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OPA855: Howland current pump

Jonghyun KIM
Prodigy 10 points

Part Number: OPA855
Other Parts Discussed in Thread: OPA830, LMH6611

Hello, E2E

I'm jonghyn

I want to design howland current pump using TI product. so i download PSPICE for TI and simulate it.

My design target is maximum 0.75mA +- 0.75mA (1kHz - 100MHz) and driving load impedance, 10 ohm - 1.6kohm. 

1. So as shown attached file below, when i use ideal OPAMP and use 1kohm, I can get proper calculated load current (0.5mA +- 0.223mA). but i change ideal OPAMP to OPA855 with VCC = 3.3V & VEE = 0V, DC current is move to 2.75 mA. what happen to it?

2. Can you recommand to me suitable OPAMP product for me?
    (Maximum current target: 0.75mA +- 0.75mA (1kHz - 100MHz) and Load voltage is change to 550 ~ 800 mV)

3. If you recommand to use improved Howland current pump using additional buffer (, Hope to recommand proper buffer OPAMP.

 

 

Screenshot_20260209_110450.png

  • 0
    TI__Mastermind 20690 points

    Hi Jonghyn,

    There are a few reasons the OPA855 is not working in this circuit. One concern is that this device is decompensated meaning it requires a minimum noise gain of 7V/V which would lead to stability issues if set below 7V/V. Another issue is that this device is not rail to rail meaning its input common-mode voltage range and its output range is limited. By having a supply of 3.3V you considerably limit these ranges. I would consider looking into our OPA830 or our LMH6611. These devices are rail to rail and should have the bandwidth you require. I would keep in mind your input and output ranges when simulating your circuit as this is usually something that is easily violated with these circuits. Regarding a buffer option you could consider the same device (OPA830 or LMH6611) as these devices can function as a buffer.

    Best Regards,

    Ignacio