AD71056ARZ Analog Devices Inc, AD71056ARZ Datasheet - Page 15

• Manufacturer Part Number: AD71056ARZ
• Description: IC,Power Metering,CMOS,SOP,16PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of AD71056ARZ

• Input Impedance: 320 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.8V
• Current - Supply: 5mA
• Voltage - Supply: 4.75 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.154", 3.90mm Width)
• Meter Type: Single Phase
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The energy consumed during an integration period is given by
For the purpose of calibration, this integration time can be as
long as 10 seconds to 20 seconds to accumulate enough pulses
to ensure correct averaging of the frequency. In normal operation,
the integration time can be reduced to one or two seconds,
depending, for example, on the required update rate of a
display. With shorter integration times on the MCU, the
amount of energy in each update can still have some small
amount of ripple, even under steady load conditions. However,
over a minute or more the measured energy has no ripple.
Power Measurement Considerations
Calculating and displaying power information always has some
associated ripple that depends on the load as well as the integration
period used in the MCU to determine average power. For
example, at light loads, the output frequency may be 10 Hz.
With an integration period of two seconds, only about 20 pulses
are counted. The possibility of missing one pulse always exists,
because the output frequency of the AD71056 is running
asynchronously to the MCU timer. This results in a 1-in-20, or
5%, error in the power measurement.
INTERNAL OSCILLATOR (OSC)
The nominal internal oscillator frequency is 450 kHz when
used with RCLKIN, with a nominal value of 6.2 kΩ. The
frequency outputs are directly proportional to the oscillator
frequency, thus RCLKIN must have low tolerance and low
temperature drift to ensure stability and linearity of the chip.
The oscillator frequency is inversely proportional to the
RCLKIN, as shown in Figure 27. Although the internal
oscillator operates when used with RCLKIN values between
5.5 kΩ and 20 kΩ, choosing a value within the range of the
nominal value, as shown in Figure 27, is recommended.
Energy
Figure 27. Effect of RCLKIN on Internal Oscillator Frequency (OSC)
490
480
470
460
450
440
430
420
410
400
=
Average
5.8
5.9
Power
6.0
×
6.1
Time
RESISTANCE (kΩ)
6.2
=
Counter
Time
6.3
6.4
×
Time
6.5
=
Counter
6.6
6.7
Rev. A | Page 15 of 20
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TRANSFER FUNCTION
Frequency Outputs F1 and F2
The AD71056 calculates the product of two voltage signals
(on Channel V1 and Channel V2) and then low-pass filters this
product to extract real power information. This real power
information is then converted to a frequency. The frequency
information is output on F1 and F2 in the form of active low
pulses. The pulse rate at these outputs is relatively low, for
example, 0.175 Hz maximum for ac signals with S0 = S1 = 0
(see Table 6). This means that the frequency at these outputs is
generated from real power information accumulated over a
relatively long period of time. The result is an output frequency
that is proportional to the average real power. The averaging of
the real power signal is implicit to the digital-to-frequency
conversion. The output frequency or pulse rate is related to the
input voltage signals by the following equation:
where:
Freq = output frequency on F1 and F2 (Hz).
V1
V2
V
f
Logic Input S0 and Logic Input S1 (see Table 5).
Table 5. f
S1
0
0
1
1
1
2
Example
In this example, with ac voltages of ±30 mV peak applied to
V1 and ±165 mV peak applied to V2, the expected output
frequency is calculated as
f
V1
V2
V
Note that if the on-chip reference is used, actual output
frequencies can vary from device to device due to the reference
tolerance of ±200 mV.
Freq
1…4
1…4
f
Values are generated using the nominal frequency of 450 kHz.
1…4
REF
REF
rms
rms
rms
rms
= one of four possible frequencies selected by using
= OSC/2
is a binary fraction of the internal oscillator frequency (OSC).
= the reference voltage (2.45 V ±200 mV) (V).
= 2.45 V (nominal reference value)
Freq
= differential rms voltage signal on Channel V1 (V).
= differential rms voltage signal on Channel V2 (V).
= 0.03/√2 V
= 0.165/√2 V
=
S0
0
1
0
1
494
1…4
=
.
494
75
19
Frequency Selection
2
Hz, S0 = S1 = 0
×
.
OSC Relation
OSC/2
OSC/2
OSC/2
OSC/2
75
×
. 0
×
03
2
V1
×
×
V
19
18
17
16
rms
. 0
. 2
REF
165
45
×
2
V2
2
×
rms
1
f
1
×
=
f
1
f
0.86
1.72
3.43
6.86
...
. 0
1
4
…
204
4
at Nominal OSC (Hz)
×
f
1
=
. 0
175
AD71056
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2