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I'm using the linear regulator LP2985-50 from TI to power a set of op amps (NE5532). The op amps provide an analog signal to a component that is very sensitive to overvoltages. Upon power up, I first drive the Enable (ON/#OFF) pin of the LP2985-50 low to ensure a soft start while the other components of the PCB (microcontroller, etc) are powering up. Then I drive the Enable pin high to turn on the linear regulator, and I observe a transient of up to 4V at the output of the op amp circuit. Is this the correct way to use the Enable pin on the LP2985-50? How can I avoid this transient, which might damage the load? enter image description here

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    \$\begingroup\$ Are you sure about this? Authentic NE5532s require much more than 5V to operate effectively. Startup transient of the op-amp circuit sounds like the more pressing question, independent of whatever the power supply might be doing to it. \$\endgroup\$ Commented Oct 12, 2023 at 7:10

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How can I avoid this transient, which might damage the load?

The transient spike when enabling the LP2985-50 isn't expected behavior. To address this:

  1. Output Capacitor: Ensure you're using the recommended capacitor value as specified in the datasheet, placed close to the VOUT pin.

  2. Input Capacitor: Place it near the VIN pin to reduce transients.

  3. Load Transient: Ensure your op-amps don't have a rapid surge in current upon power-up.

  4. Enable Pin Soft Start: Consider adding a soft-start circuit to the Enable pin to mitigate spikes.

  5. Protection: Use a TVS diode at the regulator's output for over-voltage protection.

  6. Bypass Capacitors for Op-Amps: Place them close to the op-amps' power pins.

  7. Oscilloscope: Monitor both the input and output of the regulator during the transient to diagnose the root cause.

Adjusting your circuit based on these points should help reduce or eliminate the transient. Hope this helps :)

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