| VREG, BOR, PORAlthough the core and I/O circuitry operate on two different voltages, these devices have an on-chipvoltage regulator (VREG) to generate the VDD voltage from the VDDIO supply. This eliminates the cost andspace of a second external regulator on an application board. Additionally, internal power-on reset (POR)and brown-out reset (BOR) circuits monitor both the VDD and VDDIO rails during power-up and run mode.2.8.1On-chip Voltage Regulator (VREG)A linear regulator generates the core voltage (VDD) from the VDDIO supply. Therefore, although capacitorsare required on each VDD pin to stabilize the generated voltage, power need not be supplied to these pinsto operate the device. Conversely, the VREG can be disabled, should power or redundancy be theprimary concern of the application.2.8.1.1Using the On-chip VREGTo utilize the on-chip VREG, the VREGENZ pin should be tied low and the appropriate recommendedoperating voltage should be supplied to the VDDIO and VDDA pins. In this case, the VDD voltage needed bythe core logic will be generated by the VREG. Each VDD pin requires on the order of 1.2 μF (minimum)capacitance for proper regulation of the VREG. These capacitors should be located as close as possibleto the VDD pins.2.8.1.2Disabling the On-chip VREGTo conserve power, it is also possible to disable the on-chip VREG and supply the core logic voltage tothe VDD pins with a more efficient external regulator. To enable this option, the VREGENZ pin must be tiedhig |
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