ADE9078ACPZ datasheet(44/108 Pages) AD

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Data Sheet

ADE9078

Rev. 0 | Page 43 of 107

For example, with MTEN = 0, for single-point gain compensation

and AIGAIN, AVGAIN, APGAIN, and AWATTOS all = 0, the

Phase A total active energy has a digital gain of 1. Then, the

Phase A total active energy, accumulated in the user accessible

accumulator, overflows in 211 sec with the nominal full-scale

AWATT value of 20,823,646.

Maximum User Energy Accumulator Time (sec) =

sec

211

4000

20,823,646

















Accessing the User Energy Registers

Each 45-bit user accessible signed energy accumulator is

divided into two registers: a register containing the 32 MSBs,

xHR_HI, and a register containing the 13 LSBs, xHR_LO, as

shown in Figure 64.

fDSP

INTERNAL ENERGY ACCUMULATOR

031

AWATTHR_HI

AWATT

AWATTHR_LO

Figure 64. Internal Energy Register to AWATTHR_HI and AWATTHR_LO

The expected user energy accumulation can be calculated

according to the following formula based on the average

AWATT value:

User Energy Accumulation = AWATT × (EGY_TIME + 1)

Then, AWATTHR_HI contains 32 MSBs, which can be

calculated by rounding the following equation down to the

nearest whole number:

AWATTHR_HI = ROUNDDOWN(User Energy

Accumulation × 2−13)

where ROUNDDOWN() is a function to round down to the

nearest integer.

Finally, AWATTHR_LO is calculated based on the two previous

values, as follows:

AWATTHR_LO = (User Energy Accumulation −

AWATT_EGY_USER_HI × 213) × 219

For example, if 4000 samples of AWATT are accumulated, with

full-scale inputs, the expected value of AWATTHR_HI is

0x009B 25F4 and AWATTHR_LO is 0xE600 0000.

User Energy Accumulation = 20,823,646 × (3999 + 1) =

83,294,584,000

AWATTHR_HI = ROUNDDOWN(83,294,584,000 × 2−13) =

10,167,795 = 0x009B 25F3

AWATTHR_LO = (83,294,584,000 − 10,167,795 × 213) × 219 =

3,858,759,680 = 0xE600 0000

To determine the consumption in watthours, the meter is

calibrated using the xIGAIN, xVGAIN, and xPGAIN registers.

Then, xWATTHR_HI × watthour/LSB = watthour. The

watthour/LSB constant is the same for all meters.

Read User Energy Register with Reset

If the RD_RST_EN bit is set in the EP_CFG register, when a

user accessible energy register is read, its contents are reset.

For example, if AWATTHR_HI is read, the AWATTHR_HI register

value goes to zero. The AWATTHR_LO register contents are not

modified.

It is not recommended to read the xHR_LO registers with reset.

User Energy Register Use Models

There are three main use models for energy accumulation, as

follows:



Read the energy register with reset



Accumulate energy over a defined number of line cycles



Accumulate energy over a defined number of samples

To read the energy register with reset, use the following settings:



Set the configuration register as follows:



EGY_LD_ACCUM = 0



EGY_TMR_MODE = 0



RD_RST_EN = 1



EGY_PWR_EN = 1



EGY_TIME = 1



For the output, read only the xHR_HI register, which has

enough resolution for most applications. The xHR_LO

to be read by the user.



Set the maximum time before reading xHR_HI to prevent

overflow with full-scale inputs to 211 sec.

To accumulate energy over a defined number of line cycles, use

the following settings:



Set the configuration register as follows:



EGY_LD_ACCUM = 1



EGY_TMR_MODE = 1



RD_RST_EN = 0



EGY_PWR_EN = 1



EGY_TIME to the desired number of half line cycles



For the output, the xHR_HI register has enough resolution for

most applications. To maintain perfect synchronization

with the CF pulse output, the xHR_LO must be read as

well because it is cleared at every EGYRDY cycle.



Set the maximum time before reading xHR_HI to prevent

overflow with full-scale inputs to 26.4 sec.

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