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ADE7761AARS-REF 参数 Datasheet PDF下载

ADE7761AARS-REF图片预览
型号: ADE7761AARS-REF
PDF下载: 下载PDF文件 查看货源
内容描述: 电能计量IC ,带有片上故障和中性丢失检测 [Energy Metering IC with On-Chip Fault and Missing Neutral Detection]
分类和应用:
文件页数/大小: 24 页 / 527 K
品牌: ADI [ ADI ]
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ADE7761A  
DIGITAL-TO-FREQUENCY CONVERSION  
The output frequency on CF can be up to 2048 times higher  
than the frequency on F1 and F2. This higher output frequency  
is generated by accumulating the instantaneous active power  
signal over a much shorter time while converting it to a frequency.  
This shorter accumulation period means less averaging of the  
cos(2ωt) component. As a consequence, some of this instantaneous  
power signal passes through the digital-to-frequency conversion.  
This is not a problem in the application.  
As previously described, the digital output of the low-pass filter  
after multiplication contains the active power information.  
However, because this LPF is not an ideal brick wall filter  
implementation, the output signal also contains attenuated  
components at the line frequency and its harmonics, that is,  
cos(hωt), where h = 1, 2, 3, …, and so on. The magnitude  
response of the filter is given by  
1
Where CF is used for calibration purposes, the frequency  
should be averaged by the frequency counter, which removes  
any ripple. If CF is being used to measure energy, such as in a  
microprocessor-based application, the CF output should also be  
averaged to calculate power. Because the outputs, F1 and F2,  
operate at a much lower frequency, a lot more averaging of the  
instantaneous active power signal is carried out. The result is a  
greatly attenuated sinusoidal content and a virtually ripple-free  
frequency output.  
H( f ) =  
(6)  
1 = ( f /4.5Hz)2  
For a line frequency of 50 Hz, this gives an attenuation of the 2ω  
(100 Hz) component of approximately −26.9 dB. The dominating  
harmonic is at twice the line frequency, cos(2ωt), due to the  
instantaneous power signal.  
F1  
TRANSFER FUNCTION  
Frequency Outputs F1 and F2  
DIGITAL-TO-  
FREQUENCY  
F1  
F2  
V
The ADE7761A calculates the product of two voltage signals  
(on Channel 1 and Channel 2) and then low-pass filters this  
product to extract active power information. This active power  
information is then converted to a frequency. The frequency  
information is output on F1 and F2 in the form of active high  
pulses. The pulse rate at these outputs is relatively low, for  
example, 0.34 Hz maximum for ac signals with S0 = S1 = 0  
(see Table 8). This means that the frequency at these outputs is  
generated from active power information accumulated over a  
relatively long period. The result is an output frequency that is  
proportional to the average active power. The averaging of the  
active power signal is implicit to the digital-to-frequency  
conversion. The output frequency or pulse rate is related to  
the input voltage signals by  
TIME  
MULTIPLIER  
FOUT  
DIGITAL-TO-  
FREQUENCY  
LPF  
I
CF  
LPF TO EXTRACT  
ACTIVE POWER  
(DC TERM)  
TIME  
0
ω
2ω  
FREQUENCY (Rad/s)  
INSTANTANEOUS ACTIVE POWER SIGNAL (FREQUENCY DOMAIN)  
Figure 27. Active Power to Frequency Conversion  
Figure 27 shows the instantaneous active power signal output of  
the LPF, which still contains a significant amount of instantaneous  
power information, cos(2ωt). This signal is then passed to the  
digital-to-frequency converter, where it is integrated (accumulated)  
over time to produce an output frequency. This accumulation of  
the signal suppresses or averages out any non-dc components in  
the instantaneous active power signal. The average value of a  
sinusoidal signal is zero. Therefore, the frequency generated by  
the ADE7761A is proportional to the average active power.  
5.70×Gain×V1rms ×V2rms × F  
14  
F F Frequency =  
(7)  
1
2
2
VREF  
where:  
F1 F2 Frequency is the output frequency on F1 and F2 (Hz).  
V1rms is the differential rms voltage signal on Channel 1 (V).  
V2rms is the differential rms voltage signal on Channel 2 (V).  
Figure 27 also shows the digital-to-frequency conversion for  
steady load conditions: constant voltage and current. As can be  
seen in Figure 27, the frequency output CF varies over time,  
even under steady load conditions. This frequency variation is  
primarily due to the cos(2ωt) component in the instantaneous  
active power signal.  
Gain is 1 or 16, depending on the PGA gain selection made  
using the logic input PGA.  
V
REF is the reference voltage (2.5 V 8%) (V).  
1–4 is one of four possible frequencies selected by using the  
logic inputs S0 and S1 (see Table 6).  
F
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