BATTERY KILL SWITCH

R_K

Intellectual 385 points

Other Parts Discussed in Thread: CSD86311W1723, CSD85302L, CSD85301Q2

Hi,

We are planning to use n-channel e mosfet between battery and rest of the circuit.

We need the mosfet to turn off when gate voltage is low and turn on when gate voltage is high.

Current rating should be more than 1A with low Rds-on and voltage rating should be more than 4.2V

Also the mosfet should be bidirectional (drain to source as well as source to drain). Basically when mosfet is ON we need it to support charging of battery as well as discharging supply to the circuit depending on voltage level whichever is high.

Can you suggest few n channel e-mosfet and also let me know if this configuration will work?

Thanks in advance.

Regards,

Rahul

over 6 years ago

0 Vish Nadarajah over 6 years ago

TI__Expert 6085 points

Rahul, Battery Kill implementation on the high current path can have varying topologies. The FET selection will depend on the peak short-circuit current of the battery and Load too. Please refer to the active secondary-protection switches that work in conjunction with primary protector based and in-line fuse(depending on the industry-standard ). The battery voltage, OV, I_shortcircuit, I Load, etc come into the decision of the selecting the FET.

TI has many protectors and secondary protector in the bq769x0 and bq7718x family

hope this helps out

vish

0 Chris Bull over 6 years ago

TI__Expert 7435 points

Rahul,

Thanks for coming to us and considering our MOSFETs.

Looking at the description is seems as though you have a single cell LiIon battery system and as such I assume you will want a part that operates down to a Vgs of 2.5V to manage maximum battery life as well as the 4.2V.

In addition, I assume you can not have the body diode conduct and need to have devices that are back to back in the configuration as shown here:

You can tie gate one and gate 2 together to turn each device on and off at the same time. You need to have back to back devices to ensure the body diode of one FET does not conduct when polarity in charge/discharge flips on the Source/Drain.

One very small device we have that will easily handle 1A is the CSD85302L and has resistances rated @4.5Vgs and 2.5Vgs, this is a chipscale silicon based package. Another device that you may want to consider would be the CSD86311W1723. If your manufacturing environment would prefer a plastic encapsulated device vs these silicon only packages then I would suggest the CSD85301Q2, this is a dual SON2x2 and can configured on the PCB to replicate the circuit above.

Here is also a reference design that may be of interest for a battery mgmt single cell LiIon, in this case it uses a pch MOSFET that performs the same function as the nch device you are requesting here.