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MAX71020
Single-Chip Electricity Meter AFE
× 360 t delay × f × 360 ?
t delay ?
For a standard single-phase application with tamper sen-
sor in the neutral path, two current inputs are configured
for differential mode, using the pin pairs IAP-IAN and IBP-
IBN. The MAX71020 uses two locally connected current
sensors via IAP-IAN and IBP-IBN for this configuration.
The VA pin is typically connected to the phase voltage via
resistor-dividers.
The MAX71020 adds the ability to sample a second
phase voltage (applied at the VB pin), which makes it
suitable for meters with two voltage and two current sen-
sors, such as meters implementing Equation 2 for dual-
phase operation (P = VA x IA + VB x IB).
Table 1 summarizes the AFE input configuration.
Delay Compensation
When measuring the energy of a phase (i.e., Wh and
VARh) in a service, the voltage and current for that phase
must be sampled at the same instant. Otherwise, the
phase difference, φ , introduces errors.
φ
= =
T
where f is the frequency of the input signal, T = 1/f and
t delay is the sampling delay between current and voltage.
Table 1. ADC Input Configuration
Traditionally, sampling is accomplished by using two
ADCs per phase (one for voltage and the other one for
current) controlled to sample simultaneously. Maxim
Integrated’s Single Converter Technology?, however,
exploits the 32-bit signal processing capability of its CE
to implement “constant delay” allpass filters. The allpass
filter corrects for the conversion time difference between
the voltage and the corresponding current samples that
are obtained with a single multiplexed ADC.
The constant delay allpass filter provides a broadband
delay 360 N - θ, which is precisely matched to the differ-
ence in sample time between the voltage and the current
of a given phase. This digital filter does not affect the
amplitude of the signal, but provides a precisely con-
trolled phase response.
The ADC multiplexer samples the current first, immedi-
ately followed by sampling of the corresponding phase
voltage, thus the voltage is delayed by a phase angle
φ relative to the current. The delay compensation imple-
mented in the CE aligns the voltage samples with their
corresponding current samples by first delaying the cur-
rent samples by one full sample interval (i.e., 360 N ), then
routing the voltage samples through the allpass filter, thus
delaying the voltage samples by 360 N - θ, resulting in the
residual phase error between the current and its corre-
sponding voltage of θ - φ . The residual phase error is neg-
PIN
IAP
IAN
IBP
IBN
VA
VB
COMMENT
The ADC results are stored in register IA.
The ADC results are stored in register IB.
The ADC result is stored in register VA.
The ADC result is stored in register VB.
CK32
ligible, and is typically less than ±0.0015 N at 100Hz, thus it
does not contribute to errors in the energy measurements.
ADC Preamplifier
The ADC preamplifier is a low-noise differential amplifier
with a fixed gain of 8.9 available on the IAP and IAN cur-
rent-sensor input pins. It is provided only in versions of the
MAX71020 AFE configured for use with current shunts.
MULTIPLEXER FRAME
MUX DIV = 4 CONVERSIONS
SETTLE
MUX STATE
S
0
1
2
3
S
0
IA
VA
IB
VB
CROSS
MUX_SYNC
Figure 2. States in a Multiplexer Frame
Single Converter Technology is a registered trademark of Maxim Integrated Products, Inc.
Maxim Integrated
11
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相关代理商/技术参数
MAX71020AEUI+R 制造商:MAXIM 制造商全称:Maxim Integrated Products 功能描述:Single-Chip Electricity Meter AFE
MAX710C/D 功能描述:直流/直流开关转换器 3.3V/5V or Adjustable Step-Up Step-Down DC-DC Converters RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT
MAX710C/D DIE 制造商:Maxim Integrated Products 功能描述:
MAX710ESE 功能描述:直流/直流开关转换器 3.3/5V or Adjustable Step-Up Step-Down RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT
MAX710ESE+ 功能描述:直流/直流开关转换器 3.3/5V or Adjustable Step-Up Step-Down RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT
MAX710ESE+ 制造商:Maxim Integrated Products 功能描述:CONVERTOR DC/DC ((NW))
MAX710ESE+T 功能描述:直流/直流开关转换器 3.3/5V or Adjustable Step-Up Step-Down RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT
MAX710ESE-T 功能描述:直流/直流开关转换器 3.3/5V or Adjustable Step-Up Step-Down RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT