Hi Team,
Good day, we received query from customer and seeking support regarding OPA2180. For me to not miss any information I'll copy the query below.
We are using OPA2180IDR to buffer a signal representing current. The signal is referenced to gnd "0VA", and is negative. The amplifier is configured as an inverter with gain of 1, with VCC=+12V, VEE=0VA. The input signal is waveform is a square wave, 5kHz, stepped from -30mV to -4.0V to -30mV. The output is expected to be +30mV to +4.0V to +30mV. However, we do get this expected waveform.
To assist you to understand the problem better, I have attached images that show schematics, and scope waveforms. Brief description:
1. System ground (earth) is node marked "0VA".
2. Signal generator GND is connected to "0VA".
3. Scope GND is connected to "0VA".
4. Scope CH1 is connected to node "SHUNT-NEG", refer attached ckt 1 of 3.
5. Scope CH2 is connected to op-amp output, node "X42", refer attached ckt 2 of 3.
6. Bypass cap (1uF/25V) is connected very close to package pins, ref attached ckt 3 of 3.
7, Signal generator set up is shown in attached image. Note that sig gen output impedance is non-zero, so there is a slight voltage drop when comparing to scope image for CH1 with sig-gen settings.
7. Waveforms for the input signal, and output signal, are in attached image. There is also a video showing under same test conditions. It would seem that the opamp output is bi-stable, it switches between two very different states.
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The attached photo shows the scope when the output of the op-amp is completely different to what is expected, which causes the rest of the system to not perform as expected.
The schematic reference is "Current Measurement Ckt 2 of 3" (sent previously), but note the following changes:
1. The two capacitors C68 & C69 (0.1nF) were removed prior to this test.
2. Each opamp input (pin 5, 6) has a 1MEG ohm resistor to +12V, this biases each input to about +1V above 0VA, which is the opamp negative supply (pin 4).
The expected opamp output was drawn onto the photo using a photo-editor.
Thank you and looking forward for your kind response.
Regards,
Maynardattachment.zip