71M6543F/H and 71M6543G/GH Data Sheet
number of LCD segments and DIO pins can be implemented in software to accommodate various
requirements.
In addition to the temperature-trimmed ultra-precision voltage reference, the on-chip digital temperature
compensation mechanism includes a temperature sensor and associated controls for correction of unwanted
temperature effects on metrology and RTC accuracy (i.e., to meet the requirements of ANSI and IEC
standards). Temperature-dependent external components such as the crystal oscillator, current
transformers (CTs), Current Shunts and their corresponding signal conditioning circuits can be character-
ized and their correction factors can be programmed to produce electricity meters with exceptional accuracy
over the industrial temperature range.
One of the two internal UARTs is adapted to support an Infrared LED with internal drive and sense
configuration and can also function as a standard UART. The optical output can be modulated at 38 kHz.
This flexibility makes it possible to implement AMR meters with an IR interface. A block diagram of the IC
is shown in Figure 1.
2.2
Analog Front-End (AFE)
The AFE functions as a data acquisition system, controlled by the MPU. The 71M6543 AFE may also be
augmented by isolated 71M6xx3 sensors in order to support low-cost current shunt sensors. Figure 2,
and Figure 3 show the two most common configurations; other configurations are possible. Sensors that
are connected directly to the 71M6543 (i.e., IADC0-IADC1, VADC8, VADC9 and VADC10) are
multiplexed into the single second-order sigma-delta ADC input for sampling in the 71M6543. The
71M6543 ADC output is decimated by the FIR filter and stored in CE RAM where it can be accessed and
processed by the CE.
Shunt current sensors that are isolated by using a 71M6xx3 device, are sampled by a second-order
sigma delta ADC in the 71M6xx3 and the signal samples are transferred over the digital isolation interface
through the low-cost isolation pulse transformer.
Figure 2 shows the 71M6543 using shunt current sensors and the 71M6xx3 isolated sensor devices.
Figure 2 supports neutral current measurement with a local shunt connected to the IADC0-IADC1 input
plus three remote (isolated) shunt sensors. As seen in Figure 2, when a remote isolated shunt sensor is
connected via the 71M6xx3, the samples associated with this current channel are not routed to the
multiplexer, and are instead transferred digitally to the 71M6543 via the isolation interface and are directly
stored in CE RAM. The MUX_SELn[3:0] I/O RAM control fields allow the MPU to configure the AFE for the
desired multiplexer sampling sequence. Refer to Table 1 and Table 2 for the appropriate CE code and the
corresponding AFE settings.
See Figure 31 for the meter wiring configuration corresponding to Figure 2.
VREF
IN*
IADC0
MUX
∆Σ ADC
CONVERTER
Local
Shunt
VREF
VREF
FIR
IADC1
VADC
VADC8 (VA)
22
VADC9 (VB)
VADC10 (VC)
IA
INP
INN
INP
SP
IADC2
IADC3
Remote
Shunt
71M6xx3
22
SN
CE RAM
IB
SP
SN
IADC4
IADC5
Remote
Shunt
Digital
Isolation
Interface
71M6xx3
71M6xx3
22
INN
INP
IC
SP
SN
IADC6
IADC7
Remote
Shunt
22
INN
71M6543
*IN = Neutral Current
9/17/2010
Figure 2: AFE Block Diagram (Shunts: One-Local, Three-Remotes)
12
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