8.2.1.2 Detailed Design Procedure

The V-I transfer function of the circuit is based on the relationship between the input voltage, V_IN, and the three current sensing resistors, R_S1, R_S2, and R_S3. The relationship between V_IN and R_S1 determines the current that flows through the first stage of the design. The current gain from the first stage to the second stage is based on the relationship between R_S2 and R_S3.

This application benefits from an operational amplifier with low offset voltage, low temperature drift, and rail-to-rail output. The OPAx187 CMOS operational amplifier is a high-precision, ultra-low offset, ultra-low drift amplifier, optimized for wide-voltage, single-supply operation, with an output swing to within 5 mV of the positive rail. The OPAx187 family uses chopping techniques to provide low initial offset voltage and near-zero drift over time and temperature. Low offset voltage and low drift reduce the offset error in the system, making this device appropriate for precise dc control. The rail-to-rail output stage of the OPAx187 makes sure that the output swing of the operational amplifier is able to fully control the gate of the MOSFET devices within the supply rails.

A detailed error analysis, design procedure, and additional measured results are given in reference design TIPD102, a step-by-step process to design a High-Side Voltage-to-Current (V-I) Converter.

	For step-by-step design procedure, circuit schematics, bill of materials, PCB files, simulation results, and test results, refer to TI Precision Design TIPD102, High-Side Voltage-to-Current (V-I) Converter (SLAU502).