What is the maximum charge current and discharge current of R5460 Series IC ?

[Sai teja]

Hello, I am using "R5460N214AF" IC for 2 cell Li-Ion battery protection. According to datasheet, excess discharge current threshold is 0.2 V and excess charge current threshold is -0.2 V.

I would like to understand these voltage thresholds in terms of currents. Some one please explain how to understand max charge current and discharge current supported by the IC.

I am attaching the datasheet for your reference.

https://www.mouser.in/datasheet/2/792/r5460-e-1085730.pdf

Let me know if I am not clear and please help me in this regard.

Thanks.

[timpattinson]

From a quick read of the datasheet it only measures voltage so only provides under/overvoltage protection.

There is no intrinsic current limit because it does not measure the current and it does not pass through the device.

It uses two external MOSFETS to disconnect the battery so the practical current limit will be determined by what MOSFETS you use (I2R hearing or acceptable voltage drop) (and what is the biggest MOSFET this chip is able to drive)

Edit:
Reading the datasheet again it does offer short circuit and over current protection. I belive this is done by measuring the voltage drop across the MOSFETS as there is no current shunt in any of the example schematics.

In this case the current limit is dependent on the Rds of the MOSFET ( the current that causes I*Rds to be greater than the detection threshold in the data sheet)

Sent from my SM-G930F using Tapatalk

[Siwastaja]

Rds(on) measurement. I = U/R. Plug in the total Rds(on) of the two MOSFETs in series. Note when they get hot, the Rds(on) rises and the current limit gets lower than what you calculate at room temp, but this is often desirable.

You select the current limit by choosing suitable MOSFETs. Remember to calculate the thermal dissipation and that the MOSFETs don't blow up just a tiny bit below the current limit threshold (ie., Vds=0.2V).

[Sai teja]

Hi Siwastaja and timpattinson,

Thanks for both of you for your response.
 
For "R5460N214AF-TR-FE" IC, values of over discharge current threshold(0.2V) and over charge current threshold(-0.2V) are same. According to above theory, maximum charging current and maximum discharge current will be same.
Can't I design the protection circuit having different max charging current limit and max discharge current limit with "R5460N214AF-TR-FE" IC ?

Awaiting your reply.

[Siwastaja]

Yeah, the limits will be the same. Note that 0.2V drop over the MOSFET is quite big, almost 3% efficiency loss in the MOSFETs only. This protection limit is clearly not meant to be something you normally work close to. It's only to protect from very large overcurrent, such as short circuit. You are expected to provide proper, accurate current limiting by controlling the charger and the loads.

I agree that an asymmetrical limit would be more handy, since the safe operating current of the cell is asymmetrical as well (typically around 1:4); you can't do it with this chip.

[Sai teja]

Hi ,

Generally Rds-on for FETs vary depending upon external factors like operating voltage, temperature. Can you please, Rds-on  at which conditions is to be chosen?

Regards,
Sai teja.

[timpattinson]

Are you making a hobby product? It should work at room temperature for the typical datasheet values of the MOSFETs.

Commerical product? 0 to 85C
Industrial? -40 to 100C

Additionally you will want to look at the max/min (not just typical) datasheet values and make sure your product will work under these cases
(i.e. at the absolute max Rdson will it trip at a normal current or overheat, at the absolute min Rdson will it trip at all?)