Datasheet ADM695, ADM694, ADM693, ADM691, ADM692 Datasheet (Analog Devices)

...
Microprocessor
4.65V
1
WATCHDOG
TRANSITION DETECTOR
1.3V
ADM691 ADM693 ADM695
V
OUT
V
BATT
V
CC
WATCHDOG
INPUT (WDI)
POWER FAIL
INPUT (PFI)
1
VOLTAGE DETECTOR = 4.65V (ADM691, ADM695)
4.40V (ADM693)
POWER FAIL OUTPUT (PFO)
RESET
WATCHDOG
TIMER
RESET &
WATCHDOG
TIMEBASE
RESET
GENERATOR
BATT ON
OSC IN
OSC SEL
WATCHDOG OUTPUT (WDO)
RESET
LOW LINE
CE
OUT
CE
IN
4.65V
1
RESET
GENERATOR
2
WATCHDOG
TRANSITION DETECTOR
(1.6s)
1.3V
ADM690 ADM692 ADM694
V
OUT
V
BATT
V
CC
WATCHDOG
INPUT (WDI)
POWER FAIL
INPUT (PFI)
1
VOLTAGE DETECTOR = 4.65V (ADM690, ADM694)
4.40V (ADM692)
2
RESET PULSE WIDTH = 50ms (ADM690, ADM692)
200ms (ADM694)
POWER FAIL OUTPUT (PFO)
RESET
a
FEATURES Superior Upgrade for MAX690–MAX695 Specified Over Temperature Low Power Consumption (5 mW) Precision Voltage Monitor Reset Assertion Down to 1 V V Low Switch On-Resistance 1.5 V Normal,
20 V in Backup High Current Drive (100 mA) Watchdog Timer—100 ms, 1.6 s, or Adjustable 600 nA Standby Current Automatic Battery Backup Power Switching Extremely Fast Gating of Chip Enable Signals (5 ns) Voltage Monitor for Power Fail
APPLICATIONS Microprocessor Systems Computers Controllers Intelligent Instruments Automotive Systems
CC
ADM690–ADM695
FUNCTIONAL BLOCK DIAGRAMS
GENERAL DESCRIPTION
The ADM690–ADM695 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, CMOS RAM write protection, and power failure warn­ing. The complete family provides a variety of configurations to satisfy most microprocessor system requirements.
The ADM690, ADM692 and ADM694 are available in 8-pin DIP packages and provide:
1. Power-on reset output during power-up, power-down and brownout conditions. The tional with V
as low as 1 V.
CC
RESET output remains opera-
2. Battery backup switching for CMOS RAM, CMOS microprocessor or other low power logic.
3. A reset pulse if the optional watchdog timer has not been toggled within a specified time.
4. A 1.3 V threshold detector for power fail warning, low battery detection, or to monitor a power supply other than +5 V.
The ADM691, ADM693 and ADM695 are available in 16-pin DIP and small outline packages and provide three additional functions.
1. Write protection of CMOS RAM or EEPROM.
2. Adjustable reset and watchdog timeout periods.
3. Separate watchdog timeout, backup battery switchover, and low V
REV. A
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.
status outputs.
CC
The ADM690–ADM695 family is fabricated using an advanced epitaxial CMOS process combining low power consumption (5 mW), extremely fast Chip Enable gating (5 ns) and high reli­ability.
RESET assertion is guaranteed with VCC as low as 1 V. In addition, the power switching circuitry is designed for mini­mal voltage drop thereby permitting increased output current drive of up to 100 mA without the need for an external pass transistor.
© Analog Devices, Inc., 1996
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
ADM690–ADM695–SPECIFICA TIONS
(VCC = Full Operating Range, V T
unless otherwise noted)
MAX
= +2.8 V, TA = T
BATT
Parameter Min Typ Max Units Test Conditions/Comments
BATTERY BACKUP SWITCHING
V
Operating Voltage Range
CC
ADM690, ADM691, ADM694, ADM695 4.75 5.5 V ADM692, ADM693 4.5 5.5 V
V
Operating Voltage Range
BATT
ADM690, ADM691, ADM694, ADM695 2.0 4.25 V ADM692, ADM693 2.0 4.0 V
V
Output Voltage VCC – 0.05 VCC – 0.025 V I
OUT
V
in Battery Backup Mode V
OUT
Supply Current (Excludes I
) 1 1.95 mA I
OUT
V
– 0.5 VCC – 0.25 V I
CC BATT
– 0.05 V
– 0.02 V I
BATT
Supply Current in Battery Backup Mode 0.6 1 µAV Battery Standby Current 5.5 V > V
(+ = Discharge, – = Charge) –0.1 +0.02 µAT
= 1 mA
OUT
100 mA
OUT
= 250 µA, VCC < V
OUT
= 100 mA
OUT
= 0 V, V
CC
= +25°C
A
CC
BATT
> V
= 2.8 V
+ 0.2 V
BATT
BATT
– 0.2 V
–1.0 +0.02 µA Battery Switchover Threshold 70 mV Power Up V
CC
– V
BATT
50 mV Power Down Battery Switchover Hysteresis 20 mV BATT ON Output Voltage 0.3 V I BATT ON Output Short Circuit Current 35 mA BATT ON = V
= 3.2 mA
SINK
= 4.5 V Sink Current
OUT
0.5 1 25 µA BATT ON = 0 V Source Current
RESET AND WATCHDOG TIMER
Reset Voltage Threshold
ADM690, ADM691, ADM694, ADM695 4.5 4.65 4.73 V
ADM692, ADM693 4.25 4.4 4.48 V Reset Threshold Hysteresis 40 mV Reset Timeout Delay
ADM690, ADM691, ADM692, ADM693 35 50 70 ms OSC SEL = HIGH, V
ADM694, ADM695 140 200 280 ms OSC SEL = HIGH, V Watchdog Timeout Period, Internal Oscillator 1.0 1.6 2.25 s Long Period, V
70 100 140 ms Short Period, V
CC CC
= 5 V, TA = +25°C
CC
= 5 V, TA = +25°C
CC
= 5 V, TA = +25°C
= 5 V, TA = +25°C
Watchdog Timeout Period, External Clock 3840 4097 Cycles Long Period
768 1025 Cycles Short Period
Minimum WDI Input Pulse Width 50 ns V
RESET Output Voltage @ VCC = +1 V 4 200 mV I RESET, LOW LINE Output Voltage 0.4 V I
3.5 V I
RESET, WDO Output Voltage 0.4 V I
3.5 V I
= 0.4, VIH = 3.5 V
IL
= 10 µA, VCC = 1 V
SINK
= 1.6 mA, VCC = 4.25 V
SINK
= 1 µA, VCC = 5 V
SOURCE
= 1.6 mA, VCC = 5 V
SINK
= 1 µA, VCC = 4.25 V
SOURCE
Output Short Circuit Source Current 1 3 25 µA Output Short Circuit Sink Current 25 mA WDI Input Threshold V
CC
= 5 V
1
Logic Low 0.8 V
Logic High 3.5 V WDI Input Current 20 50 µA WDI = V
, TA = +25°C
OUT
–50 –15 µA WDI = 0 V, TA = +25°C
POWER FAIL DETECTOR
PFI Input Threshold 1.25 1.3 1.35 V V
= +5 V
CC
PFI Input Current –25 ±0.01 +25 nA PFO Output Voltage 0.4 V I
3.5 V I
= 3.2 mA
SINK SOURCE
= 1 µA
PFO Short Circuit Source Current 1 3 25 µA PFI = Low, PFO = 0 V PFO Short Circuit Sink Current 25 mA PFI = High, PFO = V
OUT
CHIP ENABLE GATING
CE
Threshold 0.8 V V
IN
3.0 V V
CE
Pull-Up Current 3 µA
IN
CE
Output Voltage 0.4 V I
OUT
V
– 1.5 V I
OUT
V
– 0.05 V I
OUT
IL IH
= 3.2 mA
SINK
= 3.0 mA
SOURCE
= 1 µA, VCC = 0 V
SOURCE
CE Propagation Delay 5 9 ns
MIN
to
–2–
REV. A
ADM690–ADM695
Parameter Min Typ Max Units Test Conditions/Comments
OSCILLATOR
OSC IN Input Current ±2 µA OSC SEL Input Pull-Up Current 5 µA OSC IN Frequency Range 0 250 kHz OSC SEL = 0 V OSC IN Frequency with External Capacitor 4 kHz OSC SEL = 0 V, C
NOTE
1
WDI is a three level input which is internally biased to 38% of VCC and has an input impedance of approximately 125 k.
Specifications subject to change without notice.
= 47 pF
OSC
ABSOLUTE MAXIMUM RATINGS*
(TA = +25°C unless otherwise noted)
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +6 V
V
All Other Inputs . . . . . . . . . . . . . . . . . . –0.3 V to V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +6 V
BATT
OUT
+ 0.5 V
Input Current
V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 mA
CC
V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 mA
BATT
GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 mA
Digital Output Current . . . . . . . . . . . . . . . . . . . . . . . . . 20 mA
Power Dissipation, N-8 DIP . . . . . . . . . . . . . . . . . . . .400 mW
θ
Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 120°C/W
JA
Power Dissipation, Q-8 DIP . . . . . . . . . . . . . . . . . . . .500 mW
θ
Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 125°C/W
JA
Power Dissipation, N-16 DIP . . . . . . . . . . . . . . . . . . .600 mW
θ
Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 135°C/W
JA
Power Dissipation, Q-16 DIP . . . . . . . . . . . . . . . . . . . 600 mW
θ
Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 100°C/W
JA
Power Dissipation, R-16 SOIC . . . . . . . . . . . . . . . . . .600 mW
θ
Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 110°C/W
JA
Operating Temperature Range
Industrial (A Version) . . . . . . . . . . . . . . . . . –40°C to +85°C
Extended (S Version) . . . . . . . . . . . . . . . . .–55°C to +125°C
Lead Temperature (Soldering, 10 secs) . . . . . . . . . . . . +300°C
Vapor Phase (60 secs) . . . . . . . . . . . . . . . . . . . . . . . +215°C
Infrared (15 secs) . . . . . . . . . . . . . . . . . . . . . . . . . . . +220°C
Storage Temperature Range . . . . . . . . . . . . . –65°C to +150°C
ORDERING GUIDE
Model Temperature Range Package Option
ADM690AN –40°C to +85°C N-8 ADM690AQ –40°C to +85°C Q-8 ADM690SQ –55°C to +125°C Q-8
ADM691AN –40°C to +85°C N-16 ADM691AR –40°C to +85°C R-16 ADM691AQ –40°C to +85°C Q-16 ADM691SQ –55°C to +125°C Q-16
ADM692AN –40°C to +85°C N-8 ADM692AQ –40°C to +85°C Q-8 ADM692SQ –55°C to +125°C Q-8
ADM693AN –40°C to +85°C N-16 ADM693AR –40°C to +85°C R-16 ADM693AQ –40°C to +85°C Q-16 ADM693SQ –55°C to +125°C Q-16
ADM694AN –40°C to +85°C N-8 ADM694AQ –40°C to +85°C Q-8 ADM694SQ –55°C to +125°C Q-8
ADM695AN –40°C to +85°C N-16 ADM695AR –40°C to +85°C R-16 ADM695AQ –40°C to +85°C Q-16 ADM695SQ –55°C to +125°C Q-16
*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.
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the ADM690–ADM695 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
REV. A
–3–
WARNING!
ESD SENSITIVE DEVICE
ADM690–ADM695
Mnemonic Function
PIN FUNCTION DESCRIPTION
V V V
CC BATT OUT
Power Supply Input: +5 V Nominal. Backup Battery Input. Connect to Ground if a backup battery is not used. Output Voltage, VCC or V
can supply up to 100 mA to power CMOS RAM. Connect V
is internally switched to V
BATT
depending on which is at the highest potential. V
OUT
to VCC if V
OUT
OUT
and V
are not used.
BATT
OUT
GND 0 V. Ground reference for all signals. RESET Logic Output. RESET goes low if
1. V
falls below the Reset Threshold
CC
2. V
falls below V
CC
BATT
3. The watchdog timer is not serviced within its timeout period. The reset threshold is typically 4.65 V for the ADM690/ADM691/ADM694/ADM695 and 4.4 V for the ADM692 and
ADM693. after V serviced within its timeout period. The shown in Table I. The
RESET remains low for 50 ms (ADM690/ADM691/ADM692/ADM693) or 200 ms (ADM694/ADM695)
returns above the threshold. RESET also goes low for 50 (200) ms if the watchdog timer is enabled but not
CC
RESET pulse width can be adjusted on the ADM691/ADM693/ADM695 as
RESET output has an internal 3 µA pull up, and can either connect to an open collector
Reset bus or directly drive a CMOS gate without an external pull-up resistor.
WDI Watchdog Input. WDI is a three level input. If WDI remains either high or low for longer than the watchdog timeout
period,
RESET pulses low and WDO goes low. The timer resets with each transition on the WDI line. The watchdog
timer may be disabled if WDI is left floating or is driven to midsupply.
PFI Power Fail Input. PFI is the noninverting input to the Power Fail Comparator when PFI is less than 1.3 V,
goes low. Connect PFI to GND or V
when not used.
OUT
PFO
PFO Power Fail Output. PFO is the output of the Power Fail Comparator. It goes low when PFI is less than 1.3 V. The
comparator is turned off and
CE
CE
IN OUT
Logic Input. The input to the CE gating circuit. Connect to GND or V Logic Output. CE
threshold. If V
OUT
is below the reset threshold, CE
CC
BATT ON Logic Output. BATT ON goes high when V
PFO goes low when VCC is below V
is a gated version of the CEIN signal. CE
is forced high. See Figures 5 and 6.
OUT
is internally switched to the V
OUT
.
BATT
if not used.
OUT
tracks CEIN when VCC is above the reset
OUT
input. It goes low when V
BATT
OUT
is internally switched to VCC. The output typically sinks 35 mA and can directly drive the base of an external PNP transistor to increase the output current above the 100 mA rating of V
OUT
.
LOW LINE Logic Output. LOW LINE goes low when VCC falls below the reset threshold. It returns high as soon as VCC rises
above the reset threshold.
RESET Logic Output. RESET is an active high output. It is the inverse of
RESET.
OSC SEL Logic Oscillator Select Input. When OSC SEL is unconnected (floating) or driven high, the internal oscillator sets
the reset active time and watchdog timeout period. When OSC SEL is low, the external oscillator input, OSC IN, is enabled. OSC SEL has a 3 µA internal pull up, (see Table I).
OSC IN Oscillator Logic Input. With OSC SEL low, OSC IN can be driven by an external clock signal or an external
capacitor can be connected between OSC IN and GND. This sets both the reset active pulse timing and the watch­dog timeout period (see Table I and Figure 4). With OSC SEL high or floating, the internal oscillator is enabled and the reset active time is fixed at 50 ms typ. (ADM691/ADM693) or 200 ms typ (ADM695). In this mode the OSC IN pin selects between fast (100 ms) and slow (1.6 s) watchdog timeout periods. In both modes, the timeout period immediately after a reset is 1.6 s typical.
WDO Logic Output. The Watchdog Output, WDO, goes low if WDI remains either high or low for longer than the
watchdog timeout period.
WDO is set high by the next transition at WDI. If WDI is unconnected or at midsupply,
the watchdog timer is disabled and WDO remains high. WDO also goes high when LOW LINE goes low.
–4–
REV. A
PIN CONFIGURATIONS
ADM690–ADM695
V
BATT
V
OUT
V
GND
BATT ON LOW LINE
OSC IN
OSC SEL
CC
1
2
3 4
5
(Not to Scale)
6
7
8
ADM691 ADM693 ADM695
TOP VIEW
16
15 14
13
12
11
10
9
RESET
RESET
WDO
CE
IN
CE
OUT
WDI
PFO
PFI
V
OUT
V
GND
PFI
CC
1
2
3
(Not to Scale)
4
ADM690 ADM692 ADM694
TOP VIEW
8
7
6 5
V
BATT
RESET WDI PFO
PRODUCT SELECTION GUIDE
Part Nominal Reset Nominal V
CC
Nominal Watchdog Battery Backup Base Drive Chip Enable
Number Time Reset Threshold Timeout Period Switching Ext PNP Signals
ADM690 50 ms 4.65 V 1.6 s Yes No No ADM691 50 ms or ADJ 4.65 V 100 ms, 1.6 s, ADJ Yes Yes Yes ADM692 50 ms 4.4 V 1.6 s Yes No No ADM693 50 ms or ADJ 4.4 V 100 ms, 1.6 s, ADJ Yes Yes Yes ADM694 200 ms 4.65 V 1.6 s Yes No No ADM695 200 ms or ADJ 4.65 V 100 ms, 1.6 s, ADJ Yes Yes Yes
CIRCUIT INFORMATION Battery Switchover Section
The battery switchover circuit compares VCC to the V input, and connects V occurs when V when V
CC
is 50 mV higher than V
CC
is 70 mV greater than V
to whichever is higher. Switchover
OUT
BATT
as VCC falls, and
BATT
as VCC rises. This
20 mV of hysteresis prevents repeated rapid switching if V
BATT
CC
falls very slowly or remains nearly equal to the battery voltage.
If the continuous output current requirement at V 100 mA or if a lower V
CC–VOUT
voltage differential is desired,
OUT
exceeds
an external PNP pass transistor may be connected in parallel with the internal transistor. The BATT ON output (ADM691/ ADM693/ADM695) can directly drive the base of the external transistor.
A 20 MOSFET switch connects the V
input to V
BATT
OUT
during battery backup. This MOSFET has very low input-to­output differential (dropout voltage) at the low current levels required for battery back up of CMOS RAM or other low power CMOS circuitry. The supply current in battery back up is typically 0.6 µA.
The ADM690/ADM691/ADM694/ADM695 operates with battery voltages from 2.0 V to 4.25 V and the ADM692/ADM693 operates with battery voltages from 2.0 V to 4.0 V. 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
terminal. This current is useful for
BATT
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
Figure 1. Battery Switchover Schematic
During normal operation with VCC higher than V ternally switched to V
via an internal PMOS transistor
OUT
, VCC is in-
BATT
switch. This switch has a typical on-resistance of 1.5 and can supply up to 100 mA at the V
terminal. V
OUT
is normally
OUT
smallest lithium cells. If the battery-switchover section is not used, V
connected to GND and V
should be connected to VCC.
OUT
should be
BATT
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
. The capacitor
OUT
will provide the peak current transients to the RAM. A capaci­tance value of 0.1 µF or greater may be used.
REV. A
–5–
ADM690–ADM695
POWER FAIL RESET OUTPUT
RESET is an active low output which provides a RESET signal to the Microprocessor whenever V V
falls below the reset threshold, the RESET output is forced
CC
is at an invalid level. When
CC
low. The nominal reset voltage threshold is 4.65 V (ADM690/ ADM691/ADM694/ADM695) or 4.4 V (ADM692/ADM693).
V
RESET
LOW LINE
CC
V2 V2
t
1
t
= RESET TIME.
1
V1 = RESET VOLTAGE THRESHOLD LOW V2 = RESET VOLTAGE THRESHOLD HIGH HYSTERESIS = V2–V1
V1 V1
t
1
Figure 2. Power Fail Reset Timing
On power-up RESET will remain low for 50 ms (200 ms for ADM694 and ADM695) after V
rises above the appropriate
CC
reset threshold. This allows time for the power supply and mi­croprocessor to stabilize. On power-down, the remains low with V
as low as 1 V. This ensures that the
CC
RESET output
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 ± 10% supplies. The reset threshold comparator has approxi­mately 50 mV of hysteresis. The response time of the reset volt­age comparator is less than 1 µs. If glitches are present on the V
line which could cause spurious reset pulses, then V
CC
CC
should be decoupled close to the device. In addition to
tain an active high
RESET the ADM691/ADM693/ADM695 con-
RESET output. This is the complement of
RESET and is intended for processors requiring an active high
RESET signal.
Watchdog Timer RESET
The watchdog timer circuit monitors the activity of the micro­processor 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
falling below the
CC
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.
WDI
WDO
t
2
RESET
t
1
t
= RESET TIME.
1
t
= NORMAL (SHORT) WATCHDOG TIMEOUT PERIOD.
2
t
= WATCHDOG TIMEOUT PERIOD IMMEDIATELY FOLLOWING A RESET.
3
t
1
t
3
t
1
Figure 3. Watchdog Timeout Period and Reset Active Time
–6–
REV. A
ADM690–ADM695
OSC IN
OSC SEL
ADM691 ADM693 ADM695
8
7
C
OSC
Table I. ADM691, ADM693, ADM695 Reset Pulse Width and Watchdog Timeout Selections
Watchdog Timeout Period Reset Active Period
Immediately
OSC SEL OSC IN Normal After Reset ADM691/ADM693 ADM695
Low External Clock Input 1024 CLKS 4096 CLKS 512 CLKS 2048 CLKS Low External Capacitor 260 ms × C/47 pF 1.04 s × C/47 pF 130 ms × C/47 pF 520 ms × C/47 pF Floating or High Low 100 ms 1.6 s 50 ms 200 ms Floating or High Floating or High 1.6 s 1.6 s 50 ms 200 ms
NOTE With the OSC SEL pin low, OSC IN can be driven by an external clock signal, or an external capacitor can be connected between OSC IN and GND. The nominal internal oscillator frequency is 10.24 kHz. The nominal oscillator frequency with external capacitor is: F
The watchdog timeout period is fixed at 1.6 seconds, and the reset pulse width is fixed at 50 ms on the ADM690/ADM692. On the ADM694 the watchdog timeout period is also 1.6 sec­onds but the reset pulse width is fixed at 200 ms. The ADM691/ ADM693/ADM695 allow these times to be adjusted as shown in Table I. Figure 4 shows the various oscillator configurations which can be used to adjust the reset pulse width and watchdog timeout period.
The internal oscillator is enabled when OSC SEL is high or floating. In this mode, OSC IN selects between the 1.6 second and 100 ms watchdog timeout periods. With OSC IN connected high or floating, the 1.6 second timeout period is selected; while with it connected low, the 100 ms timeout period is selected. In either case, immediately after a reset, the timeout period is 1.6 seconds. This gives the microprocessor time to reinitialize the system. If OSC IN is low, then the 100 ms watchdog period be­comes effective after the first transition of WDI. The software should be written such that the I/O port driving WDI is left in its power-up reset state until the initialization routines are com­pleted and the microprocessor is able to toggle WDI at the mini­mum watchdog timeout period of 70 ms.
Watchdog Output (WDO)
The Watchdog Output WDO (ADM691/ADM693/ADM695)
Figure 4c. Internal Oscillator (1.6 Second Watchdog)
provides a status output which goes low if the watchdog timer “times out” and remains low until set high by the next transition on the Watchdog Input.
WDO is also set high when VCC goes
below the reset threshold.
8
OSC SEL
ADM691 ADM693
CLOCK
0 TO 250kHz
7
OSC IN
ADM695
(Hz) = 184,000/C (pF).
OSC
Figure 4b. External Capacitor
NC
NC
NC
8
7
8
7
OSC SEL
ADM691 ADM693 ADM695
OSC IN
OSC SEL
ADM691 ADM693 ADM695
OSC IN
REV. A
Figure 4d. Internal Oscillator (100 ms Watchdog)
Figure 4a. External Clock Source
–7–
ADM690–ADM695
ADM69x
POWER
FAIL
INPUT
R
2
INPUT
POWER
1.3V
PFO
POWER FAIL OUTPUT
R
1
CE Gating and RAM Write Protection (ADM691/ADM693/ ADM695)
The ADM691/ADM693/ADM695 products include memory protection circuitry which ensures the integrity of data in mem­ory by preventing write operations when V level. There are two additional pins,
CE
is at an invalid
CC
and CE
IN
OUT
, which may be used to control the Chip Enable or Write inputs of CMOS RAM. When V of
CE
, with a 5 ns propagation delay. When VCC falls below
IN
the reset voltage threshold or V
CE
high, independent of CEIN.
OUT
CE
typically drives the CE, CS, or write input of battery
OUT
is present, CE
CC
BATT
is a buffered replica
OUT
, an internal gate forces
backed up CMOS RAM. This ensures the integrity of the data in memory by preventing write operations when V
is at an in-
CC
valid level. Similar protection of EEPROMs can be achieved by using the
If the 5 ns typical propagation delay of nect
CE
to drive the store or write inputs.
OUT
CE
to GND and use the resulting CE
IN
CE
is excessive, con-
OUT
to control a
OUT
high speed external logic gate.
ADM69x
CE
IN
LOW = 0
V
CC
V
OK = 1
CC
CE
OUT
Power Fail Warning Comparator
An additional comparator is provided for early warning of failure in the microprocessor’s power supply. The Power Fail Input (PFI) is compared to an internal +1.3 V reference. The Power Fail Output (
PFO) goes low when the voltage at PFI is less than
1.3 V. Typically PFI is driven by an external voltage divider which senses either the unregulated dc input to the system’s 5 V regulator or the regulated 5 V output. The voltage divider ratio can be chosen such that the voltage at PFI falls below 1.3 V sev­eral milliseconds before the +5 V power supply falls below the reset threshold.
PFO is normally used to interrupt the micropro­cessor so that data can be stored in RAM and the shut down procedure executed before power is lost
Figure 7. Power Fail Comparator
Table II. Input and Output Status In Battery Backup Mode
Figure 5. Chip Enable Gating
V
CC
V2 V2
V1 V1
Signal Status
V
OUT
V
OUT
PMOS switch.
is connected to V
via an internal
BATT
RESET Logic low.
RESET
t
1
t
1
RESET Logic high. The open circuit output voltage is
equal to V
OUT
.
LOW LINE Logic low.
LOW LINE
BATT ON Logic high. The open circuit voltage is equal to
V
OUT.
WDI WDI is ignored. It is internally disconnected
from the internal pull-up resistor and does not
CE
IN
source or sink current as long as its input voltage
is between GND and V
. The input voltage
OUT
does not affect supply current. WDO Logic high. The open circuit voltage is equal
CE
OUT
t
= RESET TIME.
1
V1 = RESET VOLTAGE THRESHOLD LOW V2 = RESET VOLTAGE THRESHOLD HIGH HYSTERESIS = V2–V1
Figure 6. Chip Enable Timing
to V PFI The Power Fail Comparator is turned off and
has no effect on the Power Fail Output.
PFO Logic low.
CE
IN
CE
from its internal pull-up and does not source or
sink current as long as its input voltage is
between GND and V
.
OUT
is ignored. It is internally disconnected
IN
. The input voltage
OUT
does not affect supply current.
CE
OUT
OSC IN OSC IN is ignored. OSC SEL OSC SEL is ignored.
–8–
Logic high. The open circuit voltage is equal to
V
.
OUT
REV. A
T ypical Performance Curves–ADM690–ADM695
10
90
100
0%
3.36 V
500ms
A4
1V1V
4.70
4.62 20 120
4.68
4.64
40
4.66
1008060
TEMPERATURE – °C
RESET VOLTAGE THRESHOLD – V
VCC = +5V
POWER-UP
POWER-DOWN
ADM690 ADM691 ADM694 ADM695
6
0
1.8
1.25
0
1.35
2
0
1
3
4
5
1.61.0 1.20.6 0.8 1.40.40.2
VCC = 5V T
A
= +25°C
V
PFI
1.3V
30pF
PFO
+5V
10k
+5V
TIME – µs
5.00 VCC = 5V
TA = +25°C
4.95
– V
4.90
OUT
V
4.85
4.80 0 100
Figure 8. V
SLOPE = 1.5
20
OUT
I
– mA
OUT
vs. I
OUT
Operation
1.303
1.302
1.301
1.300
PFI INPUT THRESHOLD – V
806040
Normal
2.80
VCC = 0V V
BATT
T
I
OUT
vs. I
µA
= +25°C
A
OUT
2.79
– V
2.78
OUT
V
2.77
2.76 0 1000
Figure 9. V
SLOPE = 20
200
OUT
Backup
53
52
51
50
RESET ACTIVE TIME – ms
= +2.8V
800600400
Battery
VCC = +5V
ADM690 ADM691 ADM692 ADM693
Figure 10. Reset Output Voltage vs. Supply Voltage
1.299 20 120
Figure 11. PFI Input Threshold vs. Temperature
6 5 4 3 2 1 0
1.35
1.25
0
Figure 14. Power Fail Comparator Response Time
REV. A
40
TEMPERATURE – °C
V
PFI
1.3V
TIME – µs
PFO
1008060
VCC = 5V T
= +25°C
A
30pF
49
20 120
40
TEMPERATURE – °C
Figure 12. Reset Active Time vs. Temperature
6
VCC = 5V
5
T
= +25°C
A
4 3 2 1 0
1.35
1.25
0.80.5 0.60.3 0.4 0.70.20.1
0
V
PFI
1.3V
TIME – µs
Figure 15. Power Fail Comparator Response Time
PFO
1008060
30pF
Figure 13. Reset Voltage Threshold vs. Temperature
90
8050 6030 40 702010
Figure 16. Power Fail Comparator Response Time with Pull-Up Resistor
–9–
ADM690–ADM695
+APPLICATION INFORMATION Increasing the Drive Current
If the continuous output current requirements at V 100 mA or if a lower V
CC–VOUT
voltage differential is desired,
OUT
exceed
an external PNP pass transistor may be connected in parallel with the internal transistor. The BATT ON output (ADM691/ ADM693/ADM695) can directly drive the base of the external transistor.
+5V
INPUT
POWER
BATTERY
PNP TRANSISTOR
V
CC
V
BATT
ADM691 ADM693 ADM695
BATT
ON
0.1µF0.1µF
V
OUT
Figure 17. Increasing the Drive Current
Using a Rechargeable Battery for Back Up
If a capacitor or a rechargeable battery is used for back up then the charging resistor should be connected to V
since this
OUT
eliminates the discharge path that would exist during power down if the resistor is connected to V
+5V
INPUT
POWER
0.1µF
RECHARGEABLE
BATTERY
V
BATT
V
CC
CC
V
OUT
I =
R
ADM69x
.
– V
BATT
R
0.1µF
V
OUT
Figure 18. Rechargeable Battery
Adding Hysteresis to the Power Fail Comparator
For increased noise immunity, hysteresis may be added to the power fail comparator. Since the comparator circuit is nonin­verting, hysteresis can be added simply by connecting a resistor be­tween the
PFO output and the PFI input as shown in Figure 19.
PFO is low, resistor R3 sinks current from the summing
When junction at the PFI pin. When tion of R
and R4 source current into the PFI summing junc-
3
PFO is high, the series combina-
tion. This results in differing trip levels for the comparator.
+5V
+7V TO +15V
INPUT
POWER
7805
R
1
R
2
5V
PFO
0V
0V
VH = 1.3V (1+ ––– + –––
VL = 1.3V (1+ ––– – –––––––––––––
ASSUMING R HYSTERESIS V
PFI
ADM69x
V
L
R
R
1
R
R
2
R1 (5V – 1.3V)
R
1
1.3V (R
R
2
R3 THEN
< <
4
– VL = 5V (–––
H
1 3
1.3V
V
IN
)
3 + R4
V
CC
R
3
V
H
)
)
R
1
)
R
2
PFO
R
4
TO
µP NMI
Figure 19. Adding Hysteresis to the Power Fail Comparator
Monitoring the Status of the Battery
The power fail comparator can be used to monitor the status of the backup battery instead of the power supply if desired. This is shown in Figure 20. The PFI input samples the battery volt­age and generates an active low
PFO signal when the battery voltage drops below a chosen threshold. It may be necessary to apply a test load in order to determine the loaded battery volt­age. This can be done under processor control using Since CE
is forced high during the battery backup mode, the
OUT
CE
OUT.
test load will not be applied to the battery while it is in use, even if the microprocessor is not powered.
–10–
REV. A
BATTERY
OPTIONAL
TEST LOAD
20k
10M
10M
V
PFI
CE
BATT
OUT
+5V INPUT POWER
V
CC
ADM69x
PFO
LOW BATTERY
CE
IN
APPLIES TEST LOAD
SIGNAL TO
µP I/O PIN
FROM µP I/O PIN
TO BATTERY
CONTROL INPUT*
ADM690–ADM695
OSC SEL
D1
D2
OSC IN
*LOW = INTERNAL TIMEOUT HIGH = EXTERNAL TIMEOUT
ADM69x
Figure 20. Monitoring the Battery Status
Alternate Watchdog Input Drive Circuits
The watchdog feature can be enabled and disabled under pro­gram control by driving WDI with a 3-state buffer (Figure 21a). When three-stated, the WDI input will float thereby disabling the watchdog timer.
WATCHDOG STROBE
CONTROL INPUT
WDI
ADM69x
Figure 21a. Programming the Watchdog Input
This circuit is not entirely foolproof, and it is possible that a software fault could erroneously 3-state the buffer. This would then prevent the ADM69x from detecting that the microproces­sor is no longer operating correctly. In most cases a better method is to extend the watchdog period rather than disabling the watchdog. This may be done under program control using the circuit shown in Figure 21b. When the control input is high, the OSC SEL pin is low and the watchdog timeout is set by the external capacitor. A 0.01 µF capacitor sets a watchdog timeout delay of 100 seconds. When the control input is low, the OSC SEL pin is driven high, selecting the internal oscillator. The 100 ms or the 1.6 s period is chosen, depending on which diode in Figure 21b is used. With D1 inserted the internal timeout is set at 100 ms, while with D2 inserted the timeout is set at 1.6 s.
Figure 21b. Programming the Watchdog Input
Replacing the Backup Battery
When changing the backup battery with system power on, spuri­ous resets can occur when the battery is removed. This occurs because the leakage current flowing out of the V charge up the stray capacitance. If the voltage on V within 50 mV of V
, a reset pulse is generated.
CC
BATT
pin will
reaches
BATT
If spurious resets during battery replacement are acceptable, then no action is required. If not, then one of the following solutions should be considered:
1. A capacitor from V
to GND. This gives time while the
BATT
capacitor is charging up to replace the battery. The leakage current will charge up the external capacitor towards the V
CC
level. The time taken is related to the charging current, the size of external capacitor and the voltage differential between the capacitor and the charging voltage supply.
t = C
EXT
× V
DIFF
/I
The maximum leakage (charging) current is 1 µA over tem- perature and V
= VCC–V
DIFF
. Therefore, the capacitor
BATT
size should be chosen such that sufficient time is available to make the battery replacement.
C
EXT
= T
(1 µA/(VCC–V
REQD
BATT
))
If a replacement time of 5 seconds is allowed and assuming a V
of 4.5 V and a V
CC
BATTERY
BATT
C
EXT
C
EXT
of 3 V
= 3.33 µF
V
BATT
ADM69x
REV. A
Figure 22a. Preventing Spurious RESETS During Battery Replacement
2. A resistor from V on V
BATT
replacement.
–11–
to GND. This will prevent the voltage
BATT
from rising to within 50 mV of VCC during battery
ADM690–ADM695
ADM690 ADM692 ADM694
R
2
R
1
PFO
+5V
V
CC
CMOS RAM
POWER
I/O LINE
µP NMI
µP RESET
µP SYSTEM
µP POWER
V
OUT
RESET
WDI
GND
PFI
V
BATT
BATTERY
+
0.1µF
ADM690 ADM692 ADM694
R
2
R
1
PFO
7805
INPUT
POWER
V > 8V
+5V
V
CC
CMOS RAM
POWER
I/O LINE
µP NMI
µP RESET
µP SYSTEM
µP POWER
V
OUT
RESET
WDI
GND
PFI
V
BATT
0.1µF
BATTERY
0.1µF
R =(V
– 50 mV)/1 µA
CC
Note that the resistor will discharge the battery slightly. With a V
supply of 4.5 V, a suitable resistor is 4.3 M. With a 3 V
CC
battery this will draw around 700 nA. This will be negligible in most cases.
V
BATT
BATTERY
R
ADM69x
Figure 22b. Preventing Spurious RESETS During Battery Replacement
TYPICAL APPLICATIONS ADM690, ADM692 AND ADM694
Figure 23 shows the ADM690/ADM692/ADM694 in a typical power monitoring, battery backup application. V CMOS RAM. Under normal operating conditions with V present, V occurs, V
is internally connected to VCC. If a power failure
OUT
will decay and V
CC
will be switched to V
OUT
powers the
OUT
BATT
CC
thereby maintaining power for the CMOS RAM. A RESET pulse is also generated when V ADM690/ADM694 or 4.4 V for the ADM692. remain low for 50 ms (200 ms for ADM694) after V
falls below 4.65 V for the
CC
RESET will
CC
returns
to 5 V. The watchdog timer input (WDI) monitors an I/O line from the
µP system. This line must be toggled once every 1.6 seconds to verify correct software execution. Failure to toggle the line indi­cates that the µP system is not correctly executing its program and may be tied up in an endless loop. If this happens, a reset pulse is generated to initialize the processor.
If the watchdog timer is not needed, the WDI input should be left floating.
The Power Fail Input, PFI, monitors the input power supply via a resistive divider network. The voltage on the PFI input is com­pared with a precision 1.3 V internal reference. If the input volt­age drops below 1.3 V, a power fail output (
PFO) signal is generated. This warns of an impending power failure and may be used to interrupt the processor so that the system may be shut down in an orderly fashion. The resistors in the sensing network are ratioed to give the desired power fail threshold voltage V
.
T
= (1.3 R1/R2) + 1.3 V
V
T
= (VT/1.3) – 1
R
1/R2
Figure 23a. ADM690/ADM692/ADM694 Typical Application Circuit A
Figure 23b shows a similar application but in this case the PFI input monitors the unregulated input to the 7805 voltage regu­lator. This gives an earlier warning of an impending power fail­ure. It is useful with processors operating at low speeds or
where there are a significant number of housekeeping tasks to be completed before the power is lost.
Figure 23b. A DM690/ADM692/ADM694 Typical Application Circuit B
ADM691, ADM693, ADM695
A typical connection for the ADM691/ADM693/ADM695 is shown in Figure 24. CMOS RAM is powered from V 5 V power is present this is routed to V V
is routed to V
BATT
V
, but if more current is required, an external PNP transistor
CC
can be added. When V
. V
OUT
CC
can supply up to 100 mA from
OUT
is higher than V
. If VCC fails then
OUT
, the BATT ON
BATT
OUT
. When
output goes low, providing up to 25 mA of base drive for the external transistor. A 0.1 µF capacitor is connected to V supply the transient currents for CMOS RAM. When V lower than V backup battery to V
, an internal 20 MOSFET connects the
BATT
OUT
.
OUT
CC
to
is
–12–
REV. A
ADM690–ADM695
INPUT POWER +5V
0.1µF
RESET
CMOS
RAM
ADDRESS
DECODE
0.1µF
A0–A15
I/O LINE NMI RESET
µP
R
R
1
2
3V
BATTERY
NC
0.1µF
V
CC
V
BATT
PFI GND
OSC IN OSC SEL
LOW LINE WDO
SYSTEM STATUS
INDICATORS
BATT
ON
ADM691 ADM693 ADM695
V
OUT
CE
OUT
CE
WDI
PFO
RESET
IN
Figure 24. ADM691/ADM693/ADM695 Typical Application
Reset Output
The internal voltage detector monitors VCC and generates a RESET output to hold the microprocessor’s Reset line low when V timer holds after V repeated toggling of
is below 4.65 V (4.4 V for ADM693). An internal
CC
RESET low for 50 ms (200 ms for the ADM695)
rises above 4.65 V (4.4 V for ADM693). This prevents
CC
RESET even if the 5 V power drops out
and recovers with each power line cycle. The crystal oscillator normally used to generate the clock for mi-
croprocessors can take several milliseconds to stabilize. Since most microprocessors need several clock cycles to reset,
RESET
must be held low until the microprocessor clock oscillator has started. The power-up
RESET pulse lasts 50 ms (200 ms for the ADM695) to allow for this oscillator start-up time. If a different reset pulse width is required, then a capacitor should be con­nected to OSC IN or an external clock may be used. Please refer to Table I and Figure 4. The manual reset switch and the 0.1 µF capacitor connected to the reset line can be omitted if a manual reset is not needed. An inverted, active high, RESET output is also available.
Power Fail Detector
The +5 V V
power line is monitored via a resistive potential
CC
divider connected to the Power Fail Input (PFI). When the voltage at PFI falls below 1.3 V, the Power Fail Output (
PFO) drives the processor’s NMI input low. If for example a Power Fail threshold of 4.8 V is set with resistors R processor will have the time when V
CC
and R2, the micro-
1
falls from 4.8 V to 4.65 V to save data into RAM. An earlier power fail warning can be generated if the unregulated dc input to the 5 V regulator is available for monitoring. This will allow more time for micro­processor housekeeping tasks to be completed before power is lost.
RAM Write Protection
The ADM691/ADM693/ADM695 CE Select inputs of the CMOS RAM. as V
is above the 4.65 V (4.4 V for ADM693) reset threshold.
CC
falls below the reset threshold, CE
If V
CC
pendent of the logic level at
CE
CE
. This prevents the micropro-
IN
line drives the Chip
OUT
follows CEIN as long
OUT
goes high, inde-
OUT
cessor from writing erroneous data into RAM during power-up, power-down, brownouts and momentary power interruptions.
Watchdog Timer
The microprocessor drives the Watchdog Input (WDI) with an I/O line. When OSC IN and OSC SEL are unconnected, the microprocessor must toggle the WDI pin once every 1.6 sec­onds to verify proper software execution. If a hardware or soft­ware failure occurs such that WDI not toggled, the ADM691/ ADM693 will issue a 50 ms (200 ms for ADM695)
RESET
pulse after 1.6 seconds. This typically restarts the micro­processor’s power-up routine. A new
RESET pulse is issued every 1.6 seconds until WDI is again strobed. If a different watchdog timeout period is required, then a capacitor should be connected to OSC IN or an external clock may be used. Please refer to Table I and Figure 4.
The WATCHDOG OUTPUT ( dog timer is not serviced within its timeout period. Once
WDO) goes low if the watch-
WDO
goes low, it remains low until a transition occurs at WDI. The watchdog timer feature can be disabled by leaving WDI unconnected.
The
RESET output has an internal 3 µA pull-up, and can either connect to an open collector reset bus or directly drive a CMOS gate without an external pull-up resistor.
REV. A
–13–
ADM690–ADM695
PIN 1
0.210 (5.33)
MAX
0.160 (4.06)
0.115 (2.93)
0.022 (0.558)
0.014 (0.356)
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Pin Plastic DIP (N-8)
58
0.280 (7.11)
0.240 (6.10)
0.100 (2.54) BSC
4
0.070 (1.77)
0.045 (1.15)
0.060 (1.52)
0.015 (0.38)
0.150 (3.81) MIN
SEATING PLANE
0.325 (8.25)
0.300 (7.62)
0.015 (0.381)
0.008 (0.204)
1
0.430 (10.92)
0.348 (8.84)
16-Lead Plastic DIP (N-16)
0.195 (4.95)
0.115 (2.93)
PIN 1
0.210 (5.33)
0.200 (5.05)
0.125 (3.18)
16
1
0.022 (0.558)
0.014 (0.356)
SEATING
0.022 (0.558)
0.014 (0.356)
PIN 1
PLANE
0.200 (5.08)
MAX
0.840 (21.33)
0.745 (18.93)
0.100 (2.54)
BSC
0.070 (1.77)
0.045 (1.15)
8-Pin Cerdip (Q-8)
MAX
BSC
5
4
0.070 (1.78)
0.30 (0.76)
8
1
0.420 (10.67)
0.100 (2.54)
9
8
0.310 (7.87)
0.220 (5.59)
0.060 (1.52)
0.015 (0.38)
0.150 (3.81) MIN
0.280 (7.11)
0.240 (6.10)
0.060 (1.52)
0.015 (0.38)
0.150 (3.81)
SEATING PLANE
0.325 (8.25)
0.300 (7.62)
0.015 (0.381)
0.008 (0.204)
0.320 (8.13)
0.290 (7.37)
0.015 (0.381)
0.008 (0.204)
0.195 (4.95)
0.115 (2.93)
–14–
REV. A
16-Lead Cerdip (Q-16)
ADM690–ADM695
SEATING
PLANE
0.299
(7.60)
0.012 (0.3)
PIN 1
0.200 (5.08)
MAX
16
0.022 (0.558)
0.014 (0.356)
1
0.05 (1.27)
1
0.840 (21.34) MAX
0.100 (2.54) BSC
16-Lead SOIC (R-16)
916
8
0.413 (10.50)
0.019 (0.49)
REF
0.070 (1.78)
0.30 (0.76)
0.419
(10.65)
0.104 (2.65)
9
8
0.030
(0.75)
0.013 (0.32)
0.310 (7.87)
0.220 (5.59)
0.060 (1.52)
0.015 (0.38)
0.150 (3.81) MIN
0.320 (8.13)
0.290 (7.37)
0.015 (0.381)
0.008 (0.204)
0.042 (1.07)
REV. A
–15–
C1782a–2–6/96
–16–
PRINTED IN U.S.A.
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