SBOA437A October   2020  – February 2023 INA1620 , INA592 , INA597 , OPA191 , OPA192 , OPA196 , OPA197 , OPA310 , OPA990

 

  1.   Abstract
  2.   Trademarks
  3. 1Discrete Improved Howland Current Pump – Design 1
  4. 2Discrete Improved Howland Current Pump With Buffer – Design 2
  5. 3Integrated Improved Howland Current Pump - INA592 and Buffer – Design 3
  6. 4Integrated Improved Howland Current Pump - INA592 and Settable Gain – Design 4
  7. 5Design Needs and Considerations
  8. 6Operational Amplifier Considerations
  9. 7References
  10. 8Revision History

4 Integrated Improved Howland Current Pump - INA592 and Settable Gain – Design 4

Figure 4-1 Integrated Improved Howland Current Pump With INA592 and Settable Gain

#GUID-C54F3CE8-30FC-44F0-9560-D4419C93CB88 shows the same integrated design of an Improved Howland current pump as GUID-587C0C58-C157-4D41-A33E-1E2A707DF12B.html#GUID-3FE77835-F319-4EFB-B85C-22ECC63E0F0C; the only difference being that the feedback op amp has a settable gain compared to the unity gain of the buffer configuration. This gain configuration gives the ability to design for different values of Vshunt for the same input voltage difference, which was limited with GUID-587C0C58-C157-4D41-A33E-1E2A707DF12B.html#GUID-3FE77835-F319-4EFB-B85C-22ECC63E0F0C. Iload can now be calculated using #GUID-573B0A03-C43B-458A-ADCA-DFD01C422A3D.

Equation 5. GUID-20200916-CA0I-DZRJ-LSFX-6LQFZN8MPZFR-low.png
Equation 6. GUID-20200916-CA0I-VJMT-VSRR-S6G7V5D8GN3S-low.png

Benefits: The benefits to this configuration are the same as in GUID-587C0C58-C157-4D41-A33E-1E2A707DF12B.html#GUID-3FE77835-F319-4EFB-B85C-22ECC63E0F0C; with the added benefit of being able to vary the Vshunt voltage as discussed above. Having the ability to adjust the voltage across the shunt resistor allows the circuit designer more freedom to set the output headroom of the circuit while still benefiting from the precision and high performance of the INA592.

Disadvantages: One disadvantage with this configuration could be the size of the circuit since two op amps and two external resistors are used in the design. This also leads to a slightly more complicated design than the previous three configurations. Due to non-ideal external resistors (Rf, Rg), gain error can be expected, which affects the current accuracy of the circuit.