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CS5460A-BS 参数 Datasheet PDF下载

CS5460A-BS图片预览
型号: CS5460A-BS
PDF下载: 下载PDF文件 查看货源
内容描述: 单相双向功率/电能IC [Single Phase Bi-Directional Power/Energy IC]
分类和应用:
文件页数/大小: 54 页 / 879 K
品牌: CIRRUS [ CIRRUS LOGIC ]
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CS5460A  
b) The common-mode rejection performance of the  
CS5460A is sufficient within the frequency range  
over which the CS5460A performs A/D conver-  
sions. Addition of such common-mode caps can  
actually often degrade the common-mode rejec-  
tion performance of the entire voltage/current input  
networks. Therefore, choosing relatively small val-  
ues for (CV+, CV-, CI+, CI-) will provide necessary  
common-mode rejection at the much higher fre-  
quencies, and will allow the CS5460A to realize its  
CMRR performance in the frequency-range of in-  
terest.  
pressed in rads/s). Subtracting these two  
time-constants shows that after the voltage/current  
signals pass through their respective anti-aliasing  
filters, the sensed voltage signal will be delayed  
~0.329 µs more than the current signal. If metering  
a 60 Hz power system, this implies that the input  
voltage-sense  
signal  
will  
be  
delayed  
~0.007 degrees more than the delay imposed on  
the input current-sense signal. Note that when the  
PC[6:0] bits are set to their default setting of  
“0000000”, the internal filtering stages of the  
CS5460A will impose an additional delay on the  
fundamental frequency component of the 60Hz  
voltage signal of 0.0215 degrees, with respect to  
the current signal. The total difference between the  
delay on the voltage-sense fundamental and the  
current-sense fundamental will therefore be  
~0.286 degrees. But if the phase compensation  
bits are set to 1111111, the CS5460A will delay the  
voltage channel signal by an additional -0.04 de-  
grees, which is equivalent to shifting the voltage  
signal forward by 0.04 degrees. The total phase  
shift on the voltage-sense signal (with respect to  
the fundamental frequency) would then be  
~0.011 degrees ahead of the current-sense signal,  
which would therefore provide more close-  
ly-matched delay values between the volt-  
age-sense and current-sense signals. Adjustment  
of the PC[6:0] bits therefore can provide an effec-  
tive way to more closely match the delays of the  
voltage/current sensor signals, allowing for more  
commonly available R and C component values to  
be used in both of these filters.  
[Note that this discussion does not include correc-  
tion of phase-shifts caused by the voltage-sense  
transformer and current-sense transformer, al-  
though these phase-shifts should definitely be con-  
sidered in a real-life practical meter design.] On the  
current channel, using commonly available values  
for the components, RI+ and RI- can be set to  
470 . Then a value of CIdiff = 18 nF and a value of  
0.22 nF for CI- and CI- will yield a -3 dB cutoff fre-  
quency of 15341 Hz for the current channel. For  
the voltage channel, if RI+ and RI- are also set to  
470 , CVdiff = 18 nF, and CV- = CV- = 0.22 nF  
(same as current channel), the -3 dB cutoff fre-  
quency of the voltage channel’s input filter will be  
14870 Hz. The difference in the two cutoff frequen-  
cies is due to the difference in the input impedance  
between the voltage/current channels.  
If there is concern about the effect that the differ-  
ence in these two cutoff frequencies (and therefore  
the mis-match between the time-constants of the  
overall voltage/current input networks) would have  
on the accuracy of the power/energy registration, a  
non-standard resistor value for RV+ = RV- of (for ex-  
ample) 455 can be used. This would shift the  
(differential) -3 dB cutoff frequency of the voltage  
channel’s input filter (at the voltage channel inputs)  
to ~15370 Hz, which would cause the first-order  
time-constants of the voltage/current channel input  
filters to be closer in value.  
As a final note, tolerances of the R and C compo-  
nents that are used to build the two R-C filters  
should also be taken into consideration. A com-  
mon tolerance of 0.1% can vary the delay by as  
much as much as ~ 2.07 µs, which means that the  
difference between the delays of the voltage-sense  
and current-sense signals that is caused by these  
filters could vary by as much as ~ 4.1 µs, which is  
equivalent to a phase shift of ~ 0.089 degrees (at  
60 Hz). This in turn implies that our decision to ad-  
just the PC[6:0] bits (to shift the voltage signal for-  
ward by 0.04 degrees) could actually cause the  
voltage signal to be shifted by as much as  
~0.100 degrees ahead of the current signal.  
Thus, adjustment of the PC[6:0] bits to more close-  
ly match the two time-constants/delays may only  
be useful if a precise calibration operation can be  
Agreement between the voltage/current channel  
time-constants can also be obtained by adjusting  
the phase compensation bits, instead of using less  
commonly-available resistor/capacitor values  
(such as RI+ = RI- = 455 ). If the values of RI+ and  
RI- are again 470 , the first-order time-constants  
of the two R-C filters are estimated by taking the re-  
ciprocal of the -3 dB cutoff frequencies (when ex-  
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