Multiple-Input Supervisor Control ICs

Usually, supervisory ICs operate with system processors, such as a microcontrollers,  microprocessors  or digital signal processors. Among the typical functions found in supervisory devices are:

  • A Reset generator activated either manually or by a voltage threshold.
  • A Fault output that indicates an error.
  • Monitoring and sequencing a power source to the system processor or memory.
  • Monitoring the voltage from regulated or unregulated power supplies or batteries.
  • Monitoring multiple system power supplies, including ±12V, +5V, +3.3V, etc.
  • Watchdog timer to protect against software problems of a power failure

Most supervisory ICs ensure that both the power supplies and software operate within specified voltage and time windows. In its most basic form, a supervisory IC compares a power supply voltage with a specific threshold. If the power source reaches that threshold, the supervisory IC generates a pulse that resets the system processor or sends out a Fault signal.

Basically, the voltage monitoring section of the supervisory IC includes a comparator and voltage reference. Many systems require multiple supply voltages that can be monitored with multiple devices, but some of the supervisory ICs can monitor two or more voltages. Typically, the number threshold voltages required in a system depends on the number of processor and peripheral power supplies.

Many supervisory ICs include a manual reset that allows the user to reset the circuit or control the supervisory circuit by another device.

The reset function of the supervisory IC may provide a power-on-reset (POR) to eliminate problems during power-up or a supply voltage sag. These problems can occur because of a slow-rising supply voltage, a supply voltage that exhibits noise or poor behavior during startup, or recovery from a sag. Typically, the reset circuit's voltage tolerance should not exceed ±2.7% over temperature.

Many supervisory ICs include undervoltage and overvoltage comparators with programmable thresholds. Inputs for these comparators can implement a windowed reset that warns if a particular voltage is either too high or too low.

Another common requirement for microprocessor-based systems is a watchdog timer that protects against improper software execution. Usually, the watchdog timer is a restartable timer whose output changes state on timeout, resetting the system processor or generating an interrupt.

To ensure the continuity of processor memory contents and other critical functions if a supply voltage is lost, many of the older supervisory circuits are able to switch the memory's power source to a backup battery.

Following are descriptions supervisory control ICs.

1. This dual supply supervisor monitors two independent ?48V supplies, including their fuses, and drives up to three opto-isolators to indicate status, in accordance with standard backplane specifications. Requiring only three non-critical resistors and opto-isolators, the IC replaces multiple voltage comparators, a voltage reference and several precision resistors.

The monitor features dual supply overvoltage and undervoltage detection circuits. The preset trip thresholds include overvoltage, undervoltage and undervoltage recovery that are guaranteed over temperature and meet or exceed common backplane specifications. Additional built-in circuitry detects the condition of supply fuses. Overvoltage and undervoltage detectors ignore fast supply transients, eliminating false detection.

Monitoring for each supply is independent of the condition of the other supply. The IC can be powered equally from either one or both supplies. This allows it to provide correct information at its outputs as long as at least one supply is functional, whether or not the fuses are intact.

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