71M6545HT-IGTSLASHF datasheet(55/66 Pages) MAXIM

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71M6545T/71M6545HT

Energy Meter ICs

www.maximintegrated.com

CE Interface Description

CE Program

The CE performs the precision computations necessary to

accurately measure energy. These computations include

offset cancellation, phase compensation, product smooth-

ing, product summation, frequency detection, VAR calcula-

tion, sag detection and voltage phase measurement.

The CE program is supplied by Maxim Integrated as a

data image that can be merged with the MPU operational

code for meter applications. Typically, the CE program

provided with the demonstration code covers most appli-

cations and does not need to be modified. Other varia-

tions of CE code are available. Contact your local Maxim

Integrated representative to obtain the appropriate CE

code required for a specific application.

CE Data Format

All CE words are 4 bytes. Unless specified otherwise,

they are in 32-bit two’s complement format

(-1 = 0xFFFFFFFF). Calibration parameters are defined in

flash memory (or external EEPROM) and must be copied

to CE data memory by the MPU before enabling the CE.

Internal variables are used in internal CE calculations.

Input variables allow the MPU to control the behavior of

the CE code. Output variables are outputs of the CE cal-

culations. The corresponding MPU address for the most

significant byte is given by 0x0000 + 4 x CE_address and

by 0x0003 + 4 x CE_address for the least significant byte.

Constants

• Sampling Frequency: 2520.62Hz.

• F0: Frequency of the mains phases (typically 50Hz or

60Hz).

• IMAX: RMS current corresponding to 250mV peak

(176.8 mVRMS) at the inputs IA and IB. IMAX needs

to be adjusted if the preamplifier is activated for the

IAP-IAN inputs. For a 250μΩ shunt resistor, IMAX

becomes 707A (176.8 mVRMS/250FI = 707.2ARMS).

• VMAX: RMS voltage corresponding to 250mV peak at

the VA and VB inputs.

• NACC: Accumulation count for energy measurements

is SUM_SAMPS[12:0]. The duration of the accumu-

lation interval for energy measurements is SUM_

SAMPS[12:0]/FS.

• X: Gain constant of the pulse generators. Its value is

determined by PULSE_FAST and PULSE_SLOW.

• Voltage LSB (for sag threshold) = VMAX x 7.8798

x10-9 V.

The system constants IMAX and VMAX are used by the

MPU to convert internal digital quantities (as used by the

CE) to external, i.e., metering quantities. Their values are

determined by the scaling of the voltage and current sen-

sors used in an actual meter.

Environment

Before starting the CE using the CE_E bit (I/O RAM

0x2106[0]), the MPU has to establish the proper environ-

ment for the CE by implementing the following steps:

• Locate the CE code in flash memory using CE_LCTN[5:0].

• Load the CE data into RAM.

• Establish the equation to be applied in EQU[2:0].

• Establish the number of samples per accumulation

period in SUM_SAMPS[12:0].

• Establish the number of cycles per ADC multiplexer

frame (MUX_DIV[3:0]).

• Apply proper values to MUXn_SEL, as well as proper

selections for DIFFn_E and RMT_E in order to config-

ure the analog inputs.

• Initialize any MPU interrupts, such as CE_BUSY,

XFER_BUSY, or the power failure detection interrupt.

• VMAX = 600V, IMAX = 707A, and kH = 1Wh/pulse are

assumed as default settings

When different CE codes are used, a different set of envi-

ronment parameters need to be established. The exact

NAME

LOCATION RST WK DIR

DESCRIPTION

WAKE_ARM

28B2[5]

– R/W Arms the WAKE timer and loads it with WAKE_TMR[7:0]. When SLEEP or LCD_ONLY is asserted by the MPU, the

WAKE timer becomes active.

WF_PB

28B1[3]

–

R Indicates that the PB caused the part to wake.

WF_RX

28B1[4]

–

R Indicates that RX caused the part to wake.

WF_CSTART

WF_RST

WF_RSTBIT

WF_OVF

WF_ERST

WF_BADVDD

28B0[7]

28B0[6]

28B0[5]

28B0[4]

28B0[3]

28B0[2]

–

R Indicates that the Reset pin, Reset bit, ERST pin, Watchdog timer, the cold start detector, or bad VBAT caused the

part to reset.

71M6545HT-IGT/F Datasheet(PDF) 55 Page - Maxim Integrated Products

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