SBOU268 November 2021 OPA593
Connect the intended voltages or signal sources to the OPA593EVM VIN+ and VIN– jacks using a 50-Ω coaxial cable with standard male BNC connectors for each jack. In most cases, the easiest connection method for the Improved Howland current pump is to connect the output load to the J12 VOUT terminal block and the respective GND. To monitor the current (±) being provided by the OPA593 output, connect an ammeter in series with the load. Connect and apply the required supply voltages to the V+, V–, and GND jacks. Turn on the input voltage or signal source (or sources) and verify the circuit functions as expected.
The IOUT current is a function of the difference in voltages or signals applied to VIN+ J9 and VIN– J5. For the specific condition set up on the OPA593EVM where Ri1 = RF1 = R4 = Rhcp1 = 10 kΩ, the transfer function is simply:
Riso2 = 49.9 Ω is a constant that scales the IOUT output current. The scaling is different when Riso is set to a different value. Select the value of Riso2 so that the current range coincides with the OPA593 data sheet specifications.
Practically, the OPA593 improved Howland current pump circuit can provide the IOUT current through a very-low load resistance of a few Ohms. The high-end voltage is limited by the op amp output voltage compliance range, which is in proportion to the supply voltages being used.