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LM66100: Reverse polarity protection for series-parallel AA batteries

Abdelhakim ERRAOUI
Prodigy 80 points
Part Number: LM66100
Other Parts Discussed in Thread: LM74610-Q1, TPS2121

Hi,

I have tow identical power supplies sharing the same load and are supposed to work at the same time. Each one is done by 3 AA 1.5 batteries in series (3.6V to 5.4V operating range).

So, I am locking for a solution that can protect the board and the batteries in the following cases :

  1. When both supplies are wrongly inserted
  2. When only one supply is wrongly inserted and the other is not

I found the LM74610 and LM66100 which I can use for my purpose. I think LM66100 is suitable for my application for its cost efficiency, minimal design and power consumption (quiescent current is less than 1µA in normal conditions).

I can use it this way :

But I'm not sure about two things

One is the pulse/peak current that this switch can provide :

I see in the datasheet page 4 in 6.1 section : Maximum Pulsed Switch Current (≤120 ms, 2% Duty Cycle) : 2.5A
While, my board can have current bursts of 2A due to a cellular module in GPRS mode. The pulse width is 611µs every 4.6ms
I don't know if this is critical for my application's current specs.

The other is that Vin1 and Vin2 are the same :

In normal operation, will both LM66100 be ON or just one ? How the setup above can deal with two identical power levels ?

Is there any other things I should take into consideration ?

Would this solution work ?

Thanks,

  • 0
    TI__Genius 10652 points

    Abdelhakim ERRAOUI said:

    In normal operation, will both LM66100 be ON or just one ? How the setup above can deal with two identical power levels ?

    Abdelhakim ERRAOUI said:
    I see in the datasheet page 4 in 6.1 section : Maximum Pulsed Switch Current (≤120 ms, 2% Duty Cycle) : 2.5A
    While, my board can have current bursts of 2A due to a cellular module in GPRS mode. The pulse width is 611µs every 4.6ms
    I don't know if this is critical for my application's current specs.

    This can be an issue, this is roughly 13% duty cycle. Please check junction temperature at your ambient temp. You may need to select an uprated device or one with external controller. The 2A can be handled by the switch but the duty cycle is the concern for heat. 

    Abdelhakim ERRAOUI said:

    In normal operation, will both LM66100 be ON or just one ? How the setup above can deal with two identical power levels ?

    Only One can be on in normal operation as the comparators have hysteresis, see the different between Von/Voff. 

    If both voltages are equal, it will depend on which comes online first  

    Please let me know any further questions on this, 

    Best

    Dimitri

  • 0 in reply to dimitri james
    Prodigy 80 points

    Hi,

    Thanks. Your answers were very helpful

    Actually the GSM module is ON 20 times (MAX) a day for 40 seconds approximately. I think it can be critical for the LM66100

    I am thinking about the LM74610-Q1 which can drive an external NFET and thus can handle the 2 Amps bursts or more.

    By using it in this configuration :

    If I understand correctly the functioning :

    At startup PS1 and PS2 are equal, so the output will take the first supply plugged in.

    Lets say PS1 is the supply that came in first :

    So when PS1 drops and PS1 becomes less than PS2. the device switches to PS2 and vice versa until the two supplies drop to "0V"

    Is it correct ?

    And is there any drawbacks or risks of this configuration ?

    Thanks in advance,

    Abdel

  • 0 in reply to Abdelhakim ERRAOUI
    TI__Genius 10652 points

    Adbel,

    Have you considered a PMUX such as TPS2121 which can handle this current? it has a back-to-back configuration, as well as adjustable prioritization/switchover of one voltage. 

    You can ensure the mux is OFF when you dont need it by driving OV1/OV2 pins HIGH (>1.07V), and pull them low to turn it on. 

  • 0 in reply to dimitri james
    Prodigy 80 points

    Hi Dimitri,

    Yes, I have considered using a power MUX like TPS212x devices.

    But the issue is the current consumption of these ICs. In fact, the Iq is about 200µA for each input, which is too high for my application battery life. Actually my board still in low power mode for almost 90% of time consuming about 20µA.

    Abdel,

  • 0 in reply to Abdelhakim ERRAOUI
    TI__Genius 10652 points

    Understand on the current consumption issue. 

    The voltages being exactly equal is very unlikely. Since both battery banks are equal, is there a certain battery bank which you would like to prioritize, even if its voltage is lower than the other?

    If you don't need to prioritize one pack over the other then there is no issues with your configuration. 

    Best

    Dimitri