SNOSDL9 Data sheet

SNOSDL9B December 2024 – May 2026 LMG5126

PRODUCTION DATA

7.2.3.19 Loop Compensation

R_COMP, C_COMP and C_HF configure the error amplifier gain and phase characteristics to produce a stable voltage loop. For a quick start, follow the following four steps:

Select crossover frequency, f_C. Select the cross over frequency (f_C) at one fifth of the RHPZ frequency or one tenth of the switching frequency whichever is lower. Choose RHPZ with minimum input voltage and maximum output voltage.
Equation 90. $\frac{f_{s w}}{10} = 40 k H z$
Equation 91. $\frac{f_{R H P Z}}{5} = \frac{R_{o u t} \times {D'}^{2}}{{5 \times 2 π \times L}_{m_e q}} = 1.9 k H z$
Crossover frequency f_c=1.9kHz is selected.
Determine required R_COMP
Knowing f_c, R_COMP is calculated as follows:
Equation 92. $R_{COMP} = \frac{2 π \times f_{c} \times C_{out} \times A_{cs} \times R_{cs_eq}}{D' \times K_{FB} \times g_{m} {\times G}_{ACB} (2 π \times f_{c})} = \frac{2 π \times 1.9 kHz \times 700 μF \times 10 \times 2 mΩ}{0.2 \times \frac{1}{30} \times 1 \frac{mA}{V} \times \frac{1}{2}} = 50.1 kΩ$
A standard value of 50kΩ is selected for R_COMP
Determine C_COMP
Place ω_{Z_EA} at the load pole frequency ω_{P_LF} to cancel load pole. Knowing R_COMP, C_COMP is calculated as follows:
Equation 93. $C_{C O M P} = \frac{1}{R_{C O M P} \times ω_{P_L F}} = \frac{1}{50 k Ω \times \frac{2}{5 Ω 700 μ F}} = 35 n F$
A standard value of 35nF is selected for C_COMP
Determine C_HF.
Place ω_HF at ω_RHPZ or ω_{Z_ESR} zero whichever is lower. Knowing R_COMP, RHPZ and ESR zero, C_HF is calculated as follows:
Equation 94. $C_{HF} = \frac{1}{R_{COMP} \times ω_{HF}} = \frac{1}{50 kΩ \times 9.5 kHz} = 2 nF$
A standard value of 2.2nF is selected for C_HF.