LM25149: LM25149 AEF

Hi Eric, I will see if I can find someone to help with the explanation.

Hi Eric,

The AEF circuit detects the superimposed AC ripple on the VIN line and will sink/source current that is out of phase with the AC ripple (noise source) to reduce the conducted emissions. If the AC ripple going to the AEF is too large, the output of the AEF may saturate or clip because the bias rail voltage may not be high enough to allow the INJ pin to swing rail-to-rail (AEFVDD to AVSS). Think of AEF is like an op-amp. To keep the output from clipping or saturating, one can increase the voltage to the AEF (AEFVDD), limit the AC ripple input swing or decrease the gain of the ACS. 

The explanation that you gave is correct.

Ben

Hi Ben , 

Many thanks for your explanation.

Let me summary for this, so the railing is the same as saturation cause by ACS.

One more question, have we tested this , this AEF will have how much benefits compared to traditional LC filter

Hi Ben

 Sincere thanks for your support

Hi Eric,

Thank you and glad to be of help! :-)

Ben

Hi Ben，

How can I connect to you？ what’s your webex account?

Hi Ben,

in my attached images ,what's the ACS stands for ?  AC source?

Hi Eric,

ACS means "Air-core Coil Stage"

Ben 

Hi Ben, 

Do you means the ACS will generate a AC ripple for the Vbatt

BR

Eric

Hi Eric,

The ACS is the EMI filter stage that contains the chokes, X-capacitors and Y-capacitors.

Ben

Hi Eric,

A colleague of mine mentioned that the acronym "ACS" used in the slide above actually meant AC superimposed noise from the alternator. My apologies for misleading you.

Ben 

Hi Ben,

No worries

thanks for your support.

Thanks Eric. Glad to be of help.

Ben

Hi Ben, 

one more question, for the AEF ,how did it eliminate the specific frequency noise to reduce the EMI? cause you know, the inverter just make the output signal have 180 degree phase difference, from my side , I think the output of the inverter should have the same amplitude as the ACS, then this two signal will cancel each other out. then for the Vbatt, it seems no AC noise, but How can we sure our AEF will have unit gain in specific frequency? with the compensated resistor and capacitor?

Hi Eric,

The AEF is an analog filter so there is a specific frequency range where it reduces the EMI noise. Usually that frequency range is focused on the fundamental switching frequency and its subsequent harmonics.  The technical article:

https://www.ti.com/lit/ta/sszt179/sszt179.pdf

discusses about how AEF reduces EMI noise.

Ben

Ben C said:

technical article

Very thanks ，Ben

No problem Eric.

Ben