EVAL-ADE7755ZEB Datasheet, PDF (19/20 Pages) Analog Devices – Energy Metering IC with Pulse Output

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.
ADE7755
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.
Rev. A | Page 19 of 20