71M6521DEIM-DB Maxim Integrated Products, 71M6521DEIM-DB Datasheet - Page 68

• Manufacturer Part Number: 71M6521DEIM-DB
• Description: Power Management Modules & Development Tools 71M6521DE DEMO BOARD M6521DE DEMO BOARD
• Manufacturer: Maxim Integrated Products

Specifications of 71M6521DEIM-DB

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

initialized when Brownout mode is entered from a state where the chip is powered down (if Brownout mode is entered
from Mission mode, the I/O pins are properly initialized, and the chip will enter Sleep mode automatically causing much
lower supply current into the VBAT).
The ADC collects data from the electrical inputs on a cycle that repeats at 2520Hz. On each ADC cycle, the compute
engine (CE) code digitally filters and adjusts the data using gain parameters (CAL_Ix, CAL_Vx) and phase adjustment
parameters (PHADJ_x).
Normally, a calibration operation during manufacturing defines these adjustments and stores them in flash or EEPROM
to be placed into CE memory by the MPU when the meter powers up. The Demo Code includes a basic linear self-
calibration function that can typically reach 0.05% accuracy. (meter.c: meter_run(), calphased.c: cal_begin(),
calibration() ).
Better calibration schemes are possible. The calibration save and restore operations (cal_save() and cal_restore() )
save and restore all adjustment variables, such as the constants for the real-time clock, not just the ones for electrical
measurements.
On each ADC cycle, 2520 times per second, the CE performs the following tasks:
On each ADC cycle, an MPU interrupt, "ce_busy" (see ce.c, ce_busyz_isr() ) is generated. Normally, the interrupt
service routine checks the CE's status word for the sag detection bits, and begins sag logic processing if a sag of the
line voltage is detected.
In the event of a sag detection (announcing a momentary brownout condition or even a blackout), the cumulative
quantities in memory are written to the EEPROM.
By the end of each accumulation interval, each second on the Demo Code, the CE performs the following tasks:
The CE code (see ce652x.c for a “C” image) digitally filters out the line frequency component of the signals, eliminating
any long-term inaccuracy caused by heterodyning between the line frequency and the sampling or calculation rates.
This also permits a meter to be used at 50 or 60Hz, or with inaccurate line frequencies.
Each metering equation has a CE code written for that calculation, so that the 6521 can calculate according to the most
common metering methods.
Once per accumulation interval, the MPU requests the CE code to make an alternative measurement (alternate
multiplexer cycle).
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It calculates intermediate results for that set of samples.
It runs a debounced check for sagging mains, with a configurable debounce function.
It has three equally-spaced opportunities to pulse each pulse output.
It calculates deviation from nominal calibration temperature (TEMP_X).
It calculates the frequency on a particular phase (FREQ_X).
It calculates watt hours (Wh) for each conductor, and the meter (WxSUM_X).
It calculates var hours (VARh) for each phase and the meter (VARxSUM_X).
It calculates summed squares of currents for each phase (IxSQSUM_X).
It calculates summed squares of voltages for each phase (VxSQSUM_X).
It counts zero crossings on the same phase as the frequency (MAINEDGE_X).
In general, to work in an operational meter (not a demo meter), the firmware has to be written to
handle the case of connecting a battery to a powered-down board (since in a factory setting,
batteries will most likely be added to meter boards that are powered down). The firmware must
immediately enter sleep mode in this situation.
Precautions when adding a battery: When a battery or other DC supply is added to a Demo Board that is
powered down, the 71M6521 Demo Code will cause the chip to enter Brownout mode and stay in Brownout
mode. It is possible that the VBAT pins of the chip draws up to 1mA in this state, since the I/O pins are not
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