ADE7755AN-REF Analog Devices, ADE7755AN-REF Datasheet - Page 16

• Manufacturer Part Number: ADE7755AN-REF
• Description: Energy Metering IC with Pulse Output
• Manufacturer: Analog Devices

ADE7755
S1
0
0
1
1
When selecting a suitable F
frequency output at I
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 (F
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, F
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 (t
time between the falling edges of F1 and F2 (t
mately half the period of F1 (t
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.
Table VI. F1 and F2 Frequency with Half-Scale AC Inputs
S0
0
1
0
1
2
F
1.7
3.4
6.8
13.6
(3.4 Hz—see Table II) is selected for this design.
1–4
MAX
Frequency on F1 and F2
CH1 and CH2 Half-Scale AC Inputs
0.085 Hz
0.17 Hz
0.34 Hz
0.68 Hz
(maximum load) with a meter constant
1–4
1–4
). For example, if a meter with a
frequency for a meter design, the
2
). If, however, the period of
1
0.301 (7.64)
0.311 (7.9)
) is set at 275 ms and the
0.078 (1.98)
0.068 (1.73)
0.008 (0.203)
0.002 (0.050)
3
24-Lead Shrink Small Outline Package
) is approxi-
24
1
PIN 1
Dimensions shown in inches and (mm)
0.0256
(0.65)
BSC
OUTLINE DIMENSIONS
0.328 (8.33)
0.318 (8.08)
0.015 (0.38)
0.010 (0.25)
(RS-24)
–16–
SEATING
0.066 (1.67)
PLANE
13
12
0.07 (1.78)
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 (t
power. The CF output frequencies are given in Table IV. As in
the case of F1 and F2, if the period of CF (t
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 ms. Therefore, t
always be 18 ms, 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 F
Table II). For example, an energy meter with a meter constant
of 100 imp/kWhr on F1 and F2 using F
output frequency at F1 or F2 would be 0.0014% of 3.4 Hz or
4.76 ¥ 10
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.
0.205 (5.207)
0.212 (5.38)
0.009 (0.229)
0.005 (0.127)
–5
Hz. This would be 3.05 ¥ 10
8°
0°
4
) at a frequency proportional to active
0.022 (0.559)
0.037 (0.94)
1–4
frequency selections (see
–3
2
Hz at CF (64 ¥ F1 Hz).
(3.4 Hz), the maximum
5
) falls below 180 ms,
REV. 0
4
will