OPA189 Datasheet, PDF (21/34 Pages) Texas Instruments – Precision, 36-V, 14-MHz, MUX-Friendly Low-Noise, Rail-to-Rail Output, Zero-Drift Operational Amplifiers

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OPA189, OPA2189, OPA4189
SBOS830 – JUNE 2017
Typical Applications (continued)
9.2.1.1 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
9.2.1.2 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.
For a successful design, pay close attention to the dc characteristics of the operational amplifier chosen for the
application. To meet the performance goals, this application benefits from an operational amplifier with low offset
voltage, low temperature drift, and rail-to-rail output. The OPAx189 CMOS operational amplifier is a high-
precision, ultra-low offset, ultra-low drift amplifier, optimized for low-voltage, single-supply operation, with an
output swing to within 15 mV of the positive rail. The OPAx189 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 family appropriate for precise dc control. The rail-to-rail output stage of the
OPAx189 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, which is 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).
9.2.1.3 Application Curves
Figure 11 shows the measured transfer function for the high-side voltage-to-current converter shown in
Figure 10 .
0.1
Load
0.075
0.05
0.025
0
0
0.5
1
1.5
2
Input Voltage (V)
D001
Figure 11. Measured Transfer Function for High-Side V-I Converter
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