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Original question:

OPA564: How to simulate stability of Howland current source using opa564

OPA564: cost down replacement for motor drive

BX27
Genius 3870 points
Part Number: OPA564
Other Parts Discussed in Thread: OPA521, OPA2673

Hi there, we used two OPA564 configured as improved howland current source, to drive two step motor coils (8.5ohm + 4.1mH), and we hope to find replacement for cost down in next HW version.Current version SCH and some key info is below （OPA564 on third page）.

Input sine wave is 500HZ or less, with amplitude 2V or so (can be conditioned).

Power consumption is not a big concern, I_output should be >500mA to drive the motor coil, drive power Vs = +/-10V,  and I searched in TI website, found possible candidate : OPA521 or OPA2673, which are cheaper but claimed to be used in PLC application, so I am not very sure if they are applicable.

Or D-Class amplifier which can drive coil might be usable. 

Hope TI experts could help recommend some devices. Thanks. 

  • 0
    TI__Guru* 93105 points

    Hello Yi,

    When it comes to product substitutions for cost reasons we pull in our Precision Amplifiers Marketing Engineers because cost is one of their areas of expertise. I will inform them about this e2e post.

    The OPA521 gain is set internally to -7 V/V, but there is access to the summing node and output pins so with some creative external resistor connections you should be able to realize the Improved Howland Current Pump configuration. That said, there isn't the usual open-loop Bode plot in the OPA521 datasheet.That is likely because it is intended for the PLC closed-loop gain of - 7 V/V application. The section 6.8 Typical Characteristics cure, Figure 1, Closed Loop Gain vs Frequency, shows no peaking so the op amp appears to be fully compensated. Be aware that changing the internal configuration from a gain of -7 V/V to the current pump could bring somewhat different ac performance from what was obtained with the OPA564.

    The OPA2673 is a High-Speed Amplifiers product and since we don't have intimate knowledge or cost information for that op amp in Precision Amplifiers it is best to contact them.

    Regards, Thomas

    Precision Amplifiers Applications Engineering