71M6543HT-IGTRSLASHF datasheet(46/75 Pages) MAXIM

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71M6543FT/71M6543HT/

71M6543GT/71M6543GHT

Energy Meter ICs

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Applications Information

Connecting 5V Devices

All digital input pins of the 71M654xT are compatible with

external 5V devices. I/O pins configured as inputs do not

requirecurrent-limitingresistorswhentheyareconnected

to external 5V devices.

Direct Connection of Sensors

The 71M654xT supports direct connection of current

transformer and shunt-fed sensors.

Using the 71M6543FT/HT/GT/GHT

with Local Sensors

The 71M6543FT/HT/GT/GHT can be configured to oper-

ate with locally connected current sensors. All current

inputs are connected to a current transformer (CT) and are

therefore isolated. This configuration implements a poly-

phase measurement with tamper-detection using one

current sensor to measure the neutral current. For best

performance, all current sensor inputs are configured for

differential mode.

Using the 71M6543FT/HT/GT/GHT

with Remote Sensors

The 71M6543FT/HT/GT/GHT can be configured to oper-

ate with 71M6x03 remote sensor interfaces and current

shunts. This configuration implements a polyphase mea-

surement with tamper-detection. For best performance,

the IADC0-IADC1 current sensor input is configured

for differential mode (DIFFA_E = 1). The outputs of the

71M6x03 isolated sensor interface are routed through

a pulse transformer, which is connected to the current

input pins (IADC2-IADC7). The current input pins (IADC2-

IADC7) must be configured for remote sensor communi-

cation (i.e., RMT_E =1).

Metrology Temperature Compensation

Since the VREF bandgap amplifier is chopper-stabilized

the DC offset voltage (the most significant long-term

drift mechanism in bandgap voltage references) is

automatically removed by the chopper circuit. Both the

71M654xT and the 71M6x03 feature chopper circuits

for their respective VREF voltage reference. VREF is

trimmed to a target value of 1.195V during the device

manufacturing process and the result of the trim stored in

nonvolatile fuses.

For the 71M654xT device (Q0.5% energy accuracy),

the TRIMT[7:0] value can be read by the MPU during

initialization in order to calculate parabolic temperature

compensation coefficients suitable for each individual

71M654xT device. The resulting temperature coefficient

for VREF in the 71M654xT is ±40 ppm/°C.

By using the trim information in the TRIMT register and

the sensed temperature, a gain adjustment for the sensor

can be computed. See the 71M6543FT/HT/GT/GHT

User’s Guide for more information about compensating

sensors for temperature variations.

Connecting I2C EEPROMs

I2C EEPROMs or other I2C compatible devices should

be connected to the DIO pins SEGDIO2 and SEGDIO3.

Pullup resistors of roughly 10kΩ to VV3P3D (to ensure

operation in BRN mode) should be used for both SDCK

and SDATA signals. The DIO_EEX[1:0] field in I/O

RAM must be set to 01 in order to convert the DIO pins

SEGDIO2 and SEGDIO3 to I2C pins SDCK and SDATA.

Connecting Three-Wire EEPROMs

MICROWIRE EEPROMs and other compatible devices

should be connected to the DIO pins SEGDIO2/SDCK

and SEGDIO3/SDATA.

UART0

The UART0 RX pin should be pulled down by a 10kΩ

resistor and additionally protected by a 100pF ceramic

capacitor.

Optical Interface

The OPT_TX and OPT_RX pins can be used for a regular

serial interface (by connecting a RS_232 transceiver for

example), or they can be used to directly operate optical

components (for example, an infrared diode and pho-

totransistor implementing a FLAG interface). Figure 16

shows the basic connections for UART1. The OPT_TX

pin becomes active when the I/O RAM control field OPT_

TXE (I/O RAM 0x2456[3:2]) is set to 00.

The polarity of the OPT_TX and OPT_RX pins can be

inverted with the configuration bits, OPT_TXINV and

OPT_RXINV, respectively.

The OPT_TX output may be modulated at 38kHz when

system power is present. Modulation is not available in

BRN mode. The OPT_TXMOD bit enables modulation.

The duty cycle is controlled by OPT_FDC[1:0], which can

select 50%, 25%, 12.5%, and 6.25% duty cycle. A 6.25%

duty cycle means OPT_TX is low for 6.25% of the period.

The OPT_RX pin uses digital signal thresholds. It may

need an analog filter when receiving modulated optical

signals.

With modulation, an optical emitter can be operated at

higher current than nominal, enabling it to increase the

distance along the optical path.

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