Power latching Circuit help needed for 4.2V Li Ion Battery

Thread Starter

mishra87

Joined Jan 17, 2016
909
Hello Guys,

I was looking for latching circuit and i found below circuit.

Case1: When SW S1 is pressed momentarily below is current path . M1 will turn ON and Vbat appears at Vin marked red. Once Vin makes MCU wakes up and GPIO pin enable the gate of M2 via internal pull up. GPIO pin kept as input pin.
1617132834522.png

Case2. If some pressed sw S1 for longer duration. The MCU GPIO see low and it pull low(open) to it and now M2 gate see low and OFF.
Until now i have understood this.

The same application i wanted to use but I see the problem here.

Lets say if S1 if pressed falsely for longer time so it will drain the battery by 4.2V/100K= 42uAA and which is not good.

So could anyone help me to solve this problem ?

Thanks in Advance!

Best regards,
 

sghioto

Joined Dec 31, 2017
2,395
Lets say if S1 if pressed falsely for longer time so it will drain the battery by 4.2V/100K= 42uAA and which is not good.
There will also be current through R3 and the internal pullup on the GPIO pin. As long as S1 is closed the output from M1 is High
 

Thread Starter

mishra87

Joined Jan 17, 2016
909
Unless the battery is really small, it will take a very long time to drain with only a 42μA load.
Hi,
Thanks for your requirement.
The standby current requirement is 10uA.

Could you suggest some improvements or any other idea ?

As stated in post#3 M1 will always on unless battery is completely drained.

Regards,
 

Thread Starter

mishra87

Joined Jan 17, 2016
909
There will also be current through R3 and the internal pullup on the GPIO pin. As long as S1 is closed the output from M1 is High
Hello,
GPIO may be disabled since mcu LDO will be off.

Could you please suggest any other approach for the same ?
Regards,
 

Thread Starter

mishra87

Joined Jan 17, 2016
909
OK. So the enable pin of the LDO is controlled by another GPIO pin correct?
Does Vin power the entire micro or just a wakeup pin?
I think now we are on the same page as in old thread.
Vin of this pin will control EN of LDO and EN is also controlled by MCU DO.

So again same problem. After MCU shu down the EN pin it will be in high impedance mode.

Also one additional feature required to detect the switch status via mcu.
May be I have to think more to implement the logic.

I may thinking how mobile phone company implement this as I see long press the mobil sw, the mobile phone completely goes in standby mode unless and until sw press event not given.
 

sghioto

Joined Dec 31, 2017
2,395
I'm trying to understand the sequence of operation. Below is my interpretation of your design.
Latch enables LDO...LDO powers MCU...MCU disables LDO at program conclusion.
Please correct as needed.
1617156645807.png
 

Thread Starter

mishra87

Joined Jan 17, 2016
909
I'm trying to understand the sequence of operation. Below is my interpretation of your design.
Latch enables LDO...LDO powers MCU...MCU disables LDO at program conclusion.
Please correct as needed.
View attachment 234060
Hi,
Thank you very much for your effort.
Yes it is correct.
One additional remark Where ever you add sw. The sw status will be deducted by mcu.
My thought was as same you implemented but at end we have completely turn off the device in standby mode.

There could be some other way to do it.

Thanks again.
 

Thread Starter

mishra87

Joined Jan 17, 2016
909
Okay.
So this schematic will have some problem.There is always current flow via R1 and D2 when sw is pressed lets say for longer duration as you already mentioned.
I=4.2/100K apart from LDO stand by current.

Thanks
 

Thread Starter

mishra87

Joined Jan 17, 2016
909
I don't understand your issue with the 42ua.
Is someone going to be pushing this switch for hours on end?
See 2000mAH battery and stand by current should not be greater than 10uA. So I wanted to reduce it below 10uA.
May be some latching IC with low power can do the Job.
 

Thread Starter

mishra87

Joined Jan 17, 2016
909
I don't understand your issue with the 42ua.
Is someone going to be pushing this switch for hours on end?
Again I see the same problem since M1 is always on which will give always high signal to LDO even MCU pull EN in down and then become floating.

I still do not understand this problem ?

Thanks for your all conversations.
 
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