AD ADM708AN Low cost up supervisory circuit Datasheet

a
FEATURES
Guaranteed RESET Valid with VCC = 1 V
190 ␮A Quiescent Current
Precision Supply-Voltage Monitor
4.65 V (ADM705/ADM707)
4.40 V (ADM706/ADM708)
200 ms Reset Pulsewidth
Debounced TTL/CMOS Manual Reset Input (MR)
Independent Watchdog Timer—1.6 sec Timeout
(ADM705/ADM706)
Active High Reset Output (ADM707/ADM708)
Voltage Monitor for Power-Fail or Low Battery
Warning
Superior Upgrade for MAX705–MAX708
Also Available in MicroSOIC Packages
Low Cost ␮P
Supervisory Circuits
ADM705–ADM708
FUNCTIONAL BLOCK DIAGRAMS
WATCHDOG
INPUT (WDI)
WATCHDOG
TRANSITION
DETECTOR
VCC
WATCHDOG
TIMER
RESET &
WATCHDOG
TIMEBASE
250␮A
MR
RESET
GENERATOR
GENERAL DESCRIPTION
The ADM705–ADM708 are low cost µP supervisory circuits.
They are suitable for monitoring the 5 V power supply/battery
and can also monitor microprocessor activity.
The ADM705/ADM706 provide the following functions:
1. Power-On Reset output during power-up, power-down and
brownout conditions. The RESET output remains operational with VCC as low as 1 V.
2. Independent watchdog timeout, WDO, that goes low if the
watchdog input has not been toggled within 1.6 seconds.
3. A 1.25 V threshold detector for power-fail warning, low
battery detection or to monitor a power supply other than
5 V.
4. An active low debounced manual reset input (MR).
RESET
VCC
4.65V*
ADM705/
ADM706
POWER-FAIL
INPUT (PFI)
1.25V
APPLICATIONS
Microprocessor Systems
Computers
Controllers
Intelligent Instruments
Critical ␮P Monitoring
Automotive Systems
Critical ␮P Power Monitoring
WATCHDOG
OUTPUT (WDO)
POWER-FAIL
OUTPUT (PFO)
*VOLTAGE REFERENCE = 4.65V (ADM705), 4.40V (ADM706)
VCC
250␮A
MR
RESET
RESET
GENERATOR
RESET
VCC
4.65V*
POWER-FAIL
INPUT (PFI)
1.25V
ADM707/
ADM708
POWER-FAIL
OUTPUT (PFO)
*VOLTAGE REFERENCE = 4.65V (ADM707), 4.40V (ADM708)
Two supply-voltage monitor levels are available. The ADM705/
ADM707 generate a reset when the supply voltage falls below
4.65 V, while the ADM706/ADM708 require that the supply
fall below 4.40 V before a reset is issued.
All parts are available in 8-lead DIP and SOIC packages. The
ADM707 and ADM708 are also available in space-saving
microSOIC packages.
The ADM707/ADM708 differ in that:
1. A watchdog timer function is not available.
2. An active high reset output in addition to the active low
output is available.
REV. B
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: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2000
ADM705–ADM708–SPECIFICATIONS (V
Parameter
Min
VCC Operating Voltage Range
Supply Current
1.0
Reset Threshold
4.5
4.25
Reset Threshold Hysteresis
Reset Pulsewidth
RESET Output Voltage
160
VCC – 1.5
CC
Typ
Max
Unit
190
5.5
250
V
µA
4.75
4.50
V
V
mV
ms
V
V
V
V
V
V
4.65
4.40
40
200
280
0.4
0.3
0.3
RESET Output Voltage
VCC – 1.5
0.4
Watchdog Timeout Period (tWD)
WDI Pulsewidth (tWP)
WDI Input Threshold
Logic Low
Logic High
WDI Input Current
WDO Output Voltage
1.00
50
1.60
2.25
0.8
3.5
–150
VCC – 1.5
50
–50
150
0.4
MR Pull-Up Current
MR Pulsewidth
MR Input Threshold
100
150
250
600
0.8
2.0
MR to Reset Output Delay
PFI Input Threshold
PFI Input Current
PFO Output Voltage
250
1.2
–25
VCC – 1.5
= 4.75 V to 5.5 V, TA = TMIN to TMAX unless otherwise noted.)
1.25
0.01
1.3
25
0.4
Test Conditions/Comments
ADM705, ADM707
ADM706, ADM708
ISOURCE = 800 µA
ISINK = 3.2 mA
VCC = 1 V, ISINK = 50 µA
VCC = 1.2 V, ISINK = 100 µA
ADM707, ADM708, ISOURCE = 800 µA
ADM707, ADM708, ISINK = 1.2 mA
sec
ns
VIL = 0.4 V, VIH = VCC × 0.8
V
V
µA
µA
V
V
WDI = VCC
WDI = 0 V
ISOURCE = 800 µA
ISINK = 1.2 mA
µA
ns
V
V
ns
V
nA
V
V
MR = 0 V
ISOURCE = 800 µA
ISINK = 3.2 mA
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS*
ORDERING GUIDE
(TA = 25°C unless otherwise noted)
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +6 V
All Other Inputs . . . . . . . . . . . . . . . . . . –0.3 V to VCC + 0.3 V
Input Current
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 mA
GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 mA
Digital Output Current . . . . . . . . . . . . . . . . . . . . . . . . . 20 mA
Power Dissipation, N-8 DIP . . . . . . . . . . . . . . . . . . . . 727 mW
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 135°C/W
Power Dissipation, SO-8 SOIC . . . . . . . . . . . . . . . . . . 470 mW
θJA 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >5 kV
Model
Temperature Range
Package Option
ADM705AN
ADM705AR
ADM706AN
ADM706AR
ADM707AN
ADM707AR
ADM707ARM
ADM708AN
ADM708AR
ADM708ARM
–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
N-8
SO-8
N-8
SO-8
N-8
SO-8
RM-8
N-8
SO-8
RM-8
*Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; 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
–2–
REV. B
ADM705–ADM708
PIN FUNCTION DESCRIPTION
Pin No.
Mnemonic
ADM705
ADM706
DIP, SOIC
ADM707
ADM708
DIP, SPOC MicroSOIC
MR
1
1
3
Manual Reset Input. When taken below 0.8 V, a RESET is generated. MR can be driven from TTL, CMOS logic or from a manual
reset switch as it is internally debounced. An internal 250 µA pull-up
current holds the input high when floating.
VCC
2
2
4
5 V Power Supply Input.
GND
3
3
5
0 V. Ground reference for all signals.
PFI
4
4
6
Power-Fail Input. PFI is the noninverting input to the Power-Fail
Comparator. When PFI is less than 1.25 V, PFO goes low. If unused,
PFI should be connected to GND or VCC.
PFO
5
5
7
Power-Fail Output. PFO is the output from the Power-Fail Comparator. It goes low when PFI is less than 1.25 V.
WDI
6
N/A
N/A
Watchdog Input. WDI is a three-level input. If WDI remains either
high or low for longer than the watchdog timeout period, the watchdog output WDO goes low. The timer resets with each transition at
the WDI input.
Function
Either a high-to-low or a low-to-high transition will clear the counter.
The internal timer is also cleared whenever reset is asserted. The
watchdog timer is disabled when WDI is left floating or connected to
a three-state buffer.
NC
N/A
6
8
No Connect.
RESET
7
7
1
Logic Output. RESET goes low for 200 ms when triggered. It can be
triggered either by VCC being below the reset threshold or by a low
signal on the manual reset (MR) input. RESET will remain low
whenever VCC is below the reset threshold (4.65 V in ADM705, 4.4 V
in ADM706). It remains low for 200 ms after VCC goes above the
reset threshold or MR goes from low to high. A watchdog timeout
will not trigger RESET unless WDO is connected to MR.
WDO
8
N/A
N/A
Logic Output. The Watchdog Output, WDO, goes low if the internal
watchdog timer times out as a result of inactivity on the WDI input. It
remains low until the watchdog timer is cleared. WDO also goes low
during low line conditions. Whenever VCC is below the reset threshold,
WDO remains low. As soon as VCC goes above the reset threshold,
WDO goes high immediately.
RESET
N/A
8
2
Logic Output. RESET is an active high output suitable for systems
that use active high RESET logic. It is the inverse of RESET.
DIP, SOIC
MR 1
PIN CONFIGURATION
DIP, SOIC
8 WDO
MR 1
VCC 2
ADM705/
ADM706
7 RESET
VCC 2
ADM707/
ADM708
7 RESET
GND 3
TOP VIEW
(Not to Scale)
6 WDI
GND 3
TOP VIEW
(Not to Scale)
6 NC
PFI 4
5 PFO
8 RESET
5 PFO
PFI 4
MicroSOIC
RESET 1
8 NC
RESET 2 ADM707/ 7 PFO
MR 3
VCC 4
ADM708
TOP VIEW
(Not to Scale)
6 PFI
5 GND
NC = NO CONNECT
NC = NO CONNECT
REV. B
–3–
ADM705–ADM708
Manual Reset (ADM707/ADM708)
WATCHDOG
INPUT (WDI)
WATCHDOG
TRANSITION
DETECTOR
VCC
WATCHDOG
TIMER
The manual reset input (MR) allows other reset sources, such as
a manual reset switch, to generate a processor reset. The input
is effectively debounced by the timeout period (200 ms typical).
The MR input is TTL/CMOS compatible, so it may also be
driven by any logic reset output.
WATCHDOG
OUTPUT (WDO)
RESET &
WATCHDOG
TIMEBASE
250␮A
MR
RESET
GENERATOR
RESET
VCC
VRT
VRT
VCC
tRS
4.65V*
ADM705/
ADM706
POWER-FAIL
INPUT (PFI)
1.25V
tRS
RESET
POWER-FAIL
OUTPUT (PFO)
MR EXTERNALLY
DRIVEN LOW
MR
*VOLTAGE REFERENCE = 4.65V (ADM705), 4.40V (ADM706)
Figure 1. ADM705/ADM706 Functional Block Diagram
WDO
VCC
Figure 3. RESET, MR, and WDO Timing
250␮A
MR
RESET
RESET
GENERATOR
Watchdog Timer (ADM705/ADM706)
The watchdog timer circuit may be used to monitor 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 timeout period (1.6 sec), the watchdog output
(WDO) goes low. The WDO output may be connected to a
nonmaskable interrupt (NMI) on the processor; therefore, if the
watchdog timer times out, an interrupt is generated. The interrupt service routine should then be used to rectify the problem.
RESET
VCC
4.65V*
POWER-FAIL
INPUT (PFI)
1.25V
ADM707/
ADM708
POWER-FAIL
OUTPUT (PFO)
*VOLTAGE REFERENCE = 4.65V (ADM707), 4.40V (ADM708)
Figure 2. ADM707/ADM708 Functional Block Diagram
If a RESET signal is required when a timeout occurs, the WDO
output should be connected to the manual reset input (MR).
CIRCUIT INFORMATION
Power-Fail RESET Output
RESET is an active low output that provides a RESET signal to
the Microprocessor whenever the VCC input is below the reset
threshold. An internal timer holds RESET low for 200 ms after
the voltage on VCC rises above the threshold. This is intended as
a power-on RESET signal for the microprocessor. It allows time
for both the power supply and the microprocessor to stabilize
after power-up. The RESET output is guaranteed to remain
valid (low) with VCC as low as 1 V. This ensures that the microprocessor is held in a stable shutdown condition as the power
supply voltage ramps up.
In addition to RESET, an active high RESET output is also
available on the ADM707/ADM708. This is the complement of
RESET and is useful for processors requiring an active high
RESET signal.
The watchdog timer is cleared by either a high-to-low or by a
low-to-high transition on WDI. It is also cleared by RESET
going low; therefore, the watchdog timeout period begins after
RESET goes high.
When VCC falls below the reset threshold, WDO is forced low
whether or not the watchdog timer has timed out. Normally,
this would generate an interrupt, but it is overridden by RESET
going low.
The watchdog monitor can be deactivated by floating the
Watchdog Input (WDI). The WDO output can now be used as
a low-line output since it will only go low when VCC falls below
the reset threshold.
tWP
tWD
tWD
tWD
WDI
WDO
RESET
RESET EXTERNALLY
TRIGGERED BY MR
tRS
Figure 4. Watchdog Timing
–4–
REV. B
ADM705–ADM708
Power-Fail Comparator
 R2 + R 3 
VH = 1.25 1 + 
 R1]
 R2 × R 3 
The power-fail comparator is an independent comparator that
may be used to monitor the input power supply. The comparator’s
inverting input is internally connected to a 1.25 V reference
voltage. The noninverting input is available at the PFI input.
This input may be used to monitor the input power supply via
a resistive divider network. When the voltage on the PFI input
drops below 1.25 V, the comparator output (PFO) goes low,
indicating a power failure. For early warning of power failure,
the comparator may be used to monitor the preregulator input
simply by choosing an appropriate resistive divider network.
The PFO output can be used to interrupt the processor so that
a shutdown procedure is implemented before the power is lost.
[
 1.25 VCC – 1.25 
–
VL = 1.25 + R1 

 R2

RE
 R1 + R2 
VMID = 1.25 

 R2 
Valid RESET Below 1 V VCC
The ADM70x family of products is guaranteed to provide a
valid reset level with VCC as low as 1 V; please refer to the Typical Performance Characteristics. As VCC drops below 1 V, the
internal transistor will not have sufficient drive to hold it ON so
the voltage on RESET will no longer be held at 0 V. A pull-down
resistor as shown in Figure 7 may be connected externally to
hold the line low if it is required.
INPUT
POWER
R1
PFO
1.25V
POWER-FAIL PFI
INPUT
R2
POWER-FAIL
OUTPUT
ADM70x
ADM70x
Figure 5. Power-Fail Comparator
RESET
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 6. When PFO is low, resistor R3 sinks current from the
summing junction at the PFI pin. When PFO is high, resistor
R3 sources current into the PFI summing junction. This results
in differing trip levels for the comparator. Further noise immunity may be achieved by connecting a capacitor between PFI
and GND.
7V TO 15V
INPUT POWER
GND
Figure 7. RESET Valid Below 1 V
5V
ADM663
VCC
R1
PFO
1.25V
TO ␮P NMI
PFI
R2
ADM70x
R3
5V
PFO
0V
0V
VH
VL
VIN
Figure 6. Adding Hysteresis to the Power-Fail Comparator
REV. B
R1
–5–
ADM705–ADM708–Typical Performance Characteristics
VCC = 5V
TA = 25ⴗC
A!
VCC
4.50V
1.3V
PFI
100
90
1.2V
4.4V
10
RESET
PFO
0%
1V
1V
500msHo
0V
500ns/DIV
Figure 8. RESET Output Voltage vs. Supply Voltage
A1
Figure 11. PFI Comparator Deassertion Response Time
VCC = VRT
TA = 25ⴗC
4.50V
5V
RESET
VCC
5V
100
90
RESET
RESET
10
0%
1V
1V
0V
500msHo
0V
100ns/DIV
Figure 12. RESET, RESET Assertion
Figure 9. ADM707/ADM708 RESET Output Voltage vs.
Supply Voltage
VCC = 5V
TA = 25ⴗC
VCC = VRT
TA = 25ⴗC
5V
RESET
1.3V
PFI
5V
RESET
1.2V
5V
PFO
0V
0V
0V
100ns/DIV
500ns/DIV
Figure 13. RESET, RESET Deassertion
Figure 10. PFI Comparator Assertion Response Time
–6–
REV. B
ADM705–ADM708
If, in the event of inactivity on the WDI line, a system reset is
required, then the WDO output should be connected to the MR
input as shown in Figure 16.
TA = 25ⴗC
5V
VCC
4V
5V
RESET
RESET
ADM705/
ADM706
␮P
I/O LINE
WDI
RESET
MR
WDO
GND
Figure 16. RESET from WDO
0V
Monitoring Additional Supply Levels
2␮s/DIV
It is possible to use the power-fail comparator to monitor a
second supply as shown in Figure 17. The two sensing resistors,
R1 and R2, are selected so that the voltage on PFI drops below
1.25 V at the minimum acceptable input supply. The PFO
output may be connected to the MR input so that a RESET is
generated when the supply drops out of tolerance. In this case, if
either supply drops out of tolerance, a RESET will be generated.
Figure 14. ADM705/ADM707 RESET Response Time
APPLICATIONS
A Typical Operating Circuit is shown in Figure 15. The unregulated dc input supply is monitored using the PFI input via the
resistive divider network. Resistors R1 and R2 should be selected
so that when the supply voltage drops below the desired level
(e.g., 8 V), the voltage on PFI drops below the 1.25 V threshold
thereby generating an interrupt to the µP. Monitoring the preregulator input gives additional time to execute an orderly
shutdown procedure before power is lost.
5V
VX
VCC
RESET
RESET
ADM705/
ADM706
R1
␮P
PFI
ADM666
IN
GND
OUT
MR
R2
5V
PFO
GND
UNREGULATED
DC
Figure 17. Monitoring 5 V and an Additional Supply, VX
VCC
RESET
WDI
R1
WDO
GND
PFO
VCC
␮Ps With Bidirectional RESET
I/O LINE
ADM705/
ADM706
PFI
MR
R2
RESET
In order to prevent contention for microprocessors with a bidirectional reset line, a current limiting resistor should be inserted
between the ADM70x RESET output pin and the µP reset pin.
This will limit the current to a safe level if there are conflicting
output reset levels. A suitable resistor value is 4.7 kΩ. If the
reset output is required for other uses, it should be buffered as
shown in Figure 18.
␮P
NMI
INTERRUPT
MANUAL
RESET
Figure 15. Typical Application Circuit
5V
Microprocessor activity is monitored using the WDI input. This
is driven using an output line from the processor. The software
routines should toggle this line at least once every 1.6 seconds.
If a problem occurs and this line is not toggled, WDO goes low
and a nonmaskable interrupt is generated. This interrupt routine may be used to clear the problem.
BUFFERED
RESET
VCC
ADM70x
RESET
GND
␮P
RESET
GND
Figure 18. Bidirectional I-O RESET
REV. B
–7–
ADM705–ADM708
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead Plastic DIP
(N-8)
8
C00088a–0–8/00 (rev. B)
0.39 (9.91)
MAX
5
0.25 0.31
(6.35) (7.87)
1
4
0.30 (7.62)
REF
0.035 ± 0.01
(0.89 ± 0.25)
PIN 1
0.165 ± 0.01
(4.19 ± 0.25)
0.18 ± 0.03
(4.57 ± 0.76)
0.125 (3.18)
MIN
0.018 ± 0.003
(0.46 ± 0.08)
0.033
(0.84)
NOM
0.10 (2.54)
TYP
SEATING
PLANE
0° - 15°
0.011 ± 0.003
(4.57 ± 0.76)
8-Lead SOIC
(SO-8)
0.1968 (5.00)
0.1890 (4.80)
8
5
0.1574 (4.00)
0.1497 (3.80) 1
PIN 1
0.0098 (0.25)
0.0040 (0.10)
4
0.2440 (6.20)
0.2284 (5.80)
0.0688 (1.75)
0.0532 (1.35)
0.0196 (0.50)
x 45°
0.0099 (0.25)
0.0500 0.0192 (0.49)
SEATING (1.27)
0.0098 (0.25)
PLANE BSC 0.0138 (0.35) 0.0075 (0.19)
8°
0° 0.0500 (1.27)
0.0160 (0.41)
8-Lead MicroSOIC
(RM-8)
0.122 (3.10)
0.114 (2.90)
1
5
0.199 (5.05)
0.187 (4.75)
4
PRINTED IN U.S.A.
8
0.122 (3.10)
0.114 (2.90)
PIN 1
0.0256 (0.65) BSC
0.120 (3.05)
0.112 (2.84)
0.006 (0.15)
0.002 (0.05)
0.120 (3.05)
0.112 (2.84)
0.043 (1.09)
0.027 (0.68)
0.018 (0.46)
SEATING
0.008 (0.20)
PLANE
0.011 (0.28)
0.003 (0.08)
–8–
33°
27°
0.027 (0.68)
0.015 (0.38)
REV. B