When deciding whether to employ a parallel improved Howland pump configuration versus a conventional parallel buffer configuration, there are many factors that must be considered. How well one arrangement works when compared to another is highly dependent on the amplifier used, and how it interacts with the circuit load. Which circuit approach is best for solving a given problem is thus dependent on the problem nuances and available components. It should be noted that to achieve the best resilience to offset and ballast resistor mismatch, the pumps must be operated in an attenuating gain, which means the error amplifier will need to have sufficient headroom for cases where the desired output current is very high.

The parallel improved Howland pump circuit is best suited for situations where the trace resistances of the channels are expected to be mismatched, such as when the channels are scattered around the board; cases where the offset of the amplifier to be used is fairly low; and cases where the required bandwidth is low, or the load is resistive rather than capacitive. For best results the driving amplifier selected should be well suited to driving high output currents and capacitive loads, such as the ALM2402-Q1, ALM2402F-Q1, or ALM2403-Q1. It is important that the gain setting resistors of the channels are well matched, and so the INA1620 is another excellent option for solutions requiring high integration, with its multiple on-chip precision matched resistors and 100mA drive capability.

While the parallel pump circuit does require more components than the conventional buffer circuit, its inherent immunity to trace mismatch means the circuit can be instantiated wherever there is space on the board – the channels do not need to be located directly next to each other or even on the same circuit board to share the load fairly evenly, and all of the driver channels can actually be located quite far from the load and still operate in an accurate fashion as long as the error amplifier takes its feedback from very close to the load.