Simple Li-Ion monitoring circuit

[arybinsky]

Hello,

I have a 7.4V Li-ion battery (or rather a battery pack). It is
connected to the 3.3V DC-DC converter which runs the rest of my
circuit.

From what I've found out, I need to shut down the whole circuit when

the battery voltage drops below 6V.
The DC-DC converter has enable pin, so I've figured out I just need to
connect the monitoring circuit to this pin.

What kind of monitoring circuit would you recommend? I really need
something simple, it may be an integrated circuit.

Or maybe it is possible to put this circuit between the battery and
the DC-DC converter? So it blocks any current passing, when the
battery is low?

 

[martin griffith]

Hello,

I have a 7.4V Li-ion battery (or rather a battery pack). It is
connected to the 3.3V DC-DC converter which runs the rest of my
circuit.

the battery voltage drops below 6V.
The DC-DC converter has enable pin, so I've figured out I just need to
connect the monitoring circuit to this pin.

What kind of monitoring circuit would you recommend? I really need
something simple, it may be an integrated circuit.

Or maybe it is possible to put this circuit between the battery and
the DC-DC converter? So it blocks any current passing, when the
battery is low?

check out Texas Inst. TL7702
or google for voltage supervisors


martin

 

[AJ]

Hello,

I have a 7.4V Li-ion battery (or rather a battery pack). It is
connected to the 3.3V DC-DC converter which runs the rest of my
circuit.

the battery voltage drops below 6V.
The DC-DC converter has enable pin, so I've figured out I just need to
connect the monitoring circuit to this pin.

What kind of monitoring circuit would you recommend? I really need
something simple, it may be an integrated circuit.

Or maybe it is possible to put this circuit between the battery and
the DC-DC converter? So it blocks any current passing, when the
battery is low?

I have used the MAX8212 in the past, you can get them from Digikey

Regards


AJ

 

[Terran Melconian]

From what I've found out, I need to shut down the whole circuit when
the battery voltage drops below 6V.

Anywhere between 5.8 and 6.6 should be fine, and there's almost no
energy to be had between those voltages (very steep slope). This means
you can use cheap, high-tolerance parts to set your cutoff with very
little loss of usable energy.

All you need, then, are two resistors, a voltage reference, and a
comparator. The voltage supervisory chips suggested by others combine
the reference and the comparator without costing much more, although
they may be more complicated than what you need and I haven't looked at
their power consumption.

I would recommend looking at the quiescent current of whatever you pick
- you don't want your cutoff circuit itself drawing the battery down
below 2v per cell and ruining it even after the main circuit has been
shut down.