OPA187_17 Datasheet, PDF (21/35 Pages) Texas Instruments – Drift, Low Power, Rail-to-Rail Output 36-V Operational Amplifiers Zero-Drift Series

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OPA187, OPA2187, OPA4187
SBOS807 – DECEMBER 2016
Typical Applications (continued)
8.2.1.1 Design Requirements
The design requirements are:
• Supply voltage: 5 V DC
• Input: 0 V to 2 V DC
• Output: 0 mA to 100 mA DC
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).
8.2.1.3 Application Curves
Figure 42 shows the measured transfer function for the high-side voltage-to-current converter shown in
Figure 41.
0.1
Load
0.075
0.05
0.025
0
0
0.5
1
1.5
2
Input Voltage (V)
D001
Figure 42. Measured Transfer Function for High-Side V-I Converter
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