Choosing the right load switch for battery hysteresis

Paul Kilcoyne

Other Parts Discussed in Thread: TPS22930A, LMP7300

Hi there,

first time poster. I've been advised that I need a load switch with under voltage cut off and hysteresis so that I can cut the connection to my load from the battery when battery voltage becomes too low and then reconnect the load when battery voltage has been charged to a higher/safer voltage.

Here are my details;

Solar MPPT controller charging battery and load connected in parallel, at night load drains battery, during daylight solar MPPT charge controller charges both battery and load.

I'd like some circuitry to control the connection from battery to load, during daylight allow load to be connected but when no voltage/current from MPPT and battery voltage drops to 2.8v cut off the load.

When battery gets charged up to say 4.0v allow load to be reconnected to circuit.

Is this possible with a TI product, can someone advise how this can be achieved?

Attached is a photo of set up I'd like to achieve.

Thanks,

Paul

over 6 years ago

0 Ed Walker over 6 years ago

Prodigy 5 points

Hello Paul,

You might consider the following circuit.
Use a low Iq comparator to drive the enable pin of a load switch.
The LED portion may be removed.

LMP7300 is a low Iq comparator with built in reference and hysteresis.
This will monitor the battery voltage.
There are battery monitoring examples in the data sheet.

The comparator output will drive the Enable pin of a TPS22930 load switch.
This is a low Iq Load Switch with very low ON resistance.

0 Paul Kilcoyne over 6 years ago in reply to Ed Walker

Prodigy 40 points

Hi Ed,
thanks for the detailed reply. I'll look into purchasing those two items.

Regarding the load switch, will it be able to pass 1amp, my load takes an average of 500mA but can go higher?

Thanks,

Paul

0 Paul Kilcoyne over 6 years ago in reply to Paul Kilcoyne

Prodigy 40 points

Also, what does "low Iq" mean?

0 Aleksandras_Kaknevicius over 6 years ago in reply to Paul Kilcoyne

TI__Genius 15710 points

Hi Paul,

The TPS22930A load switch is capable of supplying up to 2A, so 1A is well within its specs.

Iq is short for "quiescent current", and this is the amount of current the load switch uses when turned on. The TPS22930A has a quiescent current of less than 3uA (typ).

ISD is "shutdown current", and this spec is the amount of current the TPS22930A uses when turned off. For this device, the shutdown current is less than 1uA (typ).

Thanks,

Alek Kaknevicius

0 Paul Kilcoyne over 6 years ago in reply to Aleksandras_Kaknevicius

Prodigy 40 points

Thank you Alek,
how can I achieve my hysteresis off voltage of 2.8v and turn on voltage of 4.0v ? Can you show me how to calculate the values of the resistors and if I need any more components i.e. capacitors etc.?

0 Ed Walker over 6 years ago in reply to Paul Kilcoyne

Prodigy 5 points

Paul, the LMP7300 datasheet has design examples with calculations.
These show how to approach designing with a comparator.

The examples will provide a baseline to apply for your design.

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Choosing the right load switch for battery hysteresis