参数资料
| 型号： | EVAL-ADE7763ZEB |
| 厂商： | Analog Devices Inc |
| 文件页数： | 21/56页 |
| 文件大小： | 0K |
| 描述： | BOARD EVALUATION FOR ADE7763 |
| 标准包装： | 1 |
| 主要目的： | 电源管理，电度表/功率表 |
| 已用 IC / 零件： | ADE7763 |
| 已供物品： | 板 |
| 相关产品： | ADE7763ARSZRLDKR-ND - IC ENERGY METERING 1PHASE 20SSOP ADE7763ARSZRLCT-ND - IC ENERGY METERING 1PHASE 20SSOP ADE7763ARSZ-ND - IC ENERGY METERING 1PHASE 20SSOP ADE7763ARSZRLTR-ND - IC ENERGY METERING 1PHASE 20SSOP |
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Data Sheet
Antialias Filter
to the modulator. This filter prevents aliasing, which is an
artifact of all sampled systems. Aliasing means that frequency
components in the input signal to the ADC that are higher than
half the sampling rate of the ADC appear in the sampled signal
at a frequency below half the sampling rate. Figure 41 illustrates
the effect. Frequency components (shown as arrows) above half
the sampling frequency (also known as the Nyquist frequency,
i.e., 447 kHz) are imaged or folded back down below 447 kHz.
ADE7763
Reference Circuit
circuitry. The nominal reference voltage at the REF IN/OUT pin is
2.42 V. This is the reference voltage used for the ADCs. However,
Channel 1 has three input range options 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 ? and ? of the nominal value by using an internal
OUTPUT
This happens with all ADCs, regardless of the architecture. In
the example shown, only frequencies near the sampling
MAXIMUM
LOAD = 10 μ A
IMPEDANCE
6k ?
REF IN/OUT
frequency, i.e., 894 kHz, move into the band of interest for
metering, i.e., 40 Hz to 2 kHz. This allows the use of a very
simple LPF (low-pass filter) to attenuate high frequency (near
PTAT
60 μ A
2.5V
1.7k ?
2.42V
900 kHz) noise, and it prevents distortion in the band of interest.
For conventional current sensors, a simple RC filter (single-pole
12.5k ?
12.5k ?
LPF) with a corner frequency of 10 kHz produces an attenuation
of approximately 40 dB at 894 kHz—see Figure 41. The 20 dB
per decade attenuation is usually sufficient to eliminate the effects
of aliasing for conventional current sensors; however, for a di/dt
12.5k ?
12.5k ?
REFERENCE INPUT
TO ADC CHANNEL 1
(RANGE SELECT)
2.42V, 1.21V, 0.6V
sensor such as a Rogowski coil, the sensor has a 20 dB per decade
gain. This neutralizes the –20 dB per decade attenuation
produced by one simple LPF. Therefore, when using a di/dt
sensor, care should be taken to offset the 20 dB per decade gain.
One simple approach is to cascade two RC filters to produce the
–40 dB per decade attenuation.
ALIASING EFFECTS
SAMPLING
Figure 42. Reference Circuit Output
The REF IN/OUT pin can be overdriven by an external source such as
a 2.5 V reference. Note that the nominal reference value supplied
to the ADCs is now 2.5 V, not 2.42 V, which increases the
nominal analog input signal range by 2.5/2.42 × 100% = 3% or
from 0.5 V to 0.5165 V.
The voltage of the ADE7763 reference drifts slightly with changes
in temperature—see Table 1 for the temperature coefficient
IMAGE
FREQUENCIES
FREQUENCY
specification (in ppm/°C). The value of the temperature drift
varies from part to part. Because the reference is used for the
ADCs in both Channels 1 and 2, any x% drift in the reference
0
2 447 894
FREQUENCY (kHz)
Figure 41. ADC and Signal Processing in Channel 1 Outline Dimensions
results in 2x% deviation in the meter accuracy. The reference
drift that results from a temperature change is usually very
small, typically much smaller than the drift of other components
on a meter. However, if guaranteed temperature performance is
(1)
Code ( ADC ) = 3.0492 ×
× 262,144
ADC Transfer Function
The following expression relates the output of the LPF in the
Σ -? ADC to the analog input signal level. Both ADCs in the
ADE7763 are designed to produce the same output code for the
same input signal level.
V IN
V OUT
Therefore, with a full-scale signal on the input of 0.5 V and an
internal reference of 2.42 V, the ADC output code is nominally
165,151, or 0x2851F. The maximum code from the ADC is
±262,144; this is equivalent to an input signal level of ±0.794 V.
However, for specified performance, do not exceed the 0.5 V
needed, use an external voltage reference. Alternatively, the
meter can be calibrated at multiple temperatures. Real-time
compensation can be achieved easily by using the on-chip
temperature sensor.
CHANNEL 1 ADC
Channel 1. In waveform sampling mode, the ADC outputs a
signed, twos complement, 24-bit data-word at a maximum of
27.9 kSPS (CLKIN/128). With the specified full-scale analog
input signal of 0.5 V (or 0.25 V or 0.125 V—see the Analog
Inputs section), the ADC produces an output code that is
approximately between 0x28 51EC (+2,642,412d) and
full-scale input signal level.
Rev. C | Page 21 of 56
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