71M6521DE Datasheet, PDF (49/101 Pages) Teridian Semiconductor Corporation – Energy Meter IC

71M6521DE/71M6521FE
Energy Meter IC
DATASHEET
JANUARY 2008
CK32
MUX_SYNC
CKTEST
TMUXOUT/RTM
FLAG
RTMDATA0 (32 bits)
RTMDATA1 (32 bits)
RTMDATA2 (32 bits)
RTMDATA3 (32 bits)
0 1 30 31
FLAG
0 1 30 31
FLAG
0 1 30 31
FLAG
0 1 30 31
Figure 17: RTM Output Format
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 71M6521DE/FE 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 BROWNOUT mode (see Wake Up Behavior section). 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.
Meters that do not require functionality in the battery modes, e.g. meters 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, meters 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
pushbutton events. When the PB pin is pulled high (pushbutton is pressed), the IE_PB interrupt flag (SFR 0xE8[4]) is set, and
when the wake-up timer times out, the IE_WAKE interrupt flag (SFR 0xE8[5]) is set.
In the absence of system power, if the voltage margin for the LDO regulator providing 2.5V 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 3V to ensure
that BAT_OK remains true. Under this condition, the 71M6521DE/FE stays in SLEEP mode, even if the voltage margin for the
LDO improves (BAT_OK true).
Table 60 shows the circuit functions available in each operating mode.
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