Utility Metering Design CenterBlock Diagram
Low Voltage Detection Solutions
Low voltage detection circuits can be implemented adding stand alone supervisor devices to the application, see the link below for a list of such devices:
System Supervisors
or by selecting a PIC© microcontroller that already integrates a BORmodule (see below) and possibly a PLVDmodule.
See the link below for a list of PIC© microcontrollers that offer such functionalities:
PIC© Microcontrollers with Integrated System Supervisors
PICmicro©BOR modules
The BOR (Brown-out Reset) module is based on an internal voltage reference circuit. The main purpose of the BOR module is to generate a device RESET when a brown-out condition occurs. Brown-out conditions can be caused by glitches on the AC mains (i.e., missing waveform portions of the AC cycles due to bad power transmission lines), or voltage sags due to excessive current draw when a large load is energized.
Figure 1
See the link below for a short presentation on PICmicro©reset circuits:
PICmicro© LVD modules
The LVD module is applicable to battery operated applications. As the battery drains its energy, the battery voltage slowly drops. The battery source impedance also increases as it loses energy. The LVD module is used to detect when the battery voltage (and therefore, the VDD of the device) drops below a threshold, which is considered near the end of battery life for the application. This allows the application to gracefully shutdown its operation. The LVD module uses an internal reference voltage for comparison. The threshold voltage, VLVD, is programmable during run-time.Figure 2 shows a possible application battery voltage curve.
Over time, the device voltagedecreases. When the device voltage equals voltage VLVD, the LVD logic generates an interrupt. This occurs at time TA.
The application software then has until the device voltage is no longer in valid operating range to shutdown the system. Voltage point VB is the minimum valid operatingvoltage specification. This gives a time TB.
The total time for shutdown is TB – TA.
Figure 2
A comparator uses an internallygenerated reference voltage as the set point. When the selected tap output of the device voltageis lower than the reference voltage, the LVDIF bit (IFS2<10>) is set.Each node in the resistor divider represents a “trip point” voltage.
This voltage is softwareprogrammable to any one of 16 values
Figure 3 shows the block diagram for the LVD module.
Figure 3
You can learn more on specific PICmicro© models LVD circuit implementations by referring to the respective device datasheet.