ADM694 Analog Devices, ADM694 Datasheet - Page 6

• Manufacturer Part Number: ADM694
• Manufacturer: Analog Devices

Specifications of ADM694

• Batt-backup-flg: Yes
• Product Description: µP Supervisor w/ Backup Battery Switching, Watchdog, Power Fail Flag, 4.65V Vth, 100mA Iout
• Reset Threshold (v): 4.65
• Min Reset Timeout (ms): 140
• Reset Output-stage: Active-Low/Push-Pull
• Backup-battery Switch: Yes
• Chip Enable Gating: ---
• Typ Watchdog Timeout (ms): 100,1600,adj.
• Package: DIP
• Us Price 1000-4999: n/a

ADM690–ADM695
POWER FAIL RESET OUTPUT
RESET is an active low output which provides a RESET signal
to the Microprocessor whenever V
V
low. The nominal reset voltage threshold is 4.65 V (ADM690/
ADM691/ADM694/ADM695) or 4.4 V (ADM692/ADM693).
On power-up RESET will remain low for 50 ms (200 ms for
ADM694 and ADM695) after V
reset threshold. This allows time for the power supply and mi-
croprocessor to stabilize. On power-down, the RESET output
remains low with V
microprocessor is held in a stable shutdown condition.
This RESET active time is adjustable on the ADM691/ADM693/
ADM695 by using an external oscillator or by connecting an
external capacitor to the OSC IN pin. Refer to Table I and
Figure 4.
The guaranteed minimum and maximum thresholds of the
ADM690/ADM691/ADM694/ADM695 are 4.5 V and 4.73 V,
while the guaranteed thresholds of the ADM692/ADM693 are
4.25 V and 4.48 V. The ADM690/ADM691/ADM694/ADM695
is, therefore, compatible with 5 V supplies with a +10%, –5%
tolerance while the ADM692/ADM693 is compatible with 5 V
mately 50 mV of hysteresis. The response time of the reset volt-
age comparator is less than 1 s. If glitches are present on the
V
should be decoupled close to the device.
In addition to RESET the ADM691/ADM693/ADM695 con-
tain an active high RESET output. This is the complement of
RESET and is intended for processors requiring an active high
RESET signal.
LOW LINE
CC
CC
10% supplies. The reset threshold comparator has approxi-
RESET
falls below the reset threshold, the RESET output is forced
line which could cause spurious reset pulses, then V
V
CC
t
V1 = RESET VOLTAGE THRESHOLD LOW
V2 = RESET VOLTAGE THRESHOLD HIGH
HYSTERESIS = V2–V1
1
= RESET TIME.
Figure 2. Power Fail Reset Timing
V2
t
CC
1
as low as 1 V. This ensures that the
V1
CC
CC
rises above the appropriate
is at an invalid level. When
V2
t
1
CC
V1
–6–
Watchdog Timer RESET
The watchdog timer circuit monitors the activity of the micro-
processor in order to check that it is not stalled in an indefinite
loop. An output line on the processor is used to toggle the
Watchdog Input (WDI) line. If this line is not toggled within the
selected timeout period, a RESET pulse is generated. The
nominal watchdog timeout period is preset at 1.6 seconds on the
ADM690/ADM692/ADM694. The ADM691/ADM693/ADM695
may be configured for either a fixed “short” 100 ms or a “long”
1.6 second timeout period or for an adjustable timeout period.
If the “short” period is selected, some systems may be unable to
service the watchdog timer immediately after a reset, so the
ADM691/ADM693/ADM695 automatically selects the “long”
timeout period directly after a reset is issued. The watchdog
timer is restarted at the end of reset, whether the reset was
caused by lack of activity on WDI or by V
reset threshold.
The normal (short) timeout period becomes effective following
the first transition of WDI after RESET has gone inactive. The
watchdog timeout period restarts with each transition on the
WDI pin. To ensure that the watchdog timer does not time out,
either a high-to-low or low-to-high transition on the WDI pin
must occur at or less than the minimum timeout period. If WDI
remains permanently either high or low, reset pulses will be
issued after each “long” timeout period (1.6 s). The watchdog
monitor can be deactivated by floating the Watchdog Input
(WDI) or by connecting it to midsupply.
RESET
WDO
Figure 3. Watchdog Timeout Period and Reset Active
Time
WDI
t
t
t
1
2
3
= WATCHDOG TIMEOUT PERIOD IMMEDIATELY FOLLOWING A RESET.
= RESET TIME.
= NORMAL (SHORT) WATCHDOG TIMEOUT PERIOD.
t
1
t
2
t
1
t
3
CC
falling below the
t
1
REV. A