2.2.1 Current Monitor

The Current Monitor in Fusion measures current by sensing the differential voltage across an external resistor connected between a pair of Voltage and Current input channels. This peripheral requires two channels—one of type V (Voltage) and one of type C (Current)—and these channels must be mapped to adjacent package pins.

The differential voltage across the resistor is amplified by a factor of 10× before being applied to the analog‑to‑digital converter (ADC). No prescaling is applied to the differential voltage measurement. The measured voltage difference must be less than the reference voltage (VREF), whether an internal or external reference is used. You must select an external resistor value that satisfies this condition.

The differential amplifier gain in the Current Monitor is 10×. ASB assumes that a series resistor is used for current measurement. The differential amplifier measures the voltage drop across this resistor (up to 256 mV when using an internal reference of 2.56 V), which is proportional to the current flowing in the direction AV → AC, according to: I=ΔV/R formula.

The Voltage channel in the pair can also be used as a Voltage Monitor to measure the actual voltage present on the Voltage input.

For information on digital filtering factor, acquisition time, and comparison‑flag specifications, see Configuring Current, Voltage, and Temp peripherals section.

Figure 2-16. Configure Current Monitor Peripheral Dialog Box
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Current Monitor Configuration Option
The following controls are specific to the Current Monitor peripheral:
  • External Resistor: Specifies the value of the resistor connected externally across the Voltage–Current channel pair. ASB uses this value to convert user‑specified current thresholds into equivalent voltage thresholds.
  • Polarity: Sets the measurement polarity to positive or negative. The associated Voltage values must match the selected polarity. ASB issues a warning if the Voltage values do not match the specified polarity. When negative polarity is selected, the prescaler option for the associated Voltage Monitor defaults to the prescaler path.
  • Maximum Voltage: Specifies the maximum anticipated voltage measured by the Voltage Monitor pad associated with the Current Monitor. The valid range is –10.5 V to +16 V (the voltage range is not bipolar). The ADC itself measures voltages in the range 0 V to VREF. When using the internal voltage reference, VREF = 2.56 V. ASB automatically configures the prescaler in the analog block (AB) to maximize the usable voltage range for this peripheral. ASB also post‑scales the digital ADC result so that the reported value corresponds to the user‑specified voltage range.