to further reject line-frequency components appearing at the INJ output. Capacitor CG2 preserves gain at high

frequencies, which extends the AEF bandwidth.

Choose a value for RG between 1 kΩ and 2 kΩ. A resistance of 1.5 kΩ is a common choice and selected in this

example to set a midband gain of 50 dB. Choose capacitances for CG1 and CG2 of 10 nF and 10 pF, respectively,

which establishes a gain rolloff below approximately 10 kHz for line-and low-frequency attenuation.

9.2.1.2.4 Injection Network

The components connected between the INJ pin and inject capacitor establish a damped injection network.

Damping is specifically required to manage resonance between the CM choke inductance and inject

capacitance, which manifests in the AEF loop gain as a pair of complex zeros.

Figure 9-3 highlights three specific RC branches: RD1, RD1A and CD1 form one branch from the INJ pin; RD2 and

CD2 in series connect to GND; RD3 and CD3 in parallel connect to the inject capacitor.

Chassis (PE)

RG

CG1

IGND

VDD

INJ

EN

COMP1

SENSE1

SENSE3

COMP2

REFGND

CINJ

CG2

CD1

RD2

CD2

RD3

CD3

CVDD

12 V

RD1

RD1A

SENSE2

SENSE4

TPSF12C3

= ZD1 branch

= ZD2 branch

DINJ

U1

= ZD3 branch

ZD1

ZD3

ZD2

3-phase

AC source

AC/DC

regulator

Chassis

L1

L2

L3

N

CSEN1–CSEN4

CY1–CY4

CX7–CX9

LCM2-AEF

LCM1-AEF

CX4–CX6

CX1–CX3

Figure 9-3. Injection Network

Based on the sensing and injection mechanism, the AEF circuit presents a very low impedance to CM noise.

Given the three damping impedance branches highlighted in Figure 9-3, Equation 1 approximates the AEF

impedance as:

(1)

where the term GAEF is the gain from the power lines to the INJ node (see the TPSF12C3 quickstart calculator

for related detail).

Equation 1 shows that the impedance ZINJ appears in series with ZD3 and a parallel combination of ZD1 and ZD2.

Furthermore, the gain GAEF is reduced by the voltage divider ratio between ZD2 and ZD1. These effects combine

to increase the effective impedance of the AEF and hence reduce its attenuation performance, thus illustrating a

trade-off between performance and stability.

TPSF12C3

SNVSCB8 – MARCH 2023

www.ti.com

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