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Reverse Battery Protection for the LP3996

Other Parts Discussed in Thread: LP3996

Hi, so I am interested in using the LP3996, which is a dual output LDO regulator. I am wondering about how to do reverse battery protection though, as the datasheet doesn't say anything about that.

The device has EN pins which shut the device down when they are pulled low. If I tie both EN pins to VDD, will this provide reverse battery protection, or will the device be destroyed? I am planning to use a single cell Li-ion battery, so the reverse voltage is up to about 4.4V.

The datasheet is here: http://www.ti.com/lit/ds/symlink/lp3996.pdf

  •  "... If I tie both EN pins to VDD, will this provide reverse battery protection ..."

    No, this will not provide any protection against reverse battery.

    Not knowing any details, it may be possible to add reverse protection with a single schottky diode in series with the battery. This will reduce the voltage at the input of the LP3996, so this might not be appropriate is either of the outputs are at 3.3V.

    Using a MOSFET can reduce the voltage drop, but attention must be paid to Vgs when selecting the MOSFET.

    See the application note: SLVA139: Reverse Current/Battery Protection Circuits

    http://www.ti.com/lit/an/slva139/slva139.pdf

     

     

  • Yeah, I've been doing it with MOSFETs in the past, since the schottky would create a low voltage problem. My main reason for asking is that I'm building a device with very limited pcb space, so I'm trying to keep the number of ICs/components to a minimum.

    My application is pretty standard. The regulator takes the Li-ion battery and outputs 3.0V and 3.3V. The 3.3V powers some op-amps, the 3.0V powers a PIC microcontroller. The system as a whole only uses about 1mA, it's very low power.

  • That leaves the battery interface (i.e. connector) to not allow a reverse battery connection to be possible.