ADE9078 datasheet(45/108 Pages) AD

45 / 108 page

ADE9078

Data Sheet

Rev. 0 | Page 44 of 107

To accumulate energy over a defined number of samples, use

the following settings:

•

Set the configuration register as follows:

•

EGY_LD_ACCUM = 1

•

EGY_TMR_MODE = 0

•

RD_RST_EN = 0

•

EGY_PWR_EN = 1

•

EGY_TIME to the desired number of samples

•

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.

Digital to Frequency Conversion—CFx Output

Many electricity meters are required to provide a pulse output

that is proportional to the energy being accumulated, with a

given pulse per kWh meter constant.

The ADE9078 includes four pulse outputs that are proportional

to the energy accumulation in the CF1 through CF4 output pins. A

block diagram of the CFx pulse generation is shown in Figure 65.

fDSP

RESERVED

xWATT

xVAR

xVA

xFVAR

RESERVED

xWATT

CFxSEL[2:0]

100

011

000

001

010

101

110

xWATT

111

TERMSELX[0]

PHASE A

TERMSELX[1]

PHASE B

TERMSELx[2]

CFxSEL[2:0]

WTHR

CFx_LT

CF_LTMR[18:0]

CFxDIS

4.096MHz

DIGITAL

FREQUENCY

512

CFxDEN

CF_ACC_CLR

CFx PIN

PULSE

WIDTH

CONFIG

ADE9078

CFx BITS

PHASE C

VARTHR

VATHR

WTHR

VARTHR

VATHR

WTHR

100

011

000

001

010

101

110

111

Figure 65. Digital to Frequency Conversion for CFx

Table 20. CFx Active Low Pulse Width and Duty Cycle Based on CFx_LT and CF_LTMR

CFx_LT

Active Low Pulse Width

for Low Frequencies (ms)

Active Low Pulse Width for

High Frequencies when

CFxDEN is Even

Active Low Pulse Width for

High Frequencies when

CFxDEN is Odd

Behavior when Entering No Load

50%

(1 + 1/CFxDEN) × 50%

If CFx is low, finish current pulse,

return high.

CF_LTMR × 6/CLKIN × 1000

50%

(1 + 1/CFxDEN) × 50%

If CFx is low, keep CFx low until the

no load state is finished.

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