28.4.1 Basic Operation of the 10 µA Source

The primary application of this source is to generate current to create an external voltage. This voltage can then be measured with the internal ADC or used to bias external circuitry. This class of source can only supply (source) current. To generate an external voltage, an external resistor is connected between the current source pin and AV_SS (refer to Figure 28-2). The current flow generates a voltage across the R_EXT resistor (refer to Equation 28-1 and Enabling a 10 µA Source). Multiple sources can be paralleled, as needed, to increase current.

Figure 28-2. 10 µA Current Source

Equation 28-1. Equation for Determining the Value of R_EXT

V(R_EXT) = 10 µA × R_EXT

V(_REXT) should not exceed AV_DD – 0.5V typical (see Operating Range).

Enabling a 10 µA Source

R_EXT = 10 kOhms, AV_DD = 3.3V V_PIN = 10k × 10 µA = 100 mv V_REXT << 3.3V – .5V, and therefore, meets the V(R_EXT) requirement


// User code to enable a 10 ua source
BIASCONbits.I10EN0 = 1;				// enable 10ua source channel 0