Sample circuit of high precision programmable current source from Analog Devices. Link here (PDF)
Digitally controlled current sources are critical functions in a variety of applications, such as power management, solenoid control, motor control, impedance measurement, sensor excitation, and pulse oximetry. Here we describe three current sources with serial interface digital control using DACs, op amps, and MOSFET transistors.
The DACs selected are high resolution (14- or 16-bit), low power CMOS with standard serial interfaces. The two DACs (AD5543 and AD5446) are both compatible with most DSP interface standards and also SPI, QSPI, and MICROWIRE. The external reference voltage input allows many output level variations, up to 10 V. The combination of parts represents industry-leading small PC board area, low cost, and high resolution. The three designs offer low risk solutions and use industry-standard parts.