Analog Devices ADM9690AR Datasheet

Power Supply and Watchdog Timer

a

FEATURES
Precision Voltage Monitor (4.31 V)
Watchdog Timeout Monitor
Selectable Watchdog Timeout—0.75 ms, 1.5 ms,

12.5 ms, 25 ms

Two RESET Outputs

APPLICATIONS
Microprocessor Systems
Computers
Printers
Controllers
Intelligent Instruments

GENERAL DESCRIPTION

The ADM9690 contains a voltage monitoring comparator and a
watchdog timer monitor. It is designed to monitor the 5 V
power supply to a microprocessor and the microprocessor opera­tion via a watchdog function.

The voltage monitoring comparator monitors the voltage on
V

. If it drops outside tolerance, as will happen during a

MON

power-fail, two reset signals are generated. Both reset signals go
active (low) simultaneously. They will remain active while

is below the threshold, and for 50 ms (RESET(1)) or

V

MON

60 ms (RESET(2)) after V
old. RESET(1) is intended to provide a power-on reset signal
for the µP while RESET(2) is used to hold additional circuitry
in a reset state until the µP has regained control following a
power-up. The voltage monitoring circuitry remains operational
with V

as low as 2 V.

CC

climbs above the reset thresh-

MON

Monitoring Circuit

ADM9690

FUNCTIONAL BLOCK DIAGRAM

V

CC

V

MON

4.31V

OSC SEL1

OSC SEL2

WATCHDOG
INPUT (WDI)

WATCHDOG

TIMEBASE

WATCHDOG
TRANSITION

DETECTOR

The watchdog timer monitoring circuit is designed to monitor
the activity on the WDI input. This input is normally connected
to an output line on the µP. Its function is to check that the
microprocessor has not stalled in an infinite loop. If there is a
period of inactivity for the watchdog timeout period, both reset
outputs are activated. As above, RESET(1) remains low for
50 ms while RESET(2) remains low for an additional 10 ms.
The watchdog timer is restarted when RESET(1) goes inactive.
The actual watchdog timeout period is adjustable using two
select inputs SEL1 and SEL2.

The ADM9690 is available in an 8-lead SOIC package. It is
specified over the industrial temperature range.

GND

ADM9690

RESET(1)

TIMER

RESET(2)

TIMER

RESET(1)

RESET(2)

REV. A

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reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
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Fax: [phone] © Analog Devices, Inc., 2000

ADM9690–SPECIFICATIONS

(VCC = Full Operating Range. TA = T

MIN

to T

unless otherwise noted)

MAX

Parameter Min Typ Max Units Test Conditions/Comments

VCC OPERATING VOLTAGE RANGE 4.3 5.5 V

SUPPLY CURRENT 55 100 µA

RESET AND WATCHDOG TIMER

Reset Voltage Threshold 4.2 4.31 4.42 V V

Falling TA = 0°C to +70°C

MON

Reset Threshold Hysteresis 30 mV
Reset Timeout Delay (t1) 50 75 ms Figure 7, 8
RESET(2) Timeout Delay (t2) 10 15 ms Figure 7, 8

WATCHDOG TIMEOUT PERIOD (TWD) 0.4 0.75 1.28 ms SEL2 = 0, SEL1 = 0

1.0 1.5 2.4 ms SEL2 = 0, SEL1 = 1

9.0 12.5 19 ms SEL2 = 1, SEL1 = 0
18 25 38 ms SEL2 = 1, SEL1 = 1

WDI INPUT PULSEWIDTH 100 ns V

RESET(1)/(2) Output Voltage 0.1 0.4 V I

0.3 0.4 V I

0.45 0.7 V I

3.5 V I

= 0.4, VIH = 3.5 V

IL

= 3.2 mA

SINK

= 10 mA,

SINK

= 15 mA,

SINK

SOURCE

WDI INPUT THRESHOLD

Logic Low 0.8 V 150 ns Pulse
Logic High 3.5 V 150 ns Pulse
WDI Input Current 1.2 5 µA WDI = V

–5 –1.2 µA WDI = 0 V

SEL1/2 Input Current –1 +1 µA SEL = V

–10 –5 10 µA SEL = 0 V

Specifications subject to change without notice.

= 1 µA

CC

CC

–2–

REV. A