ADE7758 Ver la hoja de datos (PDF) - Analog Devices
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ADE7758 Datasheet PDF : 72 Pages
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ADE7758
THEORY OF OPERATION
ANTIALIASING FILTER
This filter prevents aliasing, which is an artifact of all sampled
systems. Input signals with frequency components higher than
half the ADC sampling rate distort the sampled signal at a fre-
quency below half the sampling rate. This happens with all ADCs,
regardless of the architecture. The combination of the high
sampling rate ∑-Δ ADC used in the ADE7758 with the relatively
low bandwidth of the energy meter allows a very simple low-
pass filter (LPF) to be used as an antialiasing filter. A simple RC
filter (single pole) with a corner frequency of 10 kHz produces
an attenuation of approximately 40 dB at 833 kHz. This is usually
sufficient to eliminate the effects of aliasing.
ANALOG INPUTS
The ADE7758 has six analog inputs divided into two channels:
current and voltage. The current channel consists of three pairs
of fully differential voltage inputs: IAP and IAN, IBP and IBN,
and ICP and ICN. These fully differential voltage input pairs
have a maximum differential signal of ±0.5 V. The current
channel has a programmable gain amplifier (PGA) with possible
gain selection of 1, 2, or 4. In addition to the PGA, the current
channels also have a full-scale input range selection for the ADC.
The ADC analog input range selection is also made using the
gain register (see Figure 38). As mentioned previously, the
maximum differential input voltage is ±0.5 V. However, by
using Bit 3 and Bit 4 in the gain register, the maximum ADC
input voltage can be set to ±0.5 V, ±0.25 V, or ±0.125 V on the
current channels. This is achieved by adjusting the ADC reference
(see the Reference Circuit section).
Figure 36 shows the maximum signal levels on the current
channel inputs. The maximum common-mode signal is
±25 mV, as shown in Figure 37.
V1 + V2
+500mV
VCM
–500mV
DIFFERENTIAL INPUT
V1 + V2 = 500mV MAX PEAK
COMMON-MODE
±25mV MAX
VCM
IAP, IBP,
OR ICP
V1
V2 IAN, IBN,
OR ICN
Figure 36. Maximum Signal Levels, Current Channels, Gain = 1
The voltage channel has three single-ended voltage inputs: VAP,
VBP, and VCP. These single-ended voltage inputs have a
maximum input voltage of ±0.5 V with respect to VN. Both the
current and voltage channel have a PGA with possible gain
selections of 1, 2, or 4. The same gain is applied to all the inputs
of each channel.
Figure 37 shows the maximum signal levels on the voltage
channel inputs. The maximum common-mode signal is
±25 mV, as shown in Figure 36.
Data Sheet
V2
+500mV
VCM
–500mV
SINGLE-ENDED INPUT
±500mV MAX PEAK
COMMON-MODE
±25mV MAX
VAP, VBP,
OR VCP
V2 VN
VCM
AGND
Figure 37. Maximum Signal Levels, Voltage Channels, Gain = 1
The gain selections are made by writing to the gain register.
Bit 0 to Bit 1 select the gain for the PGA in the fully differential
current channel. The gain selection for the PGA in the single-
ended voltage channel is made via Bit 5 to Bit 6. Figure 38
shows how a gain selection for the current channel is made
using the gain register.
GAIN[7:0]
IAP, IBP, ICP
VIN
GAIN (K)
SELECTION
K × VIN
IAN, IBN, ICN
Figure 38. PGA in Current Channel
Figure 39 shows how the gain settings in PGA 1 (current
channel) and PGA 2 (voltage channel) are selected by various
bits in the gain register.
GAIN REGISTER1
CURRENT AND VOLTAGE CHANNEL PGA CONTROL
76 54 32 10
0 0 0 0 0 0 0 0 ADDRESS: 0x23
INTEGRATOR ENABLE
0 = DISABLE
1 = ENABLE
PGA 2 GAIN SELECT
00 = ×1
01 = ×2
10 = ×4
RESERVED
PGA 1 GAIN SELECT
00 = ×1
01 = ×2
10 = ×4
CURRENT INPUT FULL-SCALE SELECT
00 = 0.5V
01 = 0.25V
10 = 0.125V
1REGISTER CONTENTS SHOW POWER-ON DEFAULTS
Figure 39. Analog Gain Register
Bit 7 of the gain register is used to enable the digital integrator
in the current signal path. Setting this bit activates the digital
integrator (see the DI/DT Current Sensor and Digital Integrator
section).
Rev. E | Page 18 of 72
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