Hi,Team,
Customer is using LM2904NS to implement a High pass filter.
I checked the VCM is not correct as datasheet limit. Vcm should be less than V+-2.
I modified the Vcm to 1.1v. The TINA simulation shows good result. But on customer's board, the signal is with much distortion.
When reduce the RL from 1Kohm to 200ohm, the output sinal is much better.
The datasheet doesn't describe the relationship between RL and phase margiin.
Do you think if the RL impact the phase margin of the circuit?
Does RL contribute to loop stability?
What is the limitation for the Min RL? output current?
Schematic TINA:
3005.xx_HPF_test.TSC
regards,
Ivan
Ivan,
The "AC ampli6" plot shows peaking just under 100kHz. This suggest low phase margin. Lower resistance loads do increase phase margin a little, but this is not the best approach. I suggest increasing the two resistors on the inverting input leg by 100X and reducing the two capacitors (also on the inverting input leg) by 100X.
The simulation shows no (low phase margin) peaking with this setup.
Regards,Ron Michallick
Regards,Ronald MichallickLinear Applications
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