We are designing a circuit to measure the current consumed by a Ultra-low power communication module.
The requirement is below:
- Min current = 0.2mA
- Max current = 100mA
- Resolution = 0.005mA (5uA)
We do not need to measure DYNAMIC current, just want to measure AVERAGE current at a specified working condition such as Active, Sleep, Shutdown
Our design proposal is in attached file, that we will use a sensing resistor in series to the load.
I have some questions, please provide clarifications.
1).The sense resistor value selected is 500mOhm. According to my understanding to get 5uA resolution ADC’s 1LSB must be less than or equal to 2.5uV (RsenseCurrent step,ie (500mohm5uA). Please correct me if I am wrong.
- Do I need to use a pre-amplifier after current sense resistor? Imagine I am using an ADC with 24bit resolution and 5V reference then my 1LSB will be 0.3uV, less than the required resolution. Is it possible to connect a buffer after Rsense and connect its output directly to ADC input?
3)If possible could you please suggest IC’s from your company for this application