Separate AIN to check battery level is OK?

[Jake]

Using nRF51822.

I use external DCDC to supply concurrent 3.1V for VDD(PIN1). Then I have no way to check bettery level. So I connect battery and AIN4(p0.03) separately, directly.

Does this circuit can make side effect, as if radio performance?

In my test, if battery level is under 2.87V to AIN4 and 3.1V to VDD then TX signal is distorted and BLE connection is closed.

[Einar Thorsrud]

I don't really understand why you get bad radio performance when measuring with the ADC. Are you confident that that is the case? As you are using an external DC/DC there will be some ripple on the supply voltage. Can you measure how much ripple you have on the VDD pins?

How have you configured the ADC in your case? Without any external components you should configure it with 1.2 V VBG reference and 1/3 prescaling. Also, have you seen the Measuring Lithium battery voltage with nRF51? In order to get precise measurements, you should use an external voltage divider and capacitor, as described in the blog post. Note that none of this explains bad radio performance, though.

[Jake]

Sorry for late reply.

As you mentioned I checked ripple on the VDD pins. And I found too much of ripple in VDD, DCDC generated.

I asked this to provider of DCDC converter, and they suggested correct value of capacitor of VDD and Feedback line.

Now it it works.

Thank you Einar Thorsrud.