ADE7761AARS-REF datasheet(22/24 Pages) AD

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ADE7761A

Rev. 0 | Page 22 of 24

Looking at Table 10, the closest frequency to 0.266 Hz

in Column 4 is 0.17 Hz. Therefore, F2 (3.4 Hz; see Table 6) is

selected for this design.

Frequency Outputs

Figure 2 is a timing diagram for the various frequency outputs.

The high frequency CF output is intended for communication

and calibration purposes. CF produces a 90 ms wide, active

high pulse (t4) at a frequency that is proportional to active

power. The CF output frequencies are given in Table 8. As with

F1 and F2, if the period of CF (t5) falls below 180 ms, the CF

pulse width is set to half the period. For example, if the CF

frequency is 20 Hz, the CF pulse width is 25 ms.

No-Load Threshold

The ADE7761A includes a no-load threshold and start-up

current feature that eliminates creep effects in the meter. The

ADE7761A is designed to issue a minimum output frequency.

Any load generating a frequency lower than this minimum

frequency does not cause a pulse to be issued on F1, F2, or CF.

The minimum output frequency is given as 0.0045% of the full-

scale output frequency. (See Table 8 for maximum output

frequencies for ac signals).

For example, an energy meter with a meter constant of

100 impulses per kWh on F1, F2 using SCF = 1, S1 = 0, and

S0 = 1, the maximum output frequency at F1 or F2 is 0.68 Hz

and 43.52 Hz on CF. The minimum output frequency at F1

or F2 is 0.0045% of 0.68 Hz or 3.06 × 10–5 Hz. This is 1.96 ×

10–3 Hz at CF (64 × F1 Hz).

In this example, the no-load threshold is equivalent to 1.1 W of

load or a startup current of 4.6 mA at 240 V. Compare this value

to the IEC 32053-21 specification, which states that the meter

must start up with a load equal to or less than 0.4% of IB. For a

5 A (I

) meter, 0.4% of IB is equivalent to 20 mA.

Note that the no-load threshold is not enabled when using the

high CF frequency mode: SCF = 0, S1 = S0 = 1.

NEGATIVE POWER INFORMATION

The ADE7761A detects when the current and voltage channels

have a phase shift greater than 90°. This mechanism can detect

a wrong connection of the meter or the generation of negative

power. The REVP pin output goes active high when negative

power is detected and active low when positive power is

detected. The REVP pin output changes state as a pulse is

issued on CF.

ADE7761AARS-REF 数据表(PDF) 22 Page - Analog Devices

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