71m6545h-igtr/f Maxim Integrated Products, Inc., 71m6545h-igtr/f Datasheet - Page 13

• Manufacturer Part Number: 71m6545h-igtr/f
• Description: Metrology Processors
• Manufacturer: Maxim Integrated Products, Inc.

PDS_6545_009
The 71M6545/H AFE can also be directly interfaced to Current Transformers (CTs), as seen in
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
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
26
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
for detailed connections for each type of sensor.
Figure 28
for the meter wiring configuration corresponding to
CT
CT
CT
CT
IN*
IC
IA
IB
© 2008–2011 Teridian Semiconductor Corporation
VADC10 (VC)
VADC9 (VB)
VADC8 (VA)
Figure 3. AFE Block Diagram (Four CTs)
IADC6
IADC7
IADC0
IADC1
IADC4
IADC5
IADC2
IADC3
*IN = Neutral Current
MUX
VREF
VADC
71M6545/H
VREF
VREF
CONVERTER
Figure
∆Σ ADC
FIR
Figure
23,
22
Figure
CE RAM
3.
10/7/2010
24,
Data Sheet 71M6545/H
Figure 25
and
Figure
Figure
3.
13