Cirrus Logic CS5461A - Manual (Page 39)

CS5461A
DS661F3 39
9. BASIC APPLICATION CIRCUITS
Figure 15 shows the CS5461A configured to measure
power in a single-phase, 2-wire system while operating
in a single-supply configuration. In this diagram, a shunt
resistor is used to sense the line current and a voltage
divider is used to sense the line voltage. In this type of
shunt resistor configuration, the common-mode level of
the CS5461A must be referenced to the line side of the
power line. This means that the common-mode poten-
tial of the CS5461A will track the high-voltage levels, as
well as low-voltage levels, with respect to earth ground
potential. Isolation circuitry is required when an earth-
ground-referenced communication interface is connect-
ed. Figure 16 shows the same single-phase, two-wire sys-
tem with complete isolation from the power lines. This
isolation is achieved using three transformers: a general
purpose transformer to supply the on-board DC power;
a high-precision, low-impedance voltage transformer
with very little roll-off/phase-delay, to measure voltage;
and a current transformer to sense the line current.
Figure 17 shows a single-phase, 3-wire system. In
many 3-wire residential power systems within the Unit-
ed States, only the two line terminals are available (neu-
tral is not available).
Figure 18 shows the CS5461A
configured to meter a three-wire system with no neutral
available.
VA+ VD+
CS5461A
0.1 µF 470 µF
500 
470 nF
500
N
R 1 R 2
10 
14
VIN+
9
VIN-
IIN-
10
15
16
IIN+
PFMON
CPUCLK
XOUT
XIN
Optional
Clock
Source
Serial
Data
Interface
RESET
17
2
1
24
19
CS
7
SDI
23
SDO
6
SCLK
5
INT
20
E1
0.1 µF
VREFIN
12
VREFOUT
11
AGND DGND
13 4
3
4.096 MHz
0.1 µF
10 k 5 k
L
R
Shunt
R
V-
R
I-
R
I+
ISOLATIO
N
120 VAC
Mech. Counter
Stepper Motor
or
22
21
C
I-
C
I+
C
Idiff
C V-
C
V+
C
Vdiff
E2
Note:
Indicates common (floating) return.
Figure 15. Typical Connection Diagram (Single-phase, 2-wire – Direct Connect to Power Line)