SLVSIN8 Data sheet

SLVSIN8 June 2026 TPSM65660

ADVMIX

8.1.2 Error Amplifier and Compensation

Figure 8-2 shows a Type-ll compensator using a transconductance error amplifier (EA). The dominant pole of the EA open-loop gain is set by the EA output resistance, R_OEA, and effective bandwidth-limiting capacitance, C_BW, as shown by Equation 18.

Equation 18.

G_{E A (o p e n l o o p)} (s) = - \frac{g_{m} \times R_{O E A}}{1 + s \times R_{O E A} \times C_{B W}}

The EA high-frequency pole is neglected in the above expression. Equation 19 expresses the compensator transfer function from output voltage to COMP, including the gain contribution from the feedback divider.

Equation 19.

G_{c} (s) = \frac{{\hat{v}}_{c} (s)}{{\hat{v}}_{o u t} (s)} = - \frac{V_{R E F}}{V_{O U T}} \times \frac{g_{m} \times R_{O E A} \times (1 + \frac{s}{ω_{z 1}})}{(1 + \frac{s}{ω_{p 1}}) \times (1 + \frac{s}{ω_{p 2}})}

where

V_REF is the feedback voltage reference
g_m is the EA transconductance
R_OEA is the EA output impedance

Equation 20.

ω_{z 1} = \frac{1}{R_{C O M P} \times C_{C O M P}}

Equation 21.

ω_{p 1} = \frac{1}{R_{O E A} \times (C_{C O M P} + C_{H F} + C_{B W})} ≅ \frac{1}{R_{O E A} \times C_{C O M P}}

Equation 22.

ω_{p 2} = \frac{1}{R_{C O M P} \times (C_{C O M P} | | (C_{H F} + C_{B W}))} ≅ \frac{1}{R_{C O M P} \times C_{H F}}

The EA compensation components create a pole close to the origin, a zero, and a high-frequency pole. Typically, R_COMP << R_OEA and C_COMP >> C_BW and C_HF, so the approximations are valid. Figure 8-2 circles the poles in red and the zero in blue.

TPSM65660 Error
Amplifier and Compensation Network

Figure 8-2 Error Amplifier and Compensation Network