SLVSEQ0A May 2019 – March 2020 TPS54A24
PRODUCTION DATA.
The first step is to decide on a switching frequency for the converter. The TPS54A24 is capable of running from 200 kHz to 1.6 MHz. Typically the highest switching frequency possible is desired because it produces the smallest solution 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 trade off made with selecting a higher switching frequency is extra switching power loss, which hurt the converter’s efficiency.
The maximum switching frequency for a given application is limited by the minimum on-time of the converter and is estimated with Equation 13. Using a maximum minimum on-time of 150 ns for the TPS54A24 and 17 V maximum input voltage for this application, the maximum switching frequency is 706 kHz. The selected switching frequency must also consider the 10% tolerance of the switching frequency. A switching frequency of 500 kHz was selected for a good balance of solution size and efficiency. Equation 14 calculates R7 (RT) to be 97.6 kΩ. A standard 1% value of 100 kΩ was chosen in the design.
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