71M6543HT datasheet(40/75 Pages) MAXIM

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71M6543FT/71M6543HT/

71M6543GT/71M6543GHT

Energy Meter ICs

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Functional Description

Theory of Operation

The energy delivered by a power source into a load can

be expressed as:

V(t)I(t)dt

= ∫

Assuming phase angles are constant, the following for-

mulae apply:

• P=RealEnergy[Wh]=VxAxcos(φ)xt

• Q=ReactiveEnergy[VARh]=VxAxsin(φ)xt

• S = Apparent Energy [VAh] =

For a practical meter, not only voltage and current ampli-

tudes, but also phase angles and harmonic content may

change constantly. Thus, simple RMS measurements are

inherently inaccurate. The 71M654xT, however, functions

by emulating the integral operation above by processing

current and voltage samples at a constant rate. As long

as the ADC resolution is high enough and the sample fre-

quencyisbeyondtheharmonicrangeofinterest,thecur-

rent and voltage samples, multiplied by the sample period

yield an accurate value for the instantaneous energy.

Summingtheinstantaneousenergyquantitiesovertime

provides accurate results for accumulated energy.

The application of 240V AC and 100A results in an accu-

mulation of 480Ws (= 0.133 Wh) over the 20ms period, as

indicated by the accumulated power curve. The described

sampling method works reliably, even in the presence of

dynamic phase shift and harmonic distortion.

Battery Modes

The 71M654xT can operate in one of four power modes:

mission (MSN), brownout (BRN), sleep (SLP), or LCD-

only (LCD) mode.

Shortly after system power (VV3P3SYS) is applied, the

part is in mission mode. MSN mode means that the part

is operating with system power and that the internal PLL

is stable. This mode is the normal operating mode where

the part is capable of measuring energy.

When system power is not available, the 71M654xT is in

one of three battery modes: BRN, SLP or LCD.

An internal comparator monitors the voltage at the

VV3P3A pin (note that VV3P3SYS and VV3P3A are typically

connected together at the PCB level). When the VV3P3A

dc voltage drops below 2.8 VDC, the comparator resets

an internal power status bit called V3OK. As soon as

system power is removed and V3OK = 0, the 71M654xT

switches to battery power (VBAT pin), notifies the MPU

by issuing an interrupt and updates the VSTAT[2:0]

system transitions from MSN to BRN mode. Depending

on the MPU code, the MPU can choose to stay in BRN

mode, or transition to LCD or to SLP mode. BRN mode is

similar to MSN mode except that resources powered by

VV3P3A power, such as the ADC are inaccurate. In BRN

mode the CE continues to run and should be turned off to

conserve VBAT power. Also, the PLL continues to function

atthesamefrequencyasinMSNmodeanditsfrequency

should be reduced to save power.

TMUX[5:0]

SIGNAL NAME

DESCRIPTION

RTCLK

32.768 kHz clock waveform

INT0 – DIG I/O

Interrupts

INT1 – DIG I/O

INT2 – CE_PULSE

INT3 – CE_BUSY

INT4 - VSTAT

INT5 – EEPROM/SPI

INT6 – XFER, RTC

RTM_CK(flash)

Note: All

TMUX2[4:0] values which are not shown are reserved.

Table 11. Test Ports (continued)

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