Proper undervoltage lockout for battery powered device

Hi Guys,

I am thinking how to better realize disabling power of circuit in undervoltage situations.
Many DCDC converters have UVLO at about 2.8V that could be suitable for 1 cell battery, but I am designing 12V battery powered circuit.
Some DCDC also have adjustable UVLO, but because I need to use large resistors for UVLO voltage divider so that I don't drain battery more I am will get too large hysteresis voltage Uhyst=Rlarge*Ihyst

Can you recommend the best way of realizing undervoltage lockout with low power consumption?

Kristaps

What DCDC converter are you looking at?
How large is Rlarge?
Any other specifics you can add?

I am looking at tps54202
If I need 11.8V/11.5V ON/OFF thresholds then v divider should use 6.3k+720Ohm resistors (that's 1.6mA)
Increasing ON voltage to 11.9V reduces current to 0.15mA and 12V to 80uA.

And that's all with my circuits target idle current (between wakeups) of tens of uAmps.

I could make divider with large turn ON voltage (allowing use large resistors = less current) and use button pullup to manually enable DCDC, but that's hack I would like to avoid.

Maybe I want too much
I am interested to hear what others suggest or use in such situations.

I am building LoRa node powered by small 12V Lead battery (thought it will better in -20C temperatures than LiIon and safer)
I am not going for sub uAmp consumptions here, but would like to achieve maximum power saving.

Hi,

If I need 11.8V/11.5V ON/OFF thresholds then ...

Click to expand...

Depending on battery chemistry you may go lower with the OFF threshold..
But why switch ON with that 300mV small hysteresis, this means about no energy hysteresis in the battery.
It may cause ON/OFF/ON/OFF.... switching...

Klaus

I guess I missed something.

The tps54202 is a buck regulator. Since you are using a 12 V lead acid battery, what is the desired output voltage?
There is no reason to shutdown until the battery voltage is 3 V above output voltage based on table 1 page 13 of the data sheet.
The shutdown also depends on the properties of your battery, and the battery charger.

I could not find any specification on minimum Vin - Vout.

Probably I didn't clarified my need clearly.
I am planning to use UVLO to prevent battery from discharging too much. That's why power consumption of switched off DCDC is important.
Probably I could go with larger hysteresis and have x0uA consumption in turned off state.

Thanks guys for your replies.

If you have more Ideas for low voltage battery cut off, please post here.