3 VBAT Overview

The PIC16(L)F19197 family of devices come equipped with a VBAT pin that provides users with the ability to use an external backup power source to ensure that the SOSC and RTCC modules continue running if the VDD supply voltage were to fail. Utilizing the VBAT functionality of the module can be beneficial in applications that use the RTCC module, by helping to ensure that the time keeping values are retained when the VDD power supply is lost. The VBAT hardware determines when the VDD power supply to the RTCC and SOSC modules are no longer sufficient. When the supply drops below the required VDD voltage level, the RTCC and SOSC modules will automatically switch their supply voltage to run from the available VBAT power supply.

The RTCC and SOSC modules were designed with low power consumption in mind to help prolong battery life. The VBATBOR and BOR bits of the Power Control register set (PCONx) can be used to indicate whether a Brown-out Reset (BOR) occurred and to determine if a VBAT Brown-out Reset occurred, specifically. Table 3-1 summarizes the behavior that the PIC microcontroller will inhibit in the event of a Brown-out Reset when VBAT is utilized as a battery backup.

Table 3-1. VDD Vs. VBAT Switching
VDD StatusVBAT StatusDescription
VDD>VBORVBAT>VBORAll peripherals will operate from VDD. RTCC and SOSC modules will run from VBAT, if VBAT is greater than VDD. VBATBOR bit remains unchanged. BOR bit remains unchanged.
VDD>VBORVBAT<VBORAll peripherals will operate from VDD. VBATBOR bit remains unchanged. BOR bit remains unchanged.
VDD<VBORVBAT>VBORRTCC and SOSC will operate from VBAT while all other peripherals are held in a Reset state until VDD power supply is restored. VBATBOR bit remains unchanged. BOR bit is cleared to indicate Brown-out Reset
VDD<VBORVBAT<VBORAll peripherals (Including RTCC and SOSC) are held in a Reset state until a sufficient VDD or VBAT power supply is detected. VBATBOR bit cleared to indicate a Brown-out Reset. BOR bit is cleared to indicate Brown-out Reset.