanks you

over 12 years ago

0 Donald Jones over 12 years ago

TI__Mastermind 22610 points

No criteria really. A general purpose Si diode could probably work as well, but the Schottky was specified to give a bit more headroom.

BAT54, or similar, is a good choice.

If both LP2986 inputs go to common connection at battery (i.e. in parallel), then BAT54-C could be used.

If the LP2986 are in series ( Vbatt > LP2986-5.0 > LP2986-3.3 >) then a diode across each device is required and BAT54-S could be used.

0 sylvainr romion over 12 years ago in reply to Donald Jones

Prodigy 30 points

OK thanks you for the reference.

My LP2986 are in parallel.

So, I apply the schematic in datasheet, but i do not understand the operation :
When Vin <Vout (abnormal operation), the diode is blocking? And when to Vin> Vout?

0 Donald Jones over 12 years ago in reply to sylvainr romion

TI__Mastermind 22610 points

When Vin < Vout (abnormal operation) the external Schottky diode is conducting (ON) and the reverse current flows through the external Schottky diode, and not through the parallel internal parasitic diode/SCR.

When Vin > Vout (normal operation) the external Schottky diode is blocking (OFF).

0 sylvainr romion over 12 years ago in reply to Donald Jones

Prodigy 30 points

Thank you for this clarification.

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LP2986 and Schottky protection