DS_6612_001
78M6612 Data Sheet
2.3 Battery Modes
Shortly after system power (V3P3SYS) is applied, the part will be in MISSION mode. MISSION mode
means that the part is operating with system power and that the internal PLL is stable. This mode is the
normal operation mode where the part is capable of measuring energy.
When system power is not available (i.e. when V1<VBIAS), the 78M6612 can be in one of three battery
modes, i.e. BROWNOUT, LCD, or SLEEP mode. As soon as V1 falls below VBIAS or when the part
wakes up under battery power (with sufficient voltage margin), the part will automatically enter BROWN-
OUT mode (see Section 2.5 Wake Up Behavior). From BROWNOUT mode, the MPU may enter either
LCD mode or SLEEP mode by setting either the LCD_ONLY or SLEEP I/O RAM bits (only one bit can be
set at the same time in BROWNOUT mode, since setting one bit will already force the part into SLEEP or
LCD mode, disabling the MPU).
Figure 18 shows a state diagram of the various operation modes, with the possible transitions between
modes. For information on the timing of mode transitions refer to Figure 22 through Figure 24.
Power and Energy Measurement devices that do not require functionality in the battery
modes, e.g. Power and Energy Measurement devices that only use the SLEEP mode to
maintain the RTC, still need to contain code that brings the chip from BROWNOUT mode
to SLEEP mode. Otherwise, the chip remains in BROWNOUT mode, once the system power is
missing, and consumes more current than intended.
Similarly, Power and Energy Measurement devices equipped with batteries need to
contain code that transitions the chip to SLEEP mode as soon as the battery is attached
in production. Otherwise, remaining in BROWNOUT mode would add unnecessary drain
to the battery.
The transition from MISSION mode to BROWNOUT mode is signaled by the IE_PLLFALL interrupt flag
(in SFR 0xE8[7]). The transition in the other direction is signaled by the IE_PLLRISE interrupt flag (SFR
0xE8[6]), when the PLL becomes stable.
Transitions from both LCD and SLEEP mode back to BROWNOUT mode are initiated by wake-up timer
timeout conditions or wake-up pin events.
In the absence of system power, if the voltage margin for the LDO regulator providing 2.5 V to the internal
circuitry becomes too low to be safe, the part automatically enters sleep mode (BAT_OK false). The
battery voltage must stay above 3 V to ensure that BAT_OK remains true. Under this condition, the
78M6612 stays in SLEEP mode, even if the voltage margin for the LDO improves (BAT_OK true).
Table 44 shows the circuit functions available in each operating mode.
Rev. 1.2
53
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
