With Discrete solution, make sure to have following criteria met to ensure ASIL-B requirement.

1. System power requirements

   This is one of the important steps when we want to design a power supply and monitoring solution for the MCU and the rest of the system. Calculate the maximum current consumption value of IDD and IDDIO for MCU from its data sheet and include all the current consumption of other components on each rail.

2. Selection of LDO /Buck converters
   1. When selecting an LDO as a power supply for VDD and VDDIO, make sure they are functional safety capable, auto qualified and have good accuracy (1% or better is recommended)
   2. When selecting a Buck converter as a power supply for VDD or VDDIO, make sure they are functional safety capable and auto qualified
   3. When selecting a Dual Buck converter as a power supply for VDD or VDDIO, make sure they are functional safety capable and auto qualified
   4. To choose the appropriate regulator for specific applications, parameters such as the input voltage, required output voltage, maximum load current, size, efficiency, frequency and power rating need to be considered to maximize regulator characteristics. If efficiency is not your priority, heat is not a concern, the current necessary is very small, or Vin is only slightly higher than Vout, an LDO can be used. But, if efficiency and performance are your utmost concern even if it is more complex and likely to be more expensive, then a buck converter is the ideal choice.

      As for electrical noise, LDOs can reach a lower noise floor than buck converters. This is because buck converters (and other switching power supplies) use inductors that have the tendency to produce significant noise.

3. Selection of monitors

   Select an IC that can monitor VDD and VDDIO Supply rails. Use either the single Multichannel Supervisor or separate supervisor for each of the power rails. Select ICs that are functional safety complaint and auto qualified. For the monitoring of VDD, see the device-specific data sheet.

4. Selection of external VREF for ADC

   Make sure IC selected is functional safety capable and auto qualified.

   VREF can be supplied externally or internally. Using the internal reference for the ADC provides better accuracy compared to an external reference using a supply rail. If external VREF is used, use the buffer to minimize the noise on the rail. Based on the functional safety goals of the application, voltage monitoring of ADC VREF may be required.

5. Selection of Watchdog

   You can use an external watchdog or supervisor with integrated window/Q&A watchdog.

   Figure 2-3 ASILB: MCU With External VREFHI and External VREG
   Figure 2-4 ASILB: MCU With Internal VREFHI and External VREG