S32K314 1V5 Core supply

[ajnas-c]

Hi,

Currently, we're engaged in a project involving the S32K314 microcontroller. The recommended configuration for the core of the controller is a supply voltage of 1.5V, as indicated by the reference design. We have implemented the Ballast transistor circuit to achieve this 1.5V core supply. However, upon enabling the VRCCTRL pin in the code, the circuit does not appear to be delivering the expected 1.5V output. Interestingly, even without this 1.5V supply, the controller continues to operate.

This prompts the question: is the 1.5V supply truly necessary for the controller to function optimally? If it's determined that the 1.5V supply is not essential, could we potentially consider removing the Ballast transistor circuit? Any insights on this matter would be greatly appreciated. Your input is welcome.

Regards,

Ajnas C

[danielmartynek]

Hi @ajnas-c,

Out of reset, the internal V11 is generated from VDD_HV_A by the internal Boot regulator.

Because CONFIG[LMAUTOEN] = 1 by default, the regulator switches to the V15 regulator (last mile) automatically as soon as the V15 voltage reaches 1.42V.

If you use the ballast transistor configuration, you need to enable the control base pin PMC_CONFIG[LMBCTLEN].

The V15 last mile regulator is necessary if the PLL is used (LMEN must be set before the PLL is enabled), otherwise, it is not necessary.

Regards,

Daniel

[ajnas-c]

Thanks Daniel.

Will the performance of the controller be affected if we remove the 1V5 circuit?

Additionally, is the external 16MHz crystal necessary for the S32K314? Can the crystal be removed?

We have examined the clock frequency using a DSO but have not observed any oscillations.

[danielmartynek]

As I said, the V15 domain is necessary if the PLL is used.

The external FXOSC is not necessary, the MCU can run from the internal FIRC.

Please have a look at the DS rev.7, Table 16. Low speed RUN mode supply currents.

However, the FIRC oscillator is not very precise for applications that need the precision e.g. for FlexCAN.

Regards,

Daniel