Battery Monitoring Circuit

[Ricky A. Rosa]

Hello,

In the product specification for the npm1100 there is an optional battery monitoring circuit schematic on page 39. I'm having trouble understanding why there are two transistors needed. As I understand, BAT MON ENABLE pin enables Q1A, and Q1A enables the Q1B which enables the monitoring circuit. But why is the intermediate step necessary. Why not have only one transistor enable the monitoring circuit?

Best,

Ricky

[Jared]

Hi there,

I think it might be related to the leakage, but I have to double check this internally.

Will be back with more.

regards

Jared

[Ricky A. Rosa]

sounds good! thanks

[Jared]

Hi,

Additional stages would not decrease leakage current. From our HW engineers:

To fully switch off the Q1B PMOS its gate-source voltage needs to be close to 0V.  If the nRF5x is powered from 1.8V and the battery is at 4V, it would be impossible to switch Q1B off, as the minimum Vgs is 4V-1.8V = 2.2V. 

regards

Jared