71M6545 Datasheet, PDF (12/134 Pages) Maxim Integrated Products – Four-Quadrant Metering, Phase Metrology Processors Flash/RAM Size

Data Sheet 71M6545/H
PDS_6545_009
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. 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 or by the host processor over the
SPI interface. The 71M6545/H AFE may also be augmented by isolated 71M6xx3 sensors in order to
support low-cost current shunt sensors. Figure 2 and Figure 3 show two of the most common
configurations; other configurations are possible. Sensors that are connected directly to the 71M6545/H
(i.e., IADC0-IADC1, VADC8, VADC9 and VADC10) are multiplexed into the single second-order sigma-
delta ADC input for sampling in the 71M6545/H. The 71M6545/H 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 71M6545/H 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 71M6545/H 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 27 for the meter wiring configuration corresponding to Figure 2.
IN*
Local
Shunt
IA
Remote
Shunt
INP
SP
71M6xx3
SN
INN
IB
Remote
Shunt
INP
SP
71M6xx3
SN
INN
IADC0
IADC1
VADC8 (VA)
VADC9 (VB)
VADC10 (VC)
IADC2
IADC3
IADC4
IADC5
MUX
VREF
VREF
VADC
∆Σ ADC
CONVERTER
VREF
FIR
22
Digital
Isolation
Interface
22
CE RAM
22
IC
INP
SP
IADC6
Remote
Shunt
71M6xx3
SN
IADC7
22
INN
*IN = Neutral Current
71M6545/H
10/7/2010
Figure 2: AFE Block Diagram (Shunts: One-Local, Three-Remotes)
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