ADM690A Datasheet PDF - Analog Devices
| Part Number | ADM690A | |
| Description | Microprocessor Supervisory Circuits | |
| Manufacturers | Analog Devices | |
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a
Microprocessor
Supervisory Circuits
ADM690A/ADM692A/ADM802L/M/ADM805L/M
FEATURES
Precision Supply Voltage Monitor
4.65 V ADM690A/ADM802L/ADM805L
4.40 V ADM692A/ADM802M/ADM805M
Reset Assertion Down to 1 V VCC
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
FUNCTIONAL BLOCK DIAGRAM
VBATT
VCC
BATTERY
SWITCHOVER
VOUT
4.65V*
RESET
GENERATOR
RESET
(RESET)
WATCHDOG
INPUT (WDI)
POWER FAIL
INPUT (PFI)
WATCHDOG
TRANSITION DETECTOR
(1.6s)
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 VCC 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 VCC 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
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ADM690A/ADM692A/ADM802L/M/ADM805L/M
VBATT
VCC
BATTERY
SWITCHOVER
VOUT
4.65V*
RESET
GENERATOR
RESET
(RESET)
WATCHDOG
INPUT (WDI)
POWER FAIL
INPUT (PFI)
WATCHDOG
TRANSITION DETECTOR
(1.6s)
1.25V
ADM690A
ADM692A
ADM802L
ADM802M
ADM805L
ADM805M
POWER FAIL
OUTPUT (PFO)
*4.4V FOR ADM692A/ADM802M/ADM805M
( ) = ADM805L/M ONLY
Figure 7. Functional Block Diagram
POWER FAIL RESET, RESET
RESET is an active low output which provides a RESET signal
to the microprocessor whenever VCC is at an invalid level. When
VCC 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 VCC 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 VCC 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
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.
+5V
VCC
0V
VOUT
3.0V
0V
+5V
RESET
0V
+5V
RESET
0V
3.0V
+5V
PFO
0V
tRS
VBATT = PFI = 3.0V
Figure 8. Timing Diagram
BATTERY SWITCHOVER SECTION
During normal operation with VCC higher than the reset
threshold, VCC is internally switched to VOUT 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 VOUT
terminal. Once VCC falls below the reset threshold, the higher of
VCC or VBATT is switched to VOUT. This means that VBATT
connects to VOUT only when VCC is below the reset threshold
and VBATT is greater than VCC.
VOUT 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
VOUT. 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 VBATT input to VOUT
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 VBATT 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, VBATT should be
connected to GND and VOUT should be connected to VCC.
REV. 0
–5–
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| Information | Total 8 Pages | |
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| Download | [ ADM690A.PDF Datasheet ] | |
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Featured Datasheets
| Part Number | Description | MFRS |
| ADM690 | The function is Microprocessor Supervisory Circuits. Analog Devices | |
| ADM690A | The function is Microprocessor Supervisory Circuits. Analog Devices | |
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