ISOW7721: The output ripple and noise of the isolated DC-to-DC converter

Edward Lee

Part Number: ISOW7721
Other Parts Discussed in Thread: ISO7721,

Dears,

I have questions regarding the output noise in the DC-to-DC converter of ISO7721. There is information about the output ripple on isolated supply (pk-pk).

My questions are

1. Is there any information about the total output noise? And what if we would like to reduce or suppress the noise, will a external LDO help a lot?

2. Is the frequency of the ripple about 25MHz? Do you have any captured waveforms (time domain or frequency domain) for us to reference?

Thank you for your response in advance

Best Regards

Edward

over 1 year ago

0 Edward Lee over 1 year ago

Prodigy 10 points

Sorry for the typo. Should be ISOW7721!

0 Michael J Schultis over 1 year ago in reply to Edward Lee

TI__Mastermind 24805 points

Hello Edward,

Please note that today is a holiday, and our experts will review and get back to you with a response tomorrow.

Best,

Michael

0 Edward Lee over 1 year ago in reply to Michael J Schultis

Prodigy 10 points

Hi Michael,

Thank you for the information. I found some ripple pictures in the datasheet.

The switching frequency seems to change with different output capacitors as well as the amplitude of the ripple.

Does this mean that the switching frequency of internal DC-to-DC is lower than 250KHz?

Thank you

Best Regards

Edward

0 Koteshwar Rao over 1 year ago in reply to Edward Lee

TI__Guru 53705 points

Hi Edward,

Thank you for reaching out, please see my inputs below.

Yes, LDO can help further reduce the output noise.
Like you have already found, the waveform are shown in datasheet. The ripple frequency is going to be same as device regulation / PWM frequency and that is what you are seeing in the waveform. The frequency also depends on the load, the frequency increases with higher loads while it decreases with lower loads.
1. Yes, higher decoupling capacitors reduces the ripple as you see in datasheet waveform. Higher cap also means higher load, this also leads to some increase in regulation / PWM frequency.

Regards,
Koteshwar Rao

0 Edward Lee over 1 year ago in reply to Koteshwar Rao

Prodigy 10 points

Hi Koteshwar,

Thank you for your inputs. That helps a lot.

Best Regards

Edward

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ISOW7721: The output ripple and noise of the isolated DC-to-DC converter