71M6541D Datasheet, PDF (19/166 Pages) Maxim Integrated Products – 0.1% Accuracy Over 2000:1 Current Range Energy Meter ICs

71M6541D/F/G and 71M6542F/G Data Sheet
Delay compensation and other functions in the CE code require the settings for MUX_DIV[3:0],
MUXx_SEL[3:0], RMT_E, FIR_LEN[1:0], ADC_DIV and PLL_FAST to be fixed for a given CE code.
Refer to Table 1 and Table 2 for the settings that are applicable to the 71M6541D/F/G and
71M6542F/G.
Table 4 summarizes the I/O RAM registers used for configuring the multiplexer, signals pins, and ADC.
All listed registers are 0 after reset and wake from battery modes, and are readable and writable.
Table 4: Multiplexer and ADC Configuration Bits
Name
Location Description
MUX0_SEL[3:0] 2105[3:0] Selects the ADC input converted during time slot 0.
MUX1_SEL[3:0] 2105[7:4] Selects the ADC input converted during time slot 1.
MUX2_SEL[3:0] 2104[3:0] Selects the ADC input converted during time slot 2.
MUX3_SEL[3:0] 2104[7:4] Selects the ADC input converted during time slot 3.
MUX4_SEL[3:0] 2103[3:0] Selects the ADC input converted during time slot 4.
MUX5_SEL[3:0] 2103[7:4] Selects the ADC input converted during time slot 5.
MUX6_SEL[3:0] 2102[3:0] Selects the ADC input converted during time slot 6.
MUX7_SEL[3:0] 2102[7:0] Selects the ADC input converted during time slot 7.
MUX8_SEL[3:0] 2101[3:0] Selects the ADC input converted during time slot 8.
MUX9_SEL[3:0] 2101[7:0] Selects the ADC input converted during time slot 9.
MUX10_SEL[3:0] 2100[3:0] Selects the ADC input converted during time slot 10.
ADC_DIV
2200[5] Controls the rate of the ADC and FIR clocks.
MUX_DIV[3:0] 2100[7:4] The number of ADC time slots in each multiplexer frame (maximum = 11).
PLL_FAST
FIR_LEN[1:0]
2200[4] Controls the speed of the PLL and MCK.
210C[1] ^{Determines the number of ADC cycles in the ADC decimation FIR filter.}
DIFFA_E
210C[4] Enables the differential configuration for analog input pins IAP-IAN.
DIFFB_E
210C[5] Enables the differential configuration for analog input pins IBP-IBN.
RMT_E
2709[3]
Enables the remote sensor interface transforming pins IBP-IBN into a
digital balanced differential pair for communications with the 71M6x01
sensor.
PRE_E
2704[5] Enables the 8x pre-amplifier.
Refer to Table 76 starting on page 111 for more complete details about these I/O RAM locations.
2.2.3 Delay Compensation
When measuring the energy of a phase (i.e., Wh and VARh) in a service, the voltage and current for that
phase must be sampled at the same instant. Otherwise, the phase difference, Ф, introduces errors.
φ
=
t_delay
T
⋅ 360^o
= t_delay
⋅
f
⋅ 360^o
Where f is the frequency of the input signal, T = 1/f and t_delay is the sampling delay between current and
voltage.
Traditionally, sampling is accomplished by using two A/D converters per phase (one for voltage and the
other one for current) controlled to sample simultaneously. Maxim’s Teridian Single-Converter
Technology, however, exploits the 32-bit signal processing capability of its CE to implement “constant
delay” all-pass filters. The all-pass filter corrects for the conversion time difference between the voltage
and the corresponding current samples that are obtained with a single multiplexed A/D converter.
The “constant delay” all-pass filter provides a broad-band delay 360^o – θ, which is precisely matched to
the difference in sample time between the voltage and the current of a given phase. This digital filter
does not affect the amplitude of the signal, but provides a precisely controlled phase response.
The recommended ADC multiplexer sequence samples the current first, immediately followed by
sampling of the corresponding phase voltage, thus the voltage is delayed by a phase angle Ф relative to