ADE7755ARSRL Ver la hoja de datos (PDF) - Analog Devices
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ADE7755ARSRL Datasheet PDF : 16 Pages
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ADE7755
PRELIMINARY TECHNICAL DATA
Table VI. F1 and F2 Frequency with Half-Scale AC Inputs
S1 S0 F1–4
0 0 1.7
0 1 3.4
1 0 6.8
1 1 13.6
Frequency on F1 and F2
CH1 and CH2 Half-Scale AC Inputs
0.085 Hz
0.17 Hz
0.34 Hz
0.68 Hz
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
maximum 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 electromechanical
impulse counter. The F1 and F2 outputs provide two alternat-
ing low going pulses. The pulsewidth (t1) is set at 275 ms and the
time between the falling edges of F1 and F2 (t3) is approxi-
mately 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 maximum output fre-
quencies for F1 and F2 are shown in Table III.
The high-frequency CF output is intended to be used for com-
munications and calibration purposes. CF produces a 90 ms-wide
active high pulse (t4) at a frequency proportional 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 pulsewidth is 25 ms.
NOTE: When the high-frequency mode is selected, (i.e., SCF = 0,
S1 = S0 = 1), the CF pulsewidth is fixed at 18 µs. Therefore, t4 will
always be 18 µs, regardless of the output frequency on CF.
NO LOAD THRESHOLD
The ADE7755 also includes a “no load threshold” and “start-
up current” feature that will eliminate any creep effects in the
meter. The ADE7755 is designed to issue a minimum output
frequency on all modes except when SCF = 0 and S1 = S0 = 1.
The no-load detection threshold is disabled on 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 mini-
mum 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, an energy meter with a meter constant
of 100 imp/kWhr on F1 and 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 is equivalent to 1.7 W of
load or a start-up current of 8 mA at 220 V. IEC1036 states that
the meter must start up with a load current equal to or less than
0.4% Ib. For a 5A (Ib) meter, 0.4% Ib is equivalent to 20mA.
The start-up current of this design therefore satisfies the IEC
requirement. As illustrated from this example, the choice of
F1–F4 and the ratio of the stepper motor display will determine
the start-up current.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
24-Lead Shrink Small Outline Package
(RS-24)
0.328 (8.33)
0.318 (8.08)
24
0.311 (7.9)
0.301 (7.64)
1
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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