Supervisory Circuits with Watchdog and

Manual Reset in 5-Lead SC70 and SOT-23

Preliminary Technical Data

ADM823/ADM824/ADM825

Rev.PrB

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FEATURES

Precision 2.5 V to 5 V power supply monitor

7 reset threshold options: 2.19 V to 4.63 V

140 ms (min) reset timeout

Watchdog timer with 1.6s timeout (ADM823, ADM824)

Manual reset input (ADM823, ADM825)

Push-pull output stages:

RESET (ADM823)

RESET, RESET (ADM824/ADM825)

Low power consumption (3 µA)

Power supply glitch immunity

Specified over automotive temperature range

5-lead SC70 and SOT-23 packages

APPLICATIONS

Microprocessor systems

Computers

Controllers

Intelligent instruments

Portable equipment

FUNCTIONAL BLOCK DIAGRAM

ADM823

MR

GND

WDI

RESET

RESET

GENERATOR

WATCHDOG

DETECTOR

DEBOUNCE

Figure 1.

GENERAL DESCRIPTION

The ADM823/ADM824/ADM825 are supervisory circuits

which monitor power supply voltage levels and code execution

integrity in microprocessor-based systems. As well as providing

power on reset signals, an on-chip watchdog timer can reset the

microprocessor if it fails to strobe within a preset timeout

period. A reset signal can also be asserted by means of an

external push-button, through a manual reset input. The three

parts feature different combinations of watchdog input, manual

reset input and output stage configuration, as shown in Table 1.

Each part is available in a choice of seven reset threshold

options ranging from 2.19 V to 4.63 V. The reset and watchdog

timeout periods are fixed at 140 ms (min) and 1.6s (typ),

respectively.

The ADM823/ADM824/ADM825 are available in 5-lead SC70

and SOT-23 packages and typically consume only 3 µA, making

them suitable for use in low power portable applications.

Table 1. Selection Table

Output Stage

Part No.

Watchdog Timer

Manual Reset

RESET

RESET

ADM823

Yes

Yes

Push-Pull

–

ADM824

Yes

–

Push-Pull

Push-Pull

ADM825

–

Yes

Push-Pull

Push-Pull