JAJSPW0B June 2023 – June 2024 TPS543B25T
PRODUCTION DATA
The first step is to decide on a switching frequency. The TPS543B25T can operate at five different frequencies from 500kHz to 2.2MHz. fSW is set by the resistor value from the FSEL pin to ground. Typically, the highest switching frequency possible is desired because the highest switching frequency produces the smallest design size. A high switching frequency allows for smaller inductors and output capacitors compared to a power supply that switches at a lower frequency. The main tradeoff made with selecting a higher switching frequency is extra switching power loss, which hurts the efficiency of the regulator.
The maximum switching frequency for a given application can be limited by the minimum on time of the regulator and the maximum fSW can be estimated with Equation 15. Using the maximum minimum on time of 40ns and 18.0V maximum input voltage for this application, the maximum switching frequency is 1389kHz. The selected switching frequency must also consider the tolerance of the switching frequency. A switching frequency of 1000kHz was selected for a good balance of design size and efficiency. To set the frequency to 1000kHz the selected FSEL resistor is 11.8kΩ per Table 6-1.
Figure 7-2 shows the maximum recommended input voltage versus output voltage for each FSEL frequency. This graph uses the maximum minimum on time of 40ns and includes 10% tolerance on the switching frequency.