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ADE7751

Energy Metering IC with On-Chip Fault Detection

Analog Devices 

PRELIMINARY TECHNICAL DATA

ADE7751

When selecting a suitable F1–4 frequency for a meter design, the

frequency output at IMAX (maximum load) with a meter constant

of 100 imp/kWhr should be compared with Column 4 of Table VI.

The frequency that is closest in Table VI will determine the best

choice of frequency (F1–4). For example, if a meter with a maxi-

mum current of 25 A is being designed, the output frequency on F1

and F2, with a meter constant of 100 imp/kWhr, is 0.153 Hz at 25 A

and 220 V (from Table V). Looking at Table VI, the closest

frequency to 0.153 Hz in column four is 0.17 Hz. Therefore F2

(3.4 Hz—see Table II) is selected for this design.

Frequency Outputs

Figure 1 shows a timing diagram for the various frequency

outputs. The outputs F1 and F2 are the low-frequency outputs

that can be used to directly drive a stepper motor or electrome-

chanical impulse counter. The F1 and F2 outputs provide two

alternating low-going pulses. The pulsewidth (t1) is set at 275 ms

and the time between the falling edges of F1 and F2 (t3) is

approximately half the period of F1 (t2).

If, however, the period of F1 and F2 falls below 550 ms (1.81 Hz),

the pulsewidth of F1 and F2 is set to half of their period. The maxi-

mum output frequencies for F1 and F2 are shown in Table III.

The high-frequency CF output is intended to be used for

communications and calibration purposes. CF produces a

90 ms wide active high pulse (t4) at a frequency that is propor-

tional to active power. The CF output frequencies are given in

Table IV. As in the case of F1 and F2, if the period of CF (t5)

falls below 180 ms, the CF pulsewidth 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 ADE7751 also includes a “no load threshold” and “start-

up current” feature that will eliminate any creep effects in the

meter. The ADE7751 is designed to issue a minimum output

frequency. 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 F1–4 frequency

selections (see Table II). For example, for an energy meter with

a meter constant of 100 imp/kWhr on F1, F2 using F2 (3.4 Hz),

the maximum output frequency at F1 or F2 would be 0.0014%

of 3.4 Hz or 4.76 × 10–5 Hz. This would be 3.05 × 10–3 Hz at

CF (64 × F1 Hz). In this example, the no load threshold would be

equivalent to 1.7 W of load or a start-up current of 8 mA at 220 V.

Compare this value to the IEC1036 specification, which states

that the meter must start up with a load equal to or less than

0.4% Ib. For a 5 A(Ib) meter, 0.4% of Ib is equivalent to 20 mA.

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

24-Lead Plastic DIP

(N-24)

1.275 (32.30)

1.125 (28.60)

24

1

PIN 1

0.210

(5.33)

MAX

0.200 (5.05)

0.125 (3.18)

0.022 (0.558)

0.014 (0.356)

0.100

(2.54)

BSC

13 0.280 (7.11)

12 0.240 (6.10)

0.325 (8.25)

0.300 (7.62)

0.060 (1.52)

0.015 (0.38)

0.195 (4.95)

0.150

(3.81)

MIN

0.070 (1.77) SEATING

0.045 (1.15) PLANE

0.115 (2.93)

0.015 (0.381)

0.008 (0.204)

24-Shrink Small Outline Package

(RS-24)

24

0.311 (7.9)

0.301 (7.64)

1

0.328 (8.33)

0.318 (8.08)

13

0.212 (5.38)

0.205 (5.207)

12

0.078 (1.98) PIN 1

0.068 (1.73)

0.07 (1.78)

0.066 (1.67)

0.008 (0.203)

0.0256

(0.65)

0.002 (0.050) BSC

8°

0.015 (0.38) SEATING 0.009 (0.229) 0°

0.010 (0.25) PLANE 0.005 (0.127)

0.037 (0.94)

0.022 (0.559)

–16–

REV. PrA

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