ADE7758_15 datasheet(51/72 Pages) AD

51 / 72 page

Data Sheet

ADE7758

Rev. E | Page 51 of 72

To set APCFNUM (0x45) and APCFDEN (0x46) to the

calculated value to perform a coarse adjustment on the

imp/kW-hr ratio, use Equation 45 to Equation 47.

kHz

5415

130

500

220

APCF

NOMINAL

()

1.956

cos

3600

1000

220

3200

EXPECTED

APCF

277

956

541

INT

⎟

⎠

⎞

⎜

⎝

⎛

APCFDEN

Under the test conditions above, the AWATTHR register value

is 15559d after the LENERGY interrupt. Using Equation 60 and

Equation 61, the value to be written to AWG is −199d, 0xF39.

[]

Selected

Phases

No.

FREQ

LINECYC

AccumTime

−6

]

[

6.832128s

2085

800

−

AccumTime

14804

277

3600

1000

832

220

3200

EXPECTED

WATTHR

0xF39

–199

–198.87640

15559

14804

⎟

⎠

⎞

⎜

⎝

⎛

−

xWG

Using Equation 66, the Wh/LSB constant is

0.000282

14804

3600

832

220

LSB

Phase Calibration Using Line Accumulation

The ADE7758 includes a phase calibration register on each

phase to compensate for small phase errors. Large phase errors

should be compensated by adjusting the antialiasing filters. The

ADE7758 phase calibration is a time delay with different weights

in the positive and negative direction (see the Phase

Compensation section). Because a current transformer is a

source of phase error, a fixed nominal value can be decided on to

load into the xPHCAL (0x3F to 0x41) registers at power-up.

During calibration, this value can be adjusted for CT-to-CT

error. Figure 83 shows the steps involved in calibrating the

phase using the line accumulation mode.

STEP 1

SET LCYCMODE,

LINECYC AND MASK

REGISTERS

STEP 2

SET UP SYSTEM FOR

ITEST,VNOM,PF = 0.5,

INDUCTIVE

STEP 3

RESET STATUS

STEP 4

READ ALL xWATTHR

REGISTERS AFTER

LENERGY

INTERRUPT

STEP 5

CALCULATE PHASE

ERROR IN DEGREES

FOR ALL PHASES

STEP 6

CALCULATE AND

WRITE TO ALL

xPHCAL REGISTERS

Figure 83. Phase Calibration Using Line Accumulation

Step 1: If the values were changed after gain calibration, Step 1,

Step 3, and Step 4 from the gain calibration should be repeated

to configure the LCYCMODE and LINECYC registers.

Step 2: Set the test system for ITEST, VNOM, and 0.5 power factor

inductive.

Step 3: Reset the interrupt status register by reading RSTATUS

(0x1A).

Step 4: The xWATTHR registers should be read after the

LENERGY interrupt. Measure the percent error in the energy

compared to the energy register readings at unity power factor

(after gain calibration) using Equation 69. The readings at unity

power factor should have been repeated after the gain calibration

and stored for use in the phase calibration routine.

–

xWATTHR

Error

(69)

Step 5: Calculate the Phase Error in degrees using the equation

()

⎟

⎠

⎞

⎜

⎝

⎛

–

Error

Arcsin

Error

Phase

(70)

Step 6: Calculate xPHCAL and write to the xPHCAL registers

(0x3F to 0x41).

360

)

(

Period

Line

Weight

LSB

PHCAL

Error

Phase

xPHCAL

(71)

where PHCAL_LSB_Weight is 1.2 μs if the %Error is negative

or 2.4 μs if the %Error is positive (see the Phase Compensation

section).

ADE7758 Datasheet(PDF) 51 Page - Analog Devices

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