1.3.1 Current Monitor

The current monitor in Fusion measures current by measuring the differential voltage across a resistor between a pair of Voltage and Current Input channels. This peripheral requires two channels, one of type V and one of type C, and they must be on adjacent package pins.

The differential voltage is multiplied by 10x before it is applied to the ADC; there is no pre-scaling on the differential voltage measurement. The difference in voltages must be less than the value of Vref, external or internal. You must choose an external resistor that satisfies this condition.

The differential amp gain in the current monitor is 10X. ASB assumes a series resistor because it is being used to measure current. The differential amplifier measures the potential/voltage drop (256 mV max if the reference is 2.56V) across the resistor, which is proportional to the current flowing in the direction AV -> AC (I = (change in voltage)/resistance)). The voltage channel in the pair can be used as a voltage monitor to measure the actual voltage that is connected to the Voltage channel.

For more information on the digital filtering factor, Acquisition time, and Comparison Flag Specifications, refer to the Configuring Current, Differential Voltage, Temperature, and Voltage Peripherals section.

Controls unique to this peripheral are the External resistor and >Maximum voltage.

Figure 1-18. Configure Current Monitor Peripheral Dialog Box
???

External Resistor - The value of the resistor that is connected across the Current-Voltage pair, external to the device. ASB uses this value to convert the thresholds into voltages.

Polarity - Sets the polarity to Positive or Negative. The associated Voltage values must match this polarity. ASB returns a warning if the Voltage values do not match the polarity. When you select a negative polarity, the prescaler option on the associated Voltage Monitor defaults to the "Prescaler" path.

Maximum voltage - The maximum anticipated voltage measured by this Voltage Monitor peripheral pad. The range is -10.5V to +16V (the voltage range is not bipolar). The ADC is capable of measuring a voltage range of 0 - Vref. For the internal voltage reference, this value is 2.56V. ASB automatically configures the prescaler in the AB Analog Block for this peripheral to maximize the available voltage range. ASB also post-scales the digital result of ADC conversion so that it returns a result in your specified range.