Can nRF52 Differential ADC Measure voltage higher than VDD?

[Howard]

I want measure the current of a device over a resistor. It is connected to 5V which is over VDD(3V) of nRF52 Chip. 5V--->10ohm--->Device the differential voltage of this register will not exceed VDD(3V) because current is below 100mA.

What should I do to implement this using nRF52's ADC?

[Songplus]

U can't measure current using ADC Directly，U should use a IC to C/V convert

[Howard]

Is that because of over-voltage? I can put the resistor to ground side. Whatever, Could you recommend one kind of C/V convert IC? Thanks a lot!

[Vala]

Hi Howard,

You can measure the current using a resistor in the path of power supply and sensing the voltage difference between the two pins of the resistor. Also, I wouldn't personally go with placing the resistor at the ground side of the device. It would introduce grounding error in the system. You can either power the other device with 3V, if it is possible or use an external component like an op-amp to produce the difference and then read it by the ADC. I didn't find any specific number in the datasheet regarding the maximum allowable input of ADC pins. But I found (1) the allowable input for I/O doesn't let you do this, (2) the value of the ADC reference can either be internal or VDD, which in any case doesn't let you use the internal ADC for this purpose. Hope this helps.

[jcormier]

Howard, Note the Laird devkit uses a current shunt IC. No idea if its power efficient but its a start. They don't actually hook it up to the BLE chip but you could.. cdn.lairdtech.com/.../BL652 Dev Kit User Guide.pdf (See 9.1 Current Consumption Measurement) INA216

[Howard]

@Vala, and Jcormier, thank you very much for your information!