Input Capacitance - Buck1, Buck2, Buck3

Each of the Buck converters require an input capacitor on the corresponding PVIN_Bx pin. The capacitor value must be selected taking into account the voltage and temperature de-rating. Due to the nature of the switching converter, a low ESR ceramic capacitor is required for best input voltage filtering. The typical recommended capacitance is 4.7 uF, 10V capacitor. Higher input capacitance can be used if the PCB size allows larger footprint.

Output Capacitance - Buck1, Buck2, Buck3

Every Buck output requires a local output capacitor to form the capacitive part of the LC output filter. Ceramic capacitor with X7 temperature coefficient are recommended. Non-automotive applications can use X6 or lower based on the operating temperature. The Buck converters have multiple switching modes and bandwidth configuration that impact the output capacitor selection. The switching mode configuration (BUCK_FF_ENABLE) is a global register field that applies to the three Buck converters and must not be changed at any point. The bandwidth selection is an independent register field for each Buck converter. Refer to the Technical Reference Manual (TRM) for the specific orderable part number to identify the NVM configuration and the corresponding output capacitance requirements. Table Table 8-1 shows the required minimum and maximum capacitance (after derating) for each switching mode and bandwidth configuration. DC bias voltage characteristics of ceramic capacitors, tolerance, aging and temperature effects must be considered. ESR must be 10 mΩ or lower.

Inductor Selection - Buck1, Buck2, Buck3

Internal parameters for the buck converters are optimized for 0.47uF inductor. DCR must be 50 mΩ or lower. Ensure that the selected inductor is rated to support saturation current of at least 7.4A for Buck1 and 5.4A for Buck2/Buck3.