a
Microprocessor
Supervisory Circuits
ADM690A/ADM692A/ADM802L/M/ADM805L/M
FUNCTIONAL BLOCK DIAGRAM
V
BATT
BATTERY
SWITCHOVER
V
CC
V
OUT
FEATURES
Precision Supply Voltage Monitor
4.65 V ADM690A/ADM802L/ADM805L
4.40 V ADM692A/ADM802M/ADM805M
Reset Assertion Down to 1 V V
CC
Reset Timeout—200 ms
Watchdog Timer—1.6 s
100 A Quiescent Supply Current
Automatic Battery Backup Power Switching
Voltage Monitor for Power Fail
2% Power Fail Accuracy on ADM802L/M
Space-Saving MicroSOIC Package (ADM690A)
APPLICATIONS
Microprocessor Systems
Computers
Controllers
Intelligent Instruments
4.65V*
RESET
GENERATOR
RESET
(RESET)
WATCHDOG
INPUT (WDI)
WATCHDOG
TRANSITION DETECTOR
(1.6s)
POWER FAIL
INPUT (PFI)
1.25V
ADM690A
ADM692A
ADM802L
ADM802M
ADM805L
ADM805M
POWER FAIL
OUTPUT (PFO)
*4.4V FOR ADM692A/ADM802M/ADM805M
( ) = ADM805L/M ONLY
GENERAL DESCRIPTION
The ADM690A/ADM692A/ADM802L/M/ADM805L/M
family of supervisory circuits offers complete single chip
solutions for power supply monitoring and battery control
functions in microprocessor systems. These functions include
µP
reset, backup battery switchover, watchdog timer, and power
failure warning.
The ADM690A/ADM692A/ADM802L/M/ADM805L/M are
available in 8-pin packages and provide:
1. Power-on reset output during power-up, power-down and
brownout conditions. The
RESET
output remains opera-
tional with V
CC
as low as 1 V.
2. Battery backup switching for CMOS RAM, CMOS
microprocessor or other low power devices.
3. A reset pulse if the optional watchdog timer has not been
toggled within 1.6 seconds.
4. A 1.25 V threshold detector for power fail warning, low battery
detection, or to monitor a power supply other than +5 V.
On the ADM690A/ADM802L/ADM805L the reset voltage
threshold is 4.65 V. On the ADM692A/ADM802M/
ADM805M, the reset voltage threshold is 4.40 V.
The ADM802L/ADM802M guarantee power fail accuracies to
±
2%.
The ADM805L/M provides an active high reset output, RESET
instead of
RESET.
The family of products is fabricated using an advanced epitaxial
CMOS process combining low power consumption and high
reliability.
RESET
assertion is guaranteed with V
CC
as low as 1 V.
They provide a pin-compatible upgrade for the MAX690A/
MAX692A/MAX802L/MAX802M/MAX805L
All parts are available in 8-pin DIP and SOIC packages. The
ADM690A is also available in a new space-saving microSOIC
package.
REV. 0
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 or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
World Wide Web Site: http://www.analog.com
Fax: 617/326-8703
© Analog Devices, Inc., 1996
ADM690A/ADM692A/ADM802L/M/ADM805L/M–SPECIFICATIONS
(V
CC
= 4.75 V to 5.5 V (ADM690A/ADM802L/ADM805L), V
CC
= 4.5 V to 5.5 V, (ADM692A/ADM802M/ADM805M), V
BATT
= +2.8 V, T
A
= T
MIN
to T
MAX
unless otherwise noted)
Parameter
Min
Typ
Max
5.5
100
1.0
+0.02
V
CC
– 0.01
V
CC
– 0.05
V
CC
– 0.02
V
BATT
– 0.002
20
–20
40
Units
V
µA
µA
µA
V
V
V
V
mV
mV
mV
Test Conditions/Comments
V
CC
/V
BATT
OPERATION
1
V
CC
Operating Voltage Range
1.0
Supply Current (Excludes I
OUT
)
Supply Current in Battery Backup Mode
Battery Standby Current
(+ = Discharge, – = Charge)
–0.1
V
OUT
Output Voltage
V
CC
– 0.02
V
CC
– 0.5
V
OUT
in Battery Backup Mode
Battery Switchover Threshold
Battery Switchover Hysteresis
RESET THRESHOLD
Reset Voltage Threshold
ADM690A, ADM802L, ADM805L
ADM692A, ADM802M, ADM805M
ADM802L
ADM802M
Reset Threshold Hysteresis
Reset Timeout Delay
RESET
Output Voltage
V
BATT
– 0.05
70
0.05
V
CC
= 0 V, V
BATT
= 2.8 V
5.5 V > V
CC
> V
BATT
+ 0.2 V
I
OUT
= 5 mA
I
OUT
= 50 mA
I
OUT
= 250 mA
I
OUT
= 250
µA,
V
CC
< V
BATT
– 0.2 V
Power Up
Power Down
4.5
4.25
4.55
4.30
140
V
CC
– 1.5
0.8
V
CC
– 1.5
4.65
4.4
4.75
4.5
4.7
4.45
280
0.4
0.3
40
200
RESET Output Voltage
0.4
WATCHDOG TIMER
Watchdog Timeout Period
WDI Input Pulse Width
WDI Input Threshold
Logic Low
Logic High
WDI Input Current
POWER FAIL DETECTOR
PFI Input Threshold
PFI Input Current
PFO
Output Voltage
NOTES
1
Either V
CC
or V
BATT
can be 0 V if the other > +2.0 V.
Specifications subject to change without notice.
V
V
V
V
mV
ms
V
V
V
V
V
V
s
ns
V
V
µA
µA
V
V
nA
V
V
T
A
= 25°C, V
CC
Falling
T
A
= 25°C, V
CC
Falling
I
SOURCE
= 800
µA
I
SINK
= 3.2 mA
I
SINK
= 100
µA,
V
CC
= 1 V
I
SOURCE
= 4
µA,
V
CC
= 1.1 V
ADM805L/M, I
SOURCE
= 800
µA
ADM805L/M, I
SINK
= 3.2 mA
1.0
50
1.6
2.25
V
IL
= 0.4, V
IH
= 0.8 (V
CC
)
0.8
3.5
10
–10
1.20
1.225
–25
V
CC
– 1.5
1.25
1.25
0.01
1.30
1.275
+25
0.4
WDI = V
CC
WDI = 0 V
ADM690A, ADM692A, ADM805L/M
ADM802L/M
I
SOURCE
= 800
µA
I
SINK
= 3.2 mA
–2–
REV. 0
ADM690A/ADM692A/ADM802L/M/ADM805L/M
ABSOLUTE MAXIMUM RATINGS*
(T
A
= +25°C unless otherwise noted)
ORDERING GUIDE
V
CC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +6 V
V
BATT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +6 V
All Other Inputs . . . . . . . . . . . . . . . . . . –0.3 V to V
CC
+ 0.3 V
Input Current
V
CC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .200 mA
V
BATT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 mA
GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 mA
Digital Output Current . . . . . . . . . . . . . . . . . . . . . . . . 20 mA
Power Dissipation, N-8 DIP . . . . . . . . . . . . . . . . . . . 400 mW
θ
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . . 120°C/W
Power Dissipation, SO-8 SOIC . . . . . . . . . . . . . . . . . 500 mW
θ
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . . 110°C/W
Operating Temperature Range
Industrial (A Version) . . . . . . . . . . . . . . . . –40°C to +85°C
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . +300°C
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . +215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . +220°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >4 kV
*Stresses above those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. This is a stress rating only and functional
operation of the device at these or any other conditions above those listed in the
operational sections of this specification is not implied. Exposure to absolute
maximum ratings for extended periods of time may affect device reliability.
Model
ADM690AAN
ADM690AARN
ADM690AARM
ADM692AAN
ADM692AARN
ADM802LAN
ADM802LARN
ADM802MAN
ADM802MARN
ADM805LAN
ADM805LARN
ADM805MAN
ADM805MARN
Temperature
Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
PIN CONFIGURATIONS
V
OUT
1
V
CC
2
GND 3
PFI 4
ADM690A
ADM692A
ADM802L
ADM802M
ADM805L
ADM805M
TOP VIEW
(Not to Scale)
Package
Option
N-8
SO-8
RM-8
N-8
SO-8
N-8
SO-8
N-8
SO-8
N-8
SO-8
N-8
SO-8
8 V
BATT
7 RESET (RESET)
6 WDI
5 PFO
PIN FUNCTION DESCRIPTION
Mnemonic
V
CC
V
BATT
V
OUT
GND
PFI
PFO
RESET
Function
Power Supply Input: +5 V Nominal.
Backup Battery Input. As V
CC
falls below the reset threshold and below V
BATT
by 20 mV, V
BATT
will be switched
to V
OUT
. On power-up as V
CC
rises to 20 mV above V
BATT
, V
OUT
will be switched back to V
CC
.
Output Voltage. When V
CC
is above the reset threshold, V
OUT
is connected to V
CC
through an on chip switch.
When V
CC
is below the reset threshold, the higher of V
CC
or V
BATT
is connected to V
OUT
.
0 V. Ground reference for all signals.
Power Fail Comparator Input. If PFI is less than 1.25 V, the power fail output
PFO
goes low. If unused, PFI
should be connected to V
CC
or GND.
Power Fail Comparator Output. If PFI is less than 1.25 V, the power fail output
PFO
goes low.
Logic Output.
RESET
goes low if
1. V
CC
falls below the Reset Threshold
2. The watchdog timer is not serviced within its timeout period (1.6 seconds)
The reset threshold is typically 4.65 V for the ADM690A/ADM802L/ADM805L and 4.4 V for the ADM692A/
ADM802M/ADM805M.
RESET
remains low for 200 ms after V
CC
returns above the threshold.
RESET
also
goes low for 200 ms if the watchdog timer is enabled but not serviced within its timeout period.
Active high RESET output (ADM805L/M only). This is the inverse of
RESET.
The asserted (high) level is V
CC
or V
BATT
whichever is higher.
Watchdog Input. WDI is a three level input. If WDI remains either high or low for longer than 1.6 s, (RESET)
(RESET) is activated. The timer resets with each transition on the WDI line. The watchdog timer may be
disabled if WDI is left floating or is connected to a high impedance three stated logic output.
RESET
WDI
REV. 0
–3–
ADM690A/ADM692A/ADM802L/M/ADM805L/M
Typical Performance Curves
3
5.00
4.98
2.75
R
OUT
= 9.3Ω
4.96
4.88
R
OUT
= 0.53Ω
V
OUT
– V
2.5
V
OUT
– V
4.92
4.9
2.25
4.88
4.86
2
10
20
30
40
I
OUT
– mA
50
60
70
4.84
20
50
100
I
OUT
– mA
150
200
Figure 1. Output Voltage vs. Load Current in Battery
Backup
Figure 4. Output Voltage vs. Load Current in Normal
Operation
T
A
= +25 C
5V
100
90
100
90
PFO
PFO
1.3V
PFI
1.2V
10
0%
10
0%
0V
1.2V
200mV
2µs
1.3V
PFI
200mV
2µs
Figure 2. Power Fail Comparator Response Time L
¨
H
Figure 5. Power Fail Comparator Response Time H
¨
L
T
A
= +25 C
5V
V
CC
100
90
100
4V
90
RESET
10
0%
10
0%
1V
10µs
1V
400ms
Figure 3. ADM690A
RESET
Response Time
Figure 6.
RESET
Output Voltage vs. V
CC
–4–
REV. 0
ADM690A/ADM692A/ADM802L/M/ADM805L/M
V
BATT
BATTERY
SWITCHOVER
V
CC
+5V
V
CC
V
OUT
0V
V
OUT
4.65V*
RESET
GENERATOR
RESET
(RESET)
0V
+5V
RESET
3.0V
t
RS
WATCHDOG
INPUT (WDI)
WATCHDOG
TRANSITION DETECTOR
(1.6s)
POWER FAIL
INPUT (PFI)
1.25V
ADM690A
ADM692A
ADM802L
ADM802M
ADM805L
ADM805M
POWER FAIL
OUTPUT (PFO)
0V
+5V
RESET
3.0V
0V
+5V
PFO
0V
V
BATT
= PFI = 3.0V
*4.4V FOR ADM692A/ADM802M/ADM805M
( ) = ADM805L/M ONLY
Figure 7. Functional Block Diagram
POWER FAIL
RESET,
RESET
Figure 8. Timing Diagram
BATTERY SWITCHOVER SECTION
RESET
is an active low output which provides a
RESET
signal
to the microprocessor whenever V
CC
is at an invalid level. When
V
CC
falls below the reset threshold, the
RESET
output is forced
low. The nominal reset voltage threshold is 4.65 V (ADM690A/
ADM802L/ADM805L or 4.4 V ADM692A/ADM802M/
ADM805M.
On power-up
RESET
will remain low for 200 ms after V
CC
rises
above the reset threshold. This allows time for the power supply
and microprocessor to stabilize. On power-down, the
RESET
output remains low with V
CC
as low as 1 V. This ensures that
the microprocessor is held in a stable shutdown condition.
The guaranteed minimum and maximum thresholds are as follows:
ADM690A/ADM802L/ADM805L: 4.5 V and 4.75 V
ADM692A: 4.25 V and 4.5 V.
ADM802L: 4.55 V and 4.7 V
ADM802M: 4.3 V and 4.45 V
The ADM805L and ADM805M contain an active high reset
output. This is the complement of
RESET
and is intended for
processors requiring an active high RESET signal.
The guaranteed minimum and maximum thresholds for the
ADM805 are:
ADM805L: 4.5 V and 4.75 V
ADM805M: 4.25 V and 4.5 V.
Watchdog Timer
RESET,
RESET
During normal operation with V
CC
higher than the reset
threshold, V
CC
is internally switched to V
OUT
via an internal
PMOS transistor switch. This switch has a typical on-resistance
of less than 1
Ω
and can supply up to 100 mA at the V
OUT
terminal. Once V
CC
falls below the reset threshold, the higher of
V
CC
or V
BATT
is switched to V
OUT
. This means that V
BATT
connects to V
OUT
only when V
CC
is below the reset threshold
and V
BATT
is greater than V
CC
.
V
OUT
is normally used to drive a RAM memory bank which
may require instantaneous currents of greater than 100 mA. If
this is the case, then a bypass capacitor should be connected to
V
OUT
. The capacitor will provide the peak current transients to the
RAM. A capacitance value of 0.1
µF
or greater may be used.
A 9
Ω
MOSFET switch connects the V
BATT
input to V
OUT
during battery backup. This MOSFET has very low input-to-
output differential (dropout voltage) at the low current levels
required for battery backup of CMOS RAM or other low power
CMOS circuitry. The supply current in battery backup is
typically 0.05
µA.
Typically 3 V batteries are used as the backup supply. High
value capacitors, either standard electrolytic or the farad size
double layer capacitors, can also be used for short-term memory
back up. A small charging current of typically 10 nA (0.1
µA
max) flows out of the V
BATT
terminal. This current is useful for
maintaining rechargeable batteries in a fully charged condition.
This extends the life of the back up battery by compensating for
its self discharge current. Also note that this current poses no
problem when lithium batteries are used for back up since the
maximum charging current (0.1
µA)
is safe for even the smallest
lithium cells.
If the battery-switchover section is not used, V
BATT
should be
connected to GND and V
OUT
should be connected to V
CC
.
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
1.6 seconds, a RESET pulse is generated. 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 timeout period (1.6 s). The watchdog monitor
can be deactivated by floating the Watchdog Input (WDI) or by
connecting it to midsupply.
REV. 0
–5–
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