Input Voltage (V)

0

0.5

1

1.5

0

0.025

0.05

0.1

Load

0.075

2

D001

21

OPA188

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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, VIN, and the three

current sensing resistors, RS1, RS2, and RS3. The relationship between VIN and RS1 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 RS2 and RS3.

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 OPA188 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 devices in the OPA188 family use 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 OPA188 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 Precision

Design Guide TIPD102, High-Side Voltage-to-Current (V-I) Converter.

9.2.1.3 Application Curves

Figure 45 shows the measured transfer function for the high-side voltage-to-current converter shown in

Figure 44 .

Figure 45. Measured Transfer Function for High-Side V-I Converter