Texas Instruments TPSF12C1EVM-FILTER User Manual page 11

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2.5.1 AEF Circuit Optimization and Debug
Here are some considerations and best practices to optimize AEF circuit operation:
1. If the EMI measurement with AEF enabled is not performing as expected, probe the INJ pin voltage while
the regulator is switching. Verify that the INJ pin voltage is not getting clipped near the positive or negative
supply rails, as mentioned in step 2 of
• If the INJ pin voltage is getting clipped, increase the regulator-side Y-capacitance and/or the inject
capacitance. Then recheck the loop stability using the TPSF12C1
2. The metallic chassis structure is a critical part of the overall filter implementation. The filter PCB typically
mounts to the chassis structure using several screw attachments, and the chassis serves to connect the
various GND nodes on the filter PCB. These nodes are not explicitly connected with copper on the PCB and
instead rely on the chassis to complete the electrical connection. As such, the chassis becomes the lowest
impedance return path for CM noise current.
• When testing a power stage that includes a chassis as illustrated in
couple to the reference ground plane of the EMI measurement setup and thus bypass a filter circuit
that is not closely referenced to this ground plane. In this case, TI recommends bonding the GND plane
copper of the filter EVM directly to the reference ground plane. This also serves to minimize parasitic
inductance in the GND connection to the AEF circuit. CM current emanating from the power stage then
gets recirculated by the low shunt impedance of the filter Y-capacitors (both active and passive), thus
preventing noise from reaching the LISN.
3. Based on the amplification of the effective Y-capacitance, AEF allows reduction of the CM choke inductance
while maintaining the same LC corner frequency and CM attenuation characteristic. However, a choke with
reduced CM inductance and smaller size normally has a lower leakage inductance, which is responsible for
DM attenuation along with the X-capacitors.
• If the DM inductance is significantly reduced with the smaller CM chokes, then increase the X
capacitance or add a small discrete inductor to obtain sufficient DM attenuation. Otherwise, a high DM
noise component (relative to the CM component) can dominate the total noise measurement, therefore
concealing the impact of AEF on CM noise mitigation.
4. Typical values for the sense and inject capacitances are 680 pF and 4.7 nF, respectively. Depending on the
final implementation in the target application, the default damping and compensation component values
installed on the EVM can require modification by the user to achieve acceptable loop stability. Ferrite
chokes are inherently more difficult to stabilize than their nanocrystalline equivalents.
• For additional context pertaining to component selection and circuit optimization, refer to the
product data sheet and the TPSF12C1
SLVUCQ2A – JULY 2023 – REVISED JULY 2023
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Section 2.4.
quickstart calculator.
Active EMI Filter Evaluation Module for Single-Phase AC Power Systems
Copyright © 2023 Texas Instruments Incorporated
quickstart calculator or by simulation.
Figure 2-2, CM noise can capacitively
Hardware
TPSF12C1
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