CS5461 datasheet(41/46 Pages) CIRRUS

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CS5461

DS546PP2

8. BASIC APPLICATION CIRCUITS

Figure 14 shows the CS5461 connected to a service

to measure power in a single-phase 2-wire system

while operating in a single supply configuration.

Note that in this diagram the shunt resistor used to

monitor the line current is connected on the “Line”

(hot) side of the power mains. In most residential

power metering applications, the power meter’s

current-sense shunt resistor is intentionally placed

on the hot side of the power mains in order to detect

a subscriber’s attempt to steal power. In this type of

shunt-resistor configuration, the common-mode

level of the CS5461 must be referenced to the hot

side of the power line; which means the com-

mon-mode potential of the CS5461 will typically

oscillate to very high voltage levels with respect to

earth ground potential. If digital communication

networks require that the CMOS-level digital inter-

face be referenced to an earth ground, the serial in-

terface pins on the CS5461 must be isolated from

the external digital interface.

Figure 15 shows the same single-phase two-wire

system with complete isolation from the power

lines. This isolation is achieved using three trans-

formers: a general purpose transformer to supply

the on-board DC power; a high-precision, low im-

pedance voltage transformer, with very little

roll-off/phase-delay, to measure voltage; and a cur-

rent transformer to sense the line current. Because

the CS5461 is not directly connected to the power

mains, no isolation is necessary on the CS5461’s

digital interface.

Figure 16 shows a single-phase 3-wire system. In

many 3-wire residential power systems within the

United States, only the two line terminals are avail-

able (neutral is not available). Figure 17 shows the

CS5461 configured to meter a three-wire system

with no neutral available.

VA+

VD+

CS5461

0.1 µF

100 µF

500 Ω

470 nF

500

10 Ω

VIN+

VIN-

IIN-

IIN+

PFMON

CPUCLK

XOUT

XIN

Optional

Clock

Source

Serial

Data

Interface

RESET

SDI

SDO

SCLK

INT

EDIR

EOUT

0.1 µF

VREFIN

VREFOUT

VA-

DGND

To Service

2.5 MHz to

20 MHz

0.1 µF

10 kΩ

5kΩ

Shunt

V+

V-

I-

I+

120 VAC

Mech. Counter

Stepper Motor

Figure 14. Typical Connection Diagram (One-Phase 2-Wire, Direct Connect to Power

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