Battery circuit why these two mosfets

[newbe_always]

The below schematic is taken from this TI reference design. May I know is there any reason for using 2 MOSFETs here.
Hi this link contains the application of the product.This is a Wireless PIR Motion Detector.Here is the design guide.

 

[danadak]

Reverse blocking ? This example is NMOS, but principles apply -

What is reverse-current blocking using external back-to-back MOSFETs? | Toshiba Electronic Devices & Storage Corporation | Americas – United States

Two N-channel MOSFETs are externally connected back-to-back (in a common-source configuration) when a load switch using a gate drive IC needs a function for blocking the current flowing into the load switch in the reverse direction. This function is called reverse-current blocking.

toshiba.semicon-storage.com

But your circuit not back to back, error ?

 

[newbe_always]

This is a TI reference design.

 

[Nigel Goodwin]

This is a TI reference design.

And datasheets and reference designs are commonly full of mistakes

 

[newbe_always]

completely agree

 

[danadak]

Not sure what this circuit is doing....note spice model does call out the body diode in it

 

[danadak]

Why are two MOSFETs used in series in the Lithium-ion secondary battery protection circuit? | Toshiba Electronic Devices & Storage Corporation | Americas – United States

Q: Why two MOSFET in series are required for lithium-ion secondary batteries? A: Two MOSFET are used to realize both the charge and discharge functions.

toshiba.semicon-storage.com

 

[newbe_always]

So the orientation of MOSFET is wrong in the TI reference design

 

[schmitt trigger]

Unfortunately, this wouldn’t be the first time this has happened.

 

[danadak]

View attachment 149761
So the orientation of MOSFET is wrong in the TI reference design

I dont think we know enough about the design intent, but do a sim, see what you
get for currents vs V applied to connector....

 

[newbe_always]

May I know any relation with this.

 

[schmitt trigger]

May I know any relation with this.

Back in the day, before inexpensive EEPROM memory was widely available, the configuration settings were stored in static RAM. And they were kept powered during the main power-off periods via non-rechargeable lithium cells.

As the article you linked mentioned, UL were very paranoid about a schottky diode failure causing current flowing back into the cell, which could potentially cause a fire. Thus a redundant diode was employed. This caused a double diode drop on an already low (compared to 5V) battery voltage. We would have loved to use a P-channel Mosfet instead, but in those days there were no suitable devices for this purpose.

Fortunately static RAM consumption at idle was below minuscule, and the actual schottky forward drop each was a tad above 100 mV, and the circuit would be backed up by a significant amount of time.

However, for the circuit that you show, the coin cell appears to be the primary supply, and therefore two Mosfets in series doesn’t make sense.

 

[crutschow]

So the orientation of MOSFET is wrong in the TI reference design

That's only if the MOSFETs are connected to some type of controller.
It makes no sense when their gates are both connected to ground since, if they are back-to-back, they won't conduct in either direction.