GENERAL DESCRIPTION

The supervisory circuit of the ADM809-5L/ADM809-5S monitors the power supply voltage in microprocessor systems. It provides a reset output during power-up, power-down, and brownout conditions. On power-up, an internal timer holds reset asserted for 55 ms. This holds the microprocessor in a reset state until conditions have stabilized. The RESET output remains operational with VCC as low as 1 V. The ADM809-5L/ADM809-5S provide an active low reset signal (RESET).

The reset comparator features built-in glitch immunity, making it immune to fast transients on VCC. The ADM809-5L/ADM809-5S consume only 17 μA, making them suitable for low power, portable equipment.

FEATURES

Specified over temperature

Low power consumption: 17 μA

Precision voltage monitor: 3 V, 5 V options

Reset assertion down to 1 V VCC

30 ms minimum power-on reset

Logic low RESET output

Available in SOT-23 and SC70 packages

APPLICATIONS

Microprocessor systems

Computers

Controllers

Intelligent instruments

Automotive systems

ABSOLUTE MAXIMUM RATINGS

TA = 25°C, unless otherwise noted.

Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device  reliability.

ESD CAUTION

ESD(electrostatic discharge) sensitive device.

Chargeddevices and circuit boards can dischargewithout detection.Although this product featurespatented or proprietary protection circuitry,damagemay occur on devices subjected to high energy ESD.Therefore, proper ESD precautions should be taken toavoid performance degradation or loss of functionality,.

THEORY OF OPERATION

INTERFACING TO OUTPUT OF OTHER DEVICES  The ADM809-5L/ADM809-5S are designed to integrate with as many devices as possible and, therefore, have an output dependent on VCC. Because of this design approach, interfacing these devices to other devices is simplified.

ENSURING A VALID RESET OUTPUT DOWN TO VCC = 0 V

When VCC falls below 0.8 V, the ADM809-5L/ADM809-5S RESET no longer sinks current. A high impedance CMOS logic input connected to RESET may, therefore, drift to undetermined logic levels. To eliminate this problem, a 100 kΩ resistor should be connected from RESET to ground.

BENEFITS OF A VERY ACCURATE RESET THRESHOLD

In other microprocessor supervisory circuits, tolerances in supply voltages lead to an overall increase in RESET tolerance levels due to the deterioration of the RESET circuit power supply of the microprocessor. The possibility of a malfunction during  a power failure is greatly reduced because the ADM809-5L/ ADM809-5S can operate effectively even when there are large degradations of the supply voltages. Another advantage of the ADM809-5L/ADM809-5S series is its very accurate internal voltage reference circuit. These benefits combine to produce an exceptionally reliable voltage monitor circuit.

INTERFACING TO MICROPROCESSORS WITH MULTIPLE INTERRUPTS

In a number of cases, it is necessary to interface to many interrupts from different devices (for example, from thermal, attitude, and velocity sensors). The ADM809-5L/ADM809-5S can be easily integrated into existing interrupt-handling circuits or used as standalone devices.

Rev. B

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents orother rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.

For more detailed information, please refer to the datasheet.