71M6545HT-IGTSLASHF datasheet(21/66 Pages) MAXIM

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71M6545T/71M6545HT

Energy Meter ICs

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Pins IADC0-IADC1 can be programmed individually to be

differential or single-ended. For most applications IADC0-

IADC1 are configured as a differential input to work with

a shunt or CT directly interfaced to the IADC0-IADC1

differential input with the appropriate external signal con-

ditioning components.

The performance of the IADC0-IADC1 pins can be

enhanced by enabling a preamplifier with a fixed gain of 8.

When the PRE_E bit = 1, IADC0-IADC1 become the inputs

to the 8x preamplifier, and the output of this amplifier is

supplied to the multiplexer. The 8x amplification is useful

when current sensors with low sensitivity, such as shunt

resistors, are used. With PRE_E set, the IADC0-IADC1

input signal amplitude is restricted to 31.25 mV peak.

When shunt resistors are used as current sense ele-

ments on all current inputs, the IADC0-IADC1 pins are

configured for differential mode to interface to a local

shunt by setting the DIFFA_E control bit. Meanwhile, the

IADC2-IADC7 pins are re-configured as digital balanced

pair to communicate with a 71M6x03 isolated sensor

interface by setting the RMT_E control bit. The 71M6x03

communicates with the 71M654xT using a bidirectional

digital data stream through an isolating low-cost pulse

transformer. The 71M654xT also supplies power to the

71M6x03 through the isolating transformer.

When using current transformers the IADC2-IADC7 pins

are configured as local analog inputs (RMT_E = 0). The

IADC0-IADC1 pins cannot be configured as a remote

sensor interface.

Input Multiplexer

When operating with local sensors, the input multiplexer

sequentially applies the input signals from the analog

input pins to the input of the ADC. One complete sam-

pling sequence is called a multiplexer frame. The multi-

plexer of the 71M6545T/HT can select up to seven input

signals (three voltage inputs and four current inputs) per

multiplexer frame. The multiplexer always starts at state

1 and proceeds until as many states as determined by

MUX_DIV[3:0] have been converted.

The 71M6545T/HT requires CE code that is written for

the specific application. Moreover, each CE code requires

specific AFE and MUX settings in order to function properly.

Contact Maxim Integrated for specific information about alter-

native CE codes.

For a polyphase configuration with neutral current sens-

ing using shunt resistor current sensors and the 71M6xx3

isolated sensors, as shown in Figure 3, the IADC0-IADC1

input must be configured as a differential input, to be con-

nected to a local shunt. The local shunt connected to the

IADC0-IADC1 input is used to sense the Neutral current.

The voltage sensors (VADC8-VADC10) are also directly

connected to the 71M6545T/HT and are also routed

though the multiplexer. Meanwhile, the IADC2-IADC7

current inputs are configured as remote sensor digital

interfaces and the corresponding samples are not routed

through the multiplexer.

For a polyphase configuration with optional neutral current

sensing using Current Transformer (CTs) sensors, all four

current sensor inputs must be configured as differential

inputs. IADC2-IADC3 is connected to phase A, IADC4-

IADC5 is connected to phase B, and IADC6-IADC7

is connected to phase C. The IADC0-IADC1 current

sensor input is optionally used to sense the Neutral

current for anti-tampering purposes. The voltage sensors

(VADC8-VADC10), typically resistive dividers, are directly

connected to the 71M6545T/HT. No 71M6xx3 isolated

sensors are used in this configuration and all signals are

routed though the multiplexer.

The multiplexer sequence shown in Figure 4 corresponds

to the configuration shown in Figure 3. The frame duration

is 13 CK32 cycles (where CK32 = 32,768Hz), therefore,

the resulting sample rate is 32,768Hz/13 = 2,520.6Hz.

Note that Figure 4 only shows the currents that pass

through the 71M6545T/HT multiplexer, and does not show

the currents that are copied directly into CE RAM from the

remote sensors (see Figure 3), which are sampled during

the second half of the multiplexer frame. The two unused

conversion slots shown are necessary to produce the

desired 2,520.6Hz sample rate.

The multiplexer sequence shown in Figure 5 corresponds

to the CT configuration shown in Figure 2. Since in

this case all current sensors are locally connected to

the 71M6545T/HT, all currents are routed through the

multiplexer, as seen in Figure 2. For this multiplexer

sequence, the frame duration is 15 CK32 cycles (where

CK32 = 32,768Hz), therefore, the resulting sample rate is

32,768Hz/15 = 2,184.5Hz.

71M6545HT-IGT/F Datasheet(PDF) 21 Page - Maxim Integrated Products

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