71M6541D Datasheet, PDF (14/166 Pages) Maxim Integrated Products – 0.1% Accuracy Over 2000:1 Current Range Energy Meter ICs

71M6541D/F/G and 71M6542F/G Data Sheet
Figure 5 shows the 71M6542F/G multiplexer interface with one local and one remote resistive shunt
sensor. As seen in Figure 5, when a remote isolated shunt sensor is connected via the 71M6x01, the
samples associated with this current channel are not routed to the multiplexer, and are instead
transferred digitally to the 71M6542F/G via the digital isolation interface and are directly stored in CE
RAM.
See Figure 6 for the multiplexer timing sequence corresponding to Figure 5. See Figure 38 for the meter
configurations corresponding to Figure 5.
IA
IAP
Local
Shunt
IAN
VADC10 (VA)
MUX
VREF
VREF
VADC
∆Σ ADC
CONVERTER
VREF
FIR
22
VADC9 (VB)
IB
INP
SP
IBP
Remote
Shunt
71M6x01
SN
IBN
INN
Digital
Isolation
Interface
CE RAM
22
71M6542F
11/5/2010
Figure 5. 71M6542F/G AFE Block Diagram with 71M6x01
2.2.1 Signal Input Pins
The 71M6541D/F/G features five ADC inputs. The 71M6542F/G features six ADC inputs.
IAP-IAN and IBP-IBN are intended for use as current sensor inputs. These four current sensor inputs can be
configured as four single-ended inputs, or can be paired to form two differential inputs. For best
performance, it is recommended to configure the current sensor inputs as differential inputs (i.e., IAP-IAN
and IBP-IBN). The first differential input (IAP-IAN) features a pre-amplifier with a selectable gain of 1 or 8,
and is intended for direct connection to a shunt resistor sensor, and can also be used with a Current
Transformer (CT). The remaining differential pair (i.e., IBP-IBN) may be used with CTs, or may be enabled
to interface to a remote 71M6x01 isolated current sensor providing isolation for a shunt resistor sensor using
a low cost pulse transformer.
The remaining input in the 71M6541D/F/G (VA) is single-ended, and is intended for sensing the line voltage
in a single-phase meter application using Equation 0 or 1 (see 2.3.4 Meter Equations on page 25). The
71M6542F/G features an additional single-ended voltage sensing input (VB) to support bi-phase
applications using Equation 2. These single-ended inputs are referenced to the V3P3A pin.
All analog signal input pins measure voltage. In the case of shunt current sensors, currents are sensed as a
voltage drop in the shunt resistor sensor. Referring to Figure 3, shunt sensors can be connected directly to
the 71M654x (referred to as a ‘local’ shunt sensor) or connected via an isolated 71M6x01 (referred to as a
‘remote’ shunt sensor). In the case of Current Transformers (CT), the current is measured as a voltage
across a burden resistor that is connected to the secondary winding of the CT. Meanwhile, line voltages are
sensed through resistive voltage dividers. The VA and VB pins (VB is available in the 71M6542F/G only)
are single-ended and their common return is the V3P3A pin.
Pins IAP-IAN can be programmed individually to be differential or single-ended as determined by the
DIFFA_E (I/O RAM 0x210C[4]) control bit. However, for most applications, IAP-IAN are configured as a
differential input to work with a shunt or CT directly interfaced to the IAP-IAN differential input with the
appropriate external signal conditioning components (see 4.2 Direct Connection of Sensors on page 92).