78M6610+LMU Data Sheet
Data Refresh Rates
Instantaneous Voltage, Current, Power, and Quadrature measurement results are updated at the sample
rate of 4kS/s and are generally not useful unless accessed with a high speed interface such as SPI. The
CYCLE register is a 24-bit counter that increments every high-rate sample update and resets when low-
rate results are updated.
Low-rate results, updated at a user configurable rate, are typically used and more suitable for most
applications. The FRAME register is a counter that increments every accumulation interval. A data ready
indicator in the STATUS register indicates when new data is available.
The high-rate samples are averaged to produce one low-rate result (known as an accumulation interval),
increasing their accuracy and repeatability. Low-rate results include RMS voltages and currents,
frequency, power, energy, and power factor. The accumulation interval can be based on a fixed number
of ADC samples or locked to the incoming line voltage cycles.
If Line Lock is disabled, the accumulation interval defaults to a fixed time interval defined by the number
of samples defined in the SAMPLES register (default of 400 samples or 0.1 seconds).
When the Line-Lock bit in the Command Register is set, and a valid AC voltage signal is present, the
actual accumulation interval is stretched to the next positive zero crossing of the reference line voltage
after the defined number of samples has been reached. If there is not a valid AC signal present and line
lock is enabled, there is a 100 sample timeout implemented that would limit the accumulation interval to
SAMPLES+100.
The DIVISOR register records the actual duration (number of high-rate samples) of the last low-rate
interval whether or not Line-Lock is enabled.
Two bits in the CONFIG register allow the user to select the reference voltage slot for deriving zero-
crossing detection and line frequency.
CONFIG[23:22]
00
01
10
11
Voltage reference
S0
S2
S0-S2
S0+S2
Scaling Registers
Most measurement data is reported in binary full-scale units with a value range of -1.0 to 1 - LSB. All full
scale register readings correspond to the max analog input of 250mVpk (or 31.25mVpk with 8x gain). As
an example, if 230V-peak at the input to the voltage divider gives 250mV-peak at the chip input, one
would get a full scale register reading of 1 - LSB (0x7FFFFF) for instantaneous voltage. Similarly, if 30Apk
at the sensor input provides 250mV-peak to the chip input, a full scale register value of 1 - LSB
(0x7FFFFF) for instantaneous current would correspond to 30 amps. Full scale watts correspond to the
result of full scale current and voltage so, in this example, full scale watts is 230 x 30 or 6900 watts.
Nonvolatile registers (IFSCALE and VFSCALE) are provided for storing the real-world current and voltage
levels that apply to the full scale register readings for any given board design. Any host application can
then format the measurement results to any data format as needed. The usage of these nonvolatile
scratchpad registers is user defined and their content has no effect on the internal operations of the
device.
Frequency data has a range of 0 to +32768Hz less one LSB (format S15.8). Temperature data has a
fixed scaling with a range of -65536°C to +65536°C less one LSB (format S16.7).Energy data scaling is
described in detail in section 2.10.
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Rev 0
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
