ZHCSCK0C June 2014 – September 2021 TPS55340-Q1
PRODUCTION DATA
This design was compensated by measuring the frequency response of the power stage at the lowest input voltage of 6 V and choosing the components for the desired bandwidth. The lowest right-half plane zero (ƒ(RHPZ)) is calculated with Equation 54 to be 36.7 kHz. When using the recommendation of limiting the bandwidth to 1/3 of ƒ(RHPZ) or less, the recommended maximum bandwidth is 12.2 kHz.
This design also uses only one pole and one zero. To achieve approximately 60 degrees of phase margin, the power stage phase must be no lower than approximately –120 degrees at the desired bandwidth. To ensure a stable design, R3 was initially set to 1 kΩ and C4 was set to 1 µF. Figure 8-11 shows the measurement of the power stage. At 7 kHz, the power stage has a gain of 19.52 dB and phase of –118.1 degrees.
Because no changes occur in the transconductance amplifier, the equations used to calculate the external compensation components in a boost design can be used in the SEPIC design. Using the maximum gm(ea) from the electrical specification of 440 µmho, Equation 40 calculates the nearest standard value of R3 to be 2.37 kΩ. Using Equation 41, C4 is calculated to the nearest standard value of 0.1 µF.