Source Impedance matching using voltage divider for monitoring battery voltage.

[Hardik]

Hello All,

I am using NRF51822 controller in my design.

I want to monitor battery voltage using ADC pin with voltage divider.

I have LIPO battery with 3.7V and 200mAH rating.

Can you suggest how to match source impedance values and what can be maximum values of resistor that can be used to make resistor divider.

Suggest any reference circuit.

Also looking for option of FET with Voltage divider.What parameters are to be taken care.

Thanks

Hardik Rawal

[Jørgen Holmefjord]

Hi,

I would recommend that you take a look at the blog post "Measuring Lithium battery voltage with nRF51".

Best regards,
Jørgen

[Hardik]

Hi,

Many thanks for sharing very useful information and making me learn concept of ADC for battery monitoring.

Few doubts related to source impedance mentioned in the Datasheet of NRF51822.

In Datasheet Source Impedance is given less than 5Kohm.

Does it mean that We need to have resistor divider with output impedance less than 5KOhm? I understand that if we take higher (MOhm) resistor divider values may result in high output impedance, correct? please guide me If I have calculating something wrong.

Its DC sensing so does capacitor help to match the impedance? How?

we need to have very low (nA) current consumption by resistor divider circuit. Should I consider FET in this circuit? Please suggest.

Thanks

Hardik Rawal

[Jørgen Holmefjord]

Yes, the capacitor helps with this. As you can see, the resistors in the blog post is much higher than 5k Ohm. Please have a look at this thread.