INN3977CQ load transient response
Hi,
1) I got more ringing at output of INN3977CQ circuit during load transient. How to reduce ringing in the load transient conditions.
2) How to update the design as INN3977CQ is integrated device if any phase/gain margin improvement findings in Bode plot during testing. Can you share reference bode plot for INN3977CQ design.
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Load transient waveform is attached. In load transient, output voltage is withing 10% regulation an settling time.
Could you provide details how the ringing during load step change causes phase margin and how ringing output affects or methods to reduce output ringing in INN3977CQ based design.
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| INN3977CQ load transient.jpg (147.18 KB) | 147.18 KB |
Hi Manju H,
Based on your image, the output voltage is even in 5% tolerance range, which is a good indication that the feedback is quite stable. Please correct me if my understanding is wrong, but I believe that you're currently simulating using SIMETRIX, right?
To improve the transient response of the InnoSwitch3 devices, implementing an RC feedforward circuit across the upper feedback resistor with a starting value of 10 kΩ and 10 nF is suggested. Then adjusting their value may be necessary as needed. Please refer to the highlighted component on the image attached.
If you want to have a tighter output voltage tolerance, I recommend adding the "Precision Voltage Regulation" circuit on the design. Please refer to the other attached image. This can be found as well on page 45 of the InnoSwitch3-AQ design guide (AN-106).
Feel free to reach out again if you have any further questions or clarifications.
Regards,
Tommy
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| Precision voltage regulation.png (219.31 KB) | 219.31 KB |
I am using simplis simulation tool for which device circuit is simulated. I changed to 22k, 33nF in feedforward RC values and observed no change in ringing in the output ripple. any suggested value for this RC feedforward components or any application note details
Hello Manju H,
You can try increasing the value of the feedforward capacitor up to 100 nF and observe if there will be change on the ringing. Adding an additional SMD ceramic capacitor (10 nF to 1 uF) directly at the output voltage terminals can help reduce the ringing.
However, since the InnoSwitch3 devices has an ON/OFF control mechanism, the ringing will not be completely eliminated. As long as the regulation during transient loading is still within the required tolerance, it should be okay. Seeing that your current simulation is within 5% tolerance, the design should be okay. The main purpose of the RC feedforward circuit is to helps speed up the feedback response of the InnoSwitch3 devices. However, the ringing would remain as is. You can refer to the transient loading waveforms of some of our reference designs that is mentioned below that the ringing is still there.
Regards,
Tommy
Hello Manju H,
Good day and thank you for choosing Power Integrations.
Can you share your schematic diagram and some waveforms regarding the ringing on the output that you're referring to?
To answer question number 2, the Bode plot only applies to linear systems, which include PWM control. Our InnoSwitch3 IC uses an ON/OFF control mechanism, which is a non-linear control, to regulate the output voltage. So, we don't have any bode plot reference for our InnoSwitch3 ICs.
To check the stability of the design that uses InnoSwitch3 ICs, you can check the output voltage ripple, output voltage regulation, and transient response of the design. All should be within the specified tolerance of the design.
I will wait for your response regarding the ringing in the load transient. Have a nice day!
Regards,
Tommy