71M6545 Datasheet, PDF (13/134 Pages) Maxim Integrated Products – Four-Quadrant Metering, Phase Metrology Processors Flash/RAM Size

PDS_6545_009
Data Sheet 71M6545/H
The 71M6545/H AFE can also be directly interfaced to Current Transformers (CTs), as seen in Figure 3.
In this case, all voltage and current channels are multiplexed into a single second-order sigma-delta ADC
in the 71M6545/H and the 71M6xx3 remote isolated sensors are not used. The fourth CT and the
measurement of Neutral current via the IADC0-IADC1 current channel are optional.
See Figure 28 for the meter wiring configuration corresponding to Figure 3.
VREF
IA
IADC2
CT
IADC3
IB
IADC4
CT
IADC5
MUX
VREF
VADC
∆Σ ADC
CONVERTER
VREF
FIR
22
CE RAM
IC
IADC6
CT
IADC7
IN*
IADC0
CT
IADC1
VADC8 (VA)
VADC9 (VB)
VADC10 (VC)
*IN = Neutral Current
71M6545/H
10/7/2010
Figure 3. AFE Block Diagram (Four CTs)
2.2.1 Signal Input Pins
The 71M6545/H features eleven ADC input pins.
IADC0 through IADC7 are intended for use as current sensor inputs. These eight current sensor inputs can
be configured as eight single-ended inputs, or can be paired to form four differential inputs. For best
performance, it is recommended to configure the current sensor inputs as differential inputs (i.e., IADC0-
IADC1, IADC2-IADC3, IADC4-IADC5 and IADC6-IADC7). The first differential input (IADC0-IADC1)
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 three remaining differential
pairs (i.e., IADC2-IADC3, IADC4-IADC5 and IADC6-IADC7) may be used with CTs, or may be enabled to
interface to a remote 71M6xx3 isolated current sensor providing isolation for a shunt resistor sensor using a
low cost pulse transformer.
The remaining three inputs VADC8 (VA), VADC9 (VB) and VADC10 (VC) are single-ended, and are
intended for sensing each of the phase voltages in a poly-phase meter application. These three single-
ended inputs are referenced to the V3P3A pin.
All ADC input pins measure voltage. In the case of shunt current sensors, currents are sensed as a voltage
drop in the shunt resistor 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 of the CT. Meanwhile, line voltages are
sensed through resistive voltage dividers. The VADC8 (VA), VADC9 (VB) and VADC10 (VC) pins are
single-ended and their common return is the V3P3A pin. See Figure 23, Figure 24, Figure 25 and Figure
26 for detailed connections for each type of sensor.
Pins IADC0-IADC1 can be programmed individually to be differential or single-ended as determined by
the DIFF0_E (I/O RAM 0x210C[4]) control bit. However, for most applications, IADC0-IADC1 are
v1.0
© 2008–2011 Teridian Semiconductor Corporation
13