ADE9078 low power mode for no voltage detection

Author : Zhen Zhu

In China, there is a requirement for full voltage loss detection for three-phase electricity meters. This requirement defines a full voltage loss condition as when the input voltage is all below the threshold and the current is greater than 5% of the rated current.

When a full voltage loss event occurs, the meter records the phase voltage, phase current, power factor, and active power. The meter is designed with dual power supplies. The primary power supply is based on the external power line voltage input, and the backup power supply is based on an external battery. When a full voltage loss event occurs, the AC/DC power supply stops working, and the battery-powered microcontroller sets the ADE9078 analog front end (AFE) to detect current.

Figure 1. Block diagram of the power supply circuit for an energy meter. This application note describes how to configure the ADE9078

to detect a total voltage loss event.

This section describes the power modes of the ADE9078. The ADE9078 has four power modes to switch between. Users can select different power modes to save power.

Table 1 shows the technical specifications of the different power modes.

Table 1. Power Consumption in Various Power ModesPower

Saving Mode 0 (PSM0) is a fully functional mode that consumes 12 mA. The user can set the PSM0 mode to read/write all registers in the ADE9078. PSM0 is suitable for the power line powered mode. Normally, the ADE9078 operates in PSM0 mode, which means that at least one phase of the voltage is powering the meter.

PSM1, PSM2, and PSM3 support low power tamper detection, which is required in China. Using these operating modes, the user can detect whether there is power tampering. In situations involving power tampering, batteries are usually used to power the ADE9078. The

tamper measurement mode PSM1 allows the user to quickly measure key parameters such as current rms (IRMS), voltage rms (VRMS), power, and reactive volt-amperes (VAR) with lower power consumption than PSM0. It uses a different calculation method than PSM0. These measurements are calculated in 20 ms. In IRMS measurement, PSM1 mode detection takes 40.5 ms with a dynamic range of 600:1 and achieves an accuracy of less than 0.2%. For power, PSM1 mode takes 40.5 ms with a dynamic range of 600:1 and achieves an accuracy of less than 0.2%.

In PSM2 mode of operation, the ADE9078 enters a low power state with only the internal low power comparator active. The low dropout regulator (LDO), analog-to-digital converter (ADC), digital signal processor (DSP), and crystal oscillator are all powered down. The input currents IA, IB, and IC are compared to the user selected levels set in the PSM2_CFG register and an interrupt is generated and the pin is triggered if any current exceeds the threshold . The time taken to detect the peak current is determined by the user and is set in the LPLINE[4:0] bits of the PSM2_CFG register. The measurement cycle time is (LPLINE[4:0] + 4)/50 seconds. When the signal on a current channel is greater than the peak value for more than LPLINE[4:0] + 1 times, the ADE9078 indicates that a tampering condition has been detected. The maximum allowed value of LPLINE[4:0] is 0x0A.

PSM3 is an idle mode, which means that all functions inside the ADE9078 are shut down and the current consumed is less than 1 µA.

The PM0 and PM1 pins (PMx) control the PSMx mode, where x refers to PSM0 to PSM3.

Table 2 shows the PMx states and the associated PSMx modes.

Table 2. PMx States and Associated PMx Modes

Use the MCU's input/output pins to connect the PM0 and PM1 pins to select the power mode.

Hardware Solution

As shown in Figure 2, there are two power supplies in the meter: the AC/DC converter and the battery. They are switched by two diodes. The MCU detects the voltage output of the AC/DC power supply. If there is no voltage output, all phases (A, B, and C) are powered off. In this case, the MCU starts the full voltage loss detection function. When one of the phases is powered on, the AC/DC power supply outputs voltage to power the meter. Otherwise, the AC/DC is turned off, and the input/output pin triggers a low voltage to notify the MCU that a full voltage loss condition has occurred and the battery is supplying power. In this case, the MCU and ADE9078 enter low power mode.

Figure 2. Power Switching Circuit Block Diagram

Figure 3 shows the wiring requirements for the full voltage loss detection function between the MCU and the ADE9078. If a full voltage loss event occurs, the MCU will put the ADE9078 into a low power mode through the PM0 and PM1 pins.

Figure 3. Hardware wiring and software program between MCU and ADE9078 for full voltage loss detection function

Figure 4 shows the steps for total voltage loss detection.

Figure 4. Software routine for no voltage detection

PSM2_CFG is the configuration register for PSM2 mode and is set during the initialization of the ADE9078. For example, if the rated current is 10 A, the current transformer ratio is 2500:1, and the load resistance is 12.5 Ω, then at 5% of the rated current, the dynamic ratio of the peak value is: The



PKDET_LVL bits (Register 0x4B8, Bits [8:5]) are used to configure the low power comparator peak current detection level.

Table 3 shows the meaning of the settings.

Table 3. PSM2 Current Peak Detection Thresholds

When PSM2_CFG[8:5] is set to 3, it means the threshold level is 400:1.

LPLINE[4:0] is set to 1, so the measurement period of PSM2 mode is (1 + 4)/50 = 100 ms.

When initializing the ADE9078, set the PSM2_CFG register (Register 0x4B8) to 0x31.

Power Calculation

When power tampering is detected, the ADE9078 consumes the maximum current. The MCU sets the ADE9078 to PSM1 mode to read the effective value and power value for event recording. The power consumption of the ADE9078 in each link is as follows:

•PSM3 mode: 60 s × 2 μA = 120 μA
•PSM2 mode: 100 ms × 200 μA = 20 μA
•PSM1 mode: 40.5 ms × 9 mA = 364.5 μA

The total power consumption is: 120 + 20 + 364.5 = 504.5 μA. If power tampering continues for 7 days, the power consumption will be:


When power tampering is not detected, the ADE9078 consumes the minimum current. The ADE9078 does not enter PSM1 mode because there is no need to record effective values. The power consumption of the ADE9078 in each phase is as follows:

• PSM3 mode: 60 s × 2 μA = 120 μA
• PSM2 mode: 100 ms × 200 μA = 20 μA

The total power consumption is 120 + 20 = 140 μA. If this situation continues for 7 days, the power consumption will be:

The current mainstream external battery capacity is 1.2 Ah; therefore , even if power theft occurs, it is easy to meet the power consumption requirements of the ADE9078.

In both PSM2 and PSM3 modes, AVDDOUT and DVDDOUT are powered down. When entering PSM1 mode from PSM2 or PSM3 mode, AVDDOUT and DVDDOUT are powered up. Figure 5 shows the actual measurement results on the ADE9078 reference meter.

Figure 5. Power-up sequence for entering PSM1 mode

When the PM1 pin is set low, the PM0 pin is set high, and both pins reach a regulated voltage, AVDDOUT and DVDDOUT start to rise from 0 V, and the ADE9078 enters PSM1 mode.

1. Another test measures the time consumed by tamper detection in PSM2 mode. LPLINE[4:0] is set to 1. Ideally, if a tamper event occurs, the pins are triggered 100 ms after entering PSM2 mode . Figure 6 shows the test results of the ADE9078 reference meter.

It took 97.4 ms from entering PSM2 mode to trigger the pin. Set low when power theft is detected . Summary

ADE9078 is a newly designed metering AFE with high dynamic range and high accuracy. It provides four power modes with the lowest power consumption of 1 μA. ADE9078 consumes only 1.412 mAh energy at most in the state of total voltage loss, which is much lower than the battery capacity of 1.2 Ah. ADE9078 can be used to detect total voltage loss, even if this condition lasts for 7 days.