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MC9S12ZVC MCU with On-chip regulator, VDDX and VDDA supply

Question asked by Rakshith Manjunath on Nov 30, 2018
Latest reply on Dec 5, 2018 by RADEK SESTAK

MC9S12ZVC has a on-chip voltage regulator with ballast pins BCTL and BCTLC which supply base current to the ballast transistor to get VDDX, VDDA and VDDC. The reference design uses a 5.6V zener diode at the VDDX and VDDA but the data sheet says it is a 5V input. If they are generated by the on-chip regulator why use a 5.6V zener at VDDX and VDDA? I have attached the screenshot of the schematic below.

 

Please Advice.Thank you!

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