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參數(shù)資料
| 型號： | EVAL-ADE7756EB |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Active Energy Metering IC with Serial Interface |
| 中文描述： | 有源電能計量IC串行接口 |
| 文件頁數(shù)： | 17/32頁 |
| 文件大?。?/td> | 347K |
| 代理商： | EVAL-ADE7756EB |
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REV. 0
ADE7756
–17–
Antialias Filter
Figure 21 also shows an analog low-pass filter (RC) on the input
to the modulator. This filter is present to prevent aliasing. Alias-
ing is an artifact of all sampled systems.
Figure 16 illustrates the effect, frequency components (arrows
shown in black) above half the sampling frequency (also known
as the Nyquist frequency, i.e., 447 kHz) is imaged or folded
back down below 447 kHz (arrows shown in grey). This will
happen with all ADCs no matter what the architecture is. In the
example shown it can be seen that only frequencies near the
sampling frequency, i.e., 894 kHz, will move into the band of
interest for metering, i.e., 40 Hz–2 kHz. This fact will allow us
to use a very simple LPF (Low-Pass Filter) to attenuate these
high frequencies (near 900 kHz) and so prevent distortion in the
band of interest. A simple RC filter (single-pole) with a corner
frequency of 10 kHz will produce an attenuation of approxi-
mately 40 dBs at 894 kHz—see Figure 15. This is sufficient to
eliminate the effects of aliasing.
FREQUENCY
–
kHz
ALIASING EFFECTS
0
447
894
2
IMAGE
FREQUENCIES
SAMPLING
FREQUENCY
Figure 16. ADC and Signal Processing in Channel 1
ADC Transfer Function
Below is an expression that relates the output of the LPF in the
sigma-delta ADC to the analog input signal level. Both ADCs in
the ADE7756 are designed to produce the same output code for
the same input signal level.
Code ADC
(
V
V
IN
REF
)
.
,
=
×
×
1 512
262 144
Therefore, with a full-scale signal on the input of 1 V, and an
internal reference of 2.4 V, the ADC output code is nominally
165,151 or 2851Fh. The maximum code from the ADC is
±
262,144, which is equivalent to an input signal level of
±
1.6 V.
However, for specified performance it is not recommended that
the full-scale input signal level of
±
1 V be exceeded.
Reference Circuit
Shown in Figure 17 is a simplified version of the reference output
circuitry. The nominal reference voltage at the REF
IN/OUT
pin
is 2.42 V. This is the reference voltage used for the ADCs in the
ADE7756. However, Channel 1 has three input range selections
that are selected by dividing down the reference value used for the
ADC in Channel 1. The reference value used for Channel 1 is
divided down to 1/2 and 1/4 of the nominal value by using an
internal resistor divider as shown in Figure 17.
1.7k
PTAT
REF
IN/OUT
2.42V
MAXIMUM
LOAD = 10 A
12.5k
12.5k
12.5k
12.5k
REFERENCE INPUT TO ADC
CHANNEL 1 (RANGE SELECT)
2.42V, 1.21V, 0.6V
2.5V
OUTPUT IMPEDANCE
4k
60 A
Figure 17. Reference Circuit Output
The REF
IN/OUT
pin can be overdriven by an external source,
e.g., an external 2.5 V reference. Note that the nominal refer-
ence value supplied to the ADCs is now 2.5 V, not 2.42 V. This
has the effect of increasing the nominal analog input signal
range by 2.5/2.42
×
100% = 3%, or from 1 V to 1.03 V.
The voltage of ADE7756 reference drifts slightly with temperature
—see ADE7756 Specifications for the temperature coefficient
specification (in ppm/
°
C). The value of the temperature drift varies
from part to part. On A-grade parts, the maximum temperature
drift is not guaranteed. Since the reference is used for the ADCs
in both Channel 1 and 2, any x% drift in the reference will result
in 2x% deviation of the meter accuracy. The reference drift
resulting from temperature changes is usually very small and it is
typically much smaller than the drift of other components on a
meter. However, if guaranteed temperature performance is
needed, one needs to use an external voltage reference or to use
B-grade parts. Alternatively, the meter can be calibrated at
multiple temperatures. Real-time compensation can be easily
achieved using the on the on-chip temperature sensor.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
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| EVAL-ADE7758ZEB | 功能描述:BOARD EVAL FOR AD7758 RoHS:是 類別:編程器，開發(fā)系統(tǒng) >> 評估演示板和套件 系列:* 標準包裝:1 系列:PSoC® 主要目的:電源管理，熱管理 嵌入式:- 已用 IC / 零件:- 主要屬性:- 次要屬性:- 已供物品:板，CD，電源 |
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