ADE7755ARSZ datasheet(19/20 Pages) AD

19 / 20 page

ADE7755

Rev. A | Page 19 of 20

NO LOAD THRESHOLD

The ADE7755 also includes a no load threshold and start-up

current feature that eliminates any creep effects in the meter. The

ADE7755 is designed to issue a minimum output frequency in all

modes except when SCF = 0 and S1 = S0 = 1. The no load detection

threshold is disabled in this output mode to accommodate

specialized application of the ADE7755. Any load generating a

frequency lower than this minimum frequency will not cause a

pulse to be issued on F1, F2, or CF. The minimum output

frequency is given as 0.0014% of the full-scale output frequency

for each of the fi frequencies (i = 1, 2, 3, or 4), see Table 6.

For example, in an energy meter with a meter constant of

100 imp/kWh on F1 and F2 using f2 (3.4 Hz), the maximum

output frequency at F1 or F2 is 0.0014% of 3.4 Hz or 4.76 × 10−5 Hz.

This is 3.05 × 10−3 Hz at CF (64 × F1 Hz). In this example, the no

load threshold is equivalent to 1.7 W of the load or a start-up

current of 8 mA at 220 V. IEC 1036 states that the meter must

start up with a load current equal to or less than 0.4% Ib. For a

5 A (Ib) meter, 0.4% Ib is equivalent to 20 mA. The start-up

current of this design therefore satisfies the IEC requirement.

As illustrated in this example, the choice of fi frequency

(i = 1, 2, 3, or 4) and the ratio of the stepper motor display

determine the start-up current.

ADE7755ARSZ 数据表(PDF) 19 Page - Analog Devices