So while an injection network is needed for stability, it also adds impedance in series with inject capacitor, thus

compromising EMI mitigation. As shown below, the user can minimize the impact on performance with careful

and appropriate design.

Illustrated in Figure 9-4, at low frequencies in the range of 5 kHz to 50 kHz, components RD1 and CD2 provide

compensation and RD3 damps the effects of LC resonance. At higher frequencies (above 10 kHz), the dominant

component impedance of each branch transitions to enable better attenuation performance:

• RD1 transitions to CD1

• CD2 transitions to RD2

• RD3 transitions to CD3

Finally, CD1 transitions to RD1A if needed for phase margin of the AEF loop at high frequencies, typically above

100 kHz.

When viewed in a clockwise direction, Figure 9-4 shows these transitions in sequence as frequency increases.

CG1

IGND

VDD

INJ

EN

COMP1

SENSE1

SENSE3

COMP2

REFGND

CINJ

CD2

RD3

12 V

RD1

SENSE2

SENSE4

TPSF12C3

Low-frequency

equivalent circuit

RD3 in series with inject capacitor CINJ

provides damping at low frequency

RC filter (RD1, CD2) provides compensation

at low frequency for stability

RG

IGND

VDD

INJ

EN

COMP1

SENSE1

SENSE3

COMP2

REFGND

CINJ

CD1

CD2

RD3

12 V

SENSE2

SENSE4

TPSF12C3

Mid-frequency

equivalent circuit

The impedance of CD1 shunts that of RD1 as

frequency increases. Lower impedance in series

with CINJ helps AEF performance. CD2 > CD1

Increasing

frequency

RG

IGND

VDD

INJ

EN

COMP1

SENSE1

SENSE3

COMP2

REFGND

CINJ

CD1

12 V

SENSE2

SENSE4

TPSF12C3

High-frequency

equivalent circuit

As frequency increases, the impedance of CD3 shunts that

of RD3, which helps attenuation performance. CD3

CINJ

Increasing

frequency

CD3

RD2

IGND

VDD

INJ

EN

COMP1

SENSE1

SENSE3

COMP2

REFGND

CINJ

12 V

SENSE2

SENSE4

TPSF12C3

Highest-frequency

equivalent circuit

At high frequencies, the impedance of RD1A

exceeds that of CD1. RD1A provides damping and

improves the phase margin of the AEF loop

CD3

RD2

Increasing

frequency

RD1A

CG2

At higher frequency, the impedance of RD2 exceeds

that of CD2, resulting in RD2 and CD1 forming a high-

pass filter, which maximizes VINJD

VINJD

CSEN1–CSEN4

CSEN1–CSEN4

CSEN1–CSEN4

CSEN1–CSEN4

Figure 9-4. Dominant Components of the Injection Network vs Frequency

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TPSF12C3

SNVSCB8 – MARCH 2023

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