AS1916 - AS1918
Microprocessor Supervisory Circuits with Manual Reset and Watchdog
www.austriamicrosystems.com/Supervisors/AS1916 Revision 1.04 1 - 14
Datasheet
1 General Description
The AS1916 - AS1918 microprocessor supervisory circuits were
designed to generate a reset when the monitored supply voltage falls
below a factory-trimmed threshold. The reset remains asserted for a
minimum timeout period after the supply voltage stabilizes.
Guaranteed to be in the correct state for VCC higher than +1.0V,
these devices are ideal for portable and battery-powered systems
with strict monitoring requirements.
The devices feature factory-trimmed thresholds to monitor a supply
voltage between 1.8 and 3.6V.
The devices are available with the reset output types listed in Table
1.
The AS1916 - AS1918 include a manual-reset input for systems that
never fully power down the microprocessor.
Additionally, these devices feature a watchdog timer to help ensure
that the processor is operating within proper code boundaries.
The AS1916 - AS1918 are available in a 5-pin SOT23 package.
Figure 1. Typical Application Diagram
2 Key Features
VCC Supervisory Range: +1.8 to +3.6V
Guaranteed Reset Valid Down to VCC = +1.0V
Reset Timeout Delay: 215ms
Manual Reset Input
Three Reset Output Types
- Active-Low Push/Pull (AS1916)
- Active-High Push/Pull (AS1917)
- Active-Low Open-Drain (AS1918)
Watchdog Timeout Period: 1.5s
Immune to Fast Negative VCC Transients
External Components Not Required
Operating Temperature Range: -40 to +125°C
5-pin SOT23 Package
3 Applications
The devices are ideal for portable and battery-powered systems,
embedded controllers, intel lig ent instruments, automotive systems,
and critical CPU monitoring applications.
Table 1. Standard Products
Model Reset Output Type
AS1916 Active-Low Push/Pull
AS1917 Active-High Push/Pull
AS1918 Active-Low Open-Drain
AS1916/
AS1918
External
Reset
CPU
I/O Supply
VCC
GND
RESETN
I/O
4
WDI
5
VCC
3
MRN
GND 2
1
RESETN
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AS1916 - AS1918
Datasheet - Pin Assignments
4 Pin Assignments
Figure 2. Pin Assignments (Top View)
4.1 Pin Descriptions
Table 2. Pin Descriptions
Pin Number Pin Name Description
1
RESETN
Active-Low Reset Output (AS1916, AS1918). The RESETN signal toggles from high to low when VCC, or
MRN is pulled low, or the watchdog triggers a reset. This output signal remains low for the reset timeout period
after all supervised voltages exceed their reset threshold, or MRN goes low to high, or the watchdog triggers a
reset.
RESET
Active-High Reset Output (AS1917). The RESET signal toggles from low to high when VCC, or MRN is pulled
low, or the watchdog triggers a reset. This output signal remains high for the reset timeout period (see tRP on
page 4) after all supervised voltages exceed their reset threshold, or MRN goes low to high, or the watchdog
triggers a reset.
2GND
Ground
3MRN
Active-Low Manual Reset Input. Pulling this pin low asserts a reset. This pin is connected to the internal 50kΩ
pullup to VCC. This reset remains active as long as MRN is low and for the reset timeout period (see tRP on
page 4) after MRN goes high.
Note: If the manual reset feature is not used, this pin should be unconnected or connected to VCC.
4WDI
Wa tchdog Input. If WDI remains high or low for longer than the watchdog timeout period (see tWD on page 5),
the internal watchdog timer period expires and a reset is triggered for the reset timeout period (see tRP on page
4). The internal watchdog timer clears whenever a reset is a asserted or when WDI senses a rising or falling
edge.
Note: To disable the watchdog feature, this pin must be unconnected or connected to a tri-state buffer output.
WDI must be low or unconnected (tristate) during the reset timeout period tRP, (see Figure 11 on page 8).
5VCC
Supervised Voltage Input. This pin serves as the supervised supply voltage input.
AS1916 - AS1918
2
GND
3
MRN
1
RESETN/RESET
4WDI
5VCC
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AS1916 - AS1918
Datashee t - A b s o l u t e M a x i mum R a t i n g s
5 Absolute Maximum Ratings
Stresses beyond those li sted in Table 3 may cause permanent damage to the device. These are stress ratings only, and functional operation of
the device at these or any other conditions beyond those indicated in Electrical Characteristics on page 4 is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device rel11iability.
Table 3. Absolute Maximum Ratings
Parameter Min Max Units Comments
Electrical Parameters
VCC to GND -0.3 +5.0 V
Open-Drain RESETN -0.3 +7.0 V
Push/Pull RESET, RESETN -0.3 VCC +
0.3 V
MRN, WDI to GND -0.3 VCC +
0.3 V
Input Current (VCC)20mA
Output Current (RESET, RESETN) 20 mA
Continuous Power Dissipation
Continuous Power Dissipation
(TAMB = +70ºC) 696 mW Derate 8.7mW/ºC above +70ºC
Temperature Ranges and Storage Conditions
Junction Temperature +150 ºC
Storage Temperature Range -55 +150 ºC
Package Body Temperature +260 ºC
The reflow peak soldering temperature (body temperature)
specified is in accordance with IPC/JEDEC J-STD-020
“Moisture/Reflow Sensitiv ity Cl ass ific ati on for Non-
Hermetic Solid State Surface Mount Devices”.
The lead finish for Pb-free leaded packages is matte tin
(100% Sn).
Humidity non-condensing 585%
Moisture Sensitive Level 1 Represents a max. floor life time of unlimited
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AS1916 - AS1918
Datasheet - Electrical Characteristics
6 Electrical Characteristics
VCC = +2.7 to +3.6V for AS19xx-T/S/R, VCC = +2.1 to +2.75V for AS19xx- Z/Y, VCC = +1.53 to +2.0V for AS19xx-W/V; Typical values @ T AMB
= +25ºC (unless otherwise specified).
Table 4. Electrical Characteristics
Symbol Parameter1Conditions Min Typ Max Units
TAMB Operat ing Temperature Range -40 +125 ºC
VCC Operating Voltage Range TAMB = 0 to +85ºC 1.0 3.6 V
TAMB = -40 to +125ºC 1.2 3.6
ICC VCC Supply Current
(MRN and WDI Not Connected)
VCC = +3.6V, No Load,
TAMB = -40ºC to +85ºC 5.5 12 µA
VCC = +3.6V, No Load,
TAMB = -40 to +125ºC 19
VTH VCC Reset Threshold
(VCC Falling)
TAMB = -40 to +85ºC AS19xx-T 2.994 3.08 3.154
V
TAMB = -40 to +125ºC 2.972 3.179
TAMB = -40 to +85ºC AS19xx-S 2.848 2.93 3.000
TAMB = -40 to +125ºC 2.827 3.024
TAMB = -40 to +85ºC AS19xx-R 2.556 2.63 2.693
TAMB = -40 to +125ºC 2.538 2.714
TAMB = -40 to +85ºC AS19xx-Z 2.255 2.32 2.376
TAMB = -40 to +125ºC 2.239 2.394
TAMB = -40 to +85ºC AS19xx-Y 2.129 2.19 2.243
TAMB = -40 to +125ºC 2.113 2.260
TAMB = -40 to +85ºC AS19xx-W 1.623 1.67 1.710
TAMB = -40 to +125ºC 1.612 1.723
TAMB = -40 to +85ºC AS19xx-V 1.536 1.58 1.618
TAMB = -40 to +125ºC 1.525 1.631
Reset Threshold
Temperature Coefficient 60 ppm/
ºC
Reset Threshold Hysteresis 8 x VTH mV
tRD VCC to Reset
Output Delay VCC = VTH to (VTH - 100mV) 55 µs
tRP Reset Timeout Period TAMB = -40 to +85ºC 140 215 280 ms
TAMB = -40 to +125ºC 100 320
VOL RESETN Output Low
(Push/Pull or Open-Drain)
VCC ≥ 1.0V, ISINK = 50µA,
Reset Asserted, TAMB = 0 to +85ºC 0.3
V
VCC ≥ 1.2V, ISINK = 100µA, Reset Asserted 0.3
VCC ≥ 2.55V, ISINK = 1.2mA,
Reset Asserted 0.3
VCC ≥ 3.3V, ISINK = 3.2mA,
Reset Asserted 0.4
VOH RESETN Output High
(Push/Pull Only)
VCC ≥ 1.8V, ISOURCE = 200µA,
Reset Not Asserted 0.8 x
VCC
V
VCC ≥ 3.15V, ISOURCE = 500µA,
Reset Not Asserted 0.8 x
VCC
VCC ≥ 3.3V, ISOURCE = 800µA,
Reset Not Asserted 0.8 x
VCC
ILKG Open-Drain RESETN Output Leakage
Current RESETN Not Asserted 1.0 µA
TAMB = +25ºC 0.2
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AS1916 - AS1918
Datasheet - Electrical Characteristics
VOH RESET Output High
(Push/Pull Only)
VCC ≥ 1.0V, ISOURCE = 1µA,
Reset Asserted, TAMB = 0 to +85ºC 0.8 x
VCC
V
VCC ≥ 1.50V, ISOURCE = 100µA,
Reset Asserted 0.8 x
VCC
VCC ≥ 2.55V, ISOURCE = 500µA,
Reset Asserted 0.8 x
VCC
VCC ≥ 3.3V, ISOURCE = 800µA,
Reset Asserted 0.8 x
VCC
VOL RESET Output Low
(Push/Pull Only)
VCC ≥ 1.8V, ISINK = 500µA,
Reset Asserted 0.3
V
VCC ≥ 3.15V, ISINK = 1.2mA,
Reset Asserted 0.3
VCC ≥ 3.3V, ISINK = 3.2mA,
Reset Asserted 0.4
Manual Reset Input
VIL MRN Input voltage
0.3 x
VCC V
VIH 0.7 x
VCC
MRN Minimum Input Pulse 1 µs
MRN Transient Rejection 90 ns
MRN to Reset Delay 130 ns
MRN Pullup Resistance 25 50 75 kΩ
Wa tchdog Input
tWD Watchdog Timeout Period TAMB = -40 to +85ºC 1.12 1.5 2.4 s
TAMB = -40 to +125ºC 0.80 2.60
tWDI WDI Pulse Width 2 20 ns
VIL WDI Input Voltage
0.3 x
VCC V
VIH 0.7 x
VCC
IWDI WDI Input Current WDI = VCC, Time Average 80 160 µA
WDI = 0, Time Average -20 -11
1. Over-temperature limits are guaranteed by design and not production tested. Devices tested at +25ºC.
2. Guaranteed by design and not production tested.
Note: All limits are guaranteed. The parameters with min and max values are guaranteed with production tests or SQC (Statistical Quality
Control) methods.
Table 4. Electrical Characteristics
Symbol Parameter1Conditions Min Typ Max Units
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AS1916 - AS1918
Datasheet - Typical Operating Characteristics
7 Typical Operating Characteristics
TAMB = +25ºC (unless otherwise specified).
Figure 3. Normalized Reset Thresho ld Delay vs. Figure 4. VOUT vs. VCC, VTH = 1.58V
Temperature Active-Low (Typ)
Figure 5. Reset Timeout Period vs. Temperature Figure 6. Supply Current vs. Temperature
Figure 7. VOH vs. ISOURCE; VCC = 3.2V Figure 8. VOL vs. ISINK; VCC = 3.2V
-0.50
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
5.00
5.50
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
VCC (V)
Output Voltage (V) e
0.94
0.96
0.98
1
1.02
1.04
1.06
-40 -20 0 20 40 60 80 100 120
Temperature (°C)
Reset Threshold (V) e
3
4
5
6
7
8
9
10
-50 -25 0 25 50 75 100 125
Temperature (°C)
VCC Supply Current (µA) e
VCC = 3.08V T Version
VCC = 1.58V V Version
150
160
170
180
190
200
210
220
230
240
250
-40 -20 0 20 40 60 80 100 120
Temperature (°C)
Reset Timeout Periode (ms)
2.9
2.95
3
3.05
3.1
3.15
3.2
3.25
0 0.2 0.4 0.6 0.8 1 1.2
ISOURCE (mA)
VOUT (V) ]
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
01234567
ISINK (mA)
VOUT (V) e
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AS1916 - AS1918
Datasheet - Detailed Description
8 Detailed Description
The AS1916 - AS1918 supervisory circuits were designed to generate a reset when the monitored supply voltage falls below its factory-trimmed
trip threshold (see VTH on page 4), and to maintain the reset for a minimum timeout period (see tRP on page 4) after the supply has stabilized.
The integrated watchdog timer (see Watchdog Input on page 8) helps mitigate against bad programming code or clock signals, and/or poor
peripheral response.
The active-low manual reset input (see Manual Reset Input on page 8) allows for an externally activated system reset.
8.1 RESET/RESETN
Whenever the monitored supply voltage falls below its reset threshold, the RESET output asserts low or the RESETN output asserts high. Once
the monitored voltage has stabilized, an internal timer keeps the reset asserted for the reset timeout period (tRP). After the tRP period, the
RESET/RESETN output returns to its original state (see Figure 10).
Figure 9. Functional Diagram of VCC Supervisory Application
Figure 10. Reset Timing Diagram
AS1916 - AS1918
Reset Timeout Delay
Generator
Watchdog Tra nsition
Detector Watchdog
Timer
+
–VCC
1.26V
2
GND
5
VCC
4
WDI
1
RESETN/
RESET
3
MRN
1V
tRD
tRP
tRP tRD
VTHVTH
VCC
RESETN
RESET
GND
1V
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AS1916 - AS1918
Datasheet - Detailed Description
8.2 Watchdog Input
The integrated watchdog feature can be used to monitor processor activity via pin WDI, and can detect pulses as short as 50ns. The watchd og
requires that the processor toggle the watchdog logic input at regular intervals, within a specified minimum timeout period (1.5 s, typ). A reset is
asserted for the reset timeout period. As long as reset is asserted, the timer remains cleared and is not incremented. When reset is deasserted,
the watchdog timer starts counting (Figure 11).
Note: The watchdog timer can be cleared with a reset pulse or by toggling WDI.
Figure 11. Watchdog Timing Relationship
The watchdog is internally driven low during most (87.5%) of the watchdog timeout period (see tWD on page 5) and high for the rest of the
watchdog timeout period. When pin WDI is left unconnected, this internal driver clears the watchdog timer every 1.4s. When WDI is tri-stated or
is not connected, the maximum allowable leakage current is 10µA and the maximum allowable load capacitance is 200pF.
Note: The watchdog function can be disabled by leaving pin WDI unconnected or connecting it to a tri-state output buffer.
8.3 Manual Reset Input
The active-low pin MRN is used to force a manual reset. This input can be driven by CMOS logic levels or with open-drain collector outputs.
Pulling MRN low asserts a reset which will remain asserted as long as MRN is kept low, and for the timeout period (see tRP on page 4) after
MRN goes high (140ms min). The manual reset circuitry has an internal 50kΩ pullup resistor, thus it can be left open if not used.
To create a manual-reset circuit, connect a normally open momentary switch from pin MRN to GND (see Figure 1 on page 1); external debounce
circuitry is not required in this configuration.
If MRN is driven via long cables or the device is used in a noisy environment, a 0.1µF capacitor between pin MRN and GND will provide
additional noise immunity.
tRST
The RESET signal is the inverse of the RESETN signal.
tWD
VCC
RESETN
WDI
tRP
tRP
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AS1916 - AS1918
Datasheet - Application Information
9 Application Information
9.1 Watchdog Input Current
The watchdog input is driven through an internal buffer and an internal series resistor from the watchdog timer (see Figure 11 on page 8). When
pin WDI is left unconnected (watchdog disabled), the watchdog timer is serviced within the watchdog timeout period (see tWD on page 5) by a
low-high-low pulse from the counter chain.
For minimum watchdog input current (minimum overall power consumption), pull WDI low for most of the watchdog timeout period, pulsing it low-
high-low once within the first 7/8 (87.5%) of the watchdog timeout period to reset the watchdog timer.
Note: If WDI is externally driven high for the majority of the timeout period, up to 160µA can flow into pin WDI.
9.2 Interfacing to Bi-Directional CPU Reset Pins
Since the reset output of the AS1918 is open drain, this device interfaces easily with processors that have bi-directional reset pins. Connecting
the processor reset output directly to the AS1918 RESETN pin with a single pullup resistor (see Figure 12) allows the AS1918 to assert a reset.
Figure 12. AS1918 RESETN-to-CPU Bi-Directional Reset Pin
9.3 Fast Negative-Going Transients
Fast, negative-going VCC transients normally do not require the CPU to be shutdown. The AS1916 - AS1918 are virtually immune to such
transients. Resets are issued to the CPU during power-up, powerdown, and brownout conditions.
Note: VCC transients that go 100mV below the reset threshold and last ≤ 55µs typically will not assert a reset pulse.
9.4 Valid Reset to VCC = 0
The AS1916 - AS1918 are guaranteed to operate properly down to VCC = 1V.
For AS1916 and AS1917 applications requiring valid reset levels down to VCC = 0, a pulldown resistor to active-low outputs and a pullup resistor
to active-high outputs will ensure that the reset line is valid during the interval where the reset output can no longer sink or source current.
9.5 Watchdog Tips
Careful consideration should be taken when implementing the AS1916 - AS1918 watchdog feature.
One method of supervising software code execution is to set/reset the watchdog input at different places in the code, rather than pulsing the
watchdog input high-low-high or low-high-low. This method avoids a loop condition in which the watchdog timer would continue to be reset inside
the loop, preventing the watchdog from ever timing out.
Figure 13 shows a flowchart where the input/output driving the watchdog is set high at the beginning of the routine, set low at the beginning of
every subroutine, then set high again when the routine returns to the beginning. If the routine should hang in a subroutine, the problem would
quickly be corrected, since the I/O is continually set low and the watchdog timer is allowed to time out, causing a reset or interrupt to be issued
(see Watchdog Input Current on page 9). This method results in higher averaged WDI input current over time than a case where WDI is held low
for the majority (87.5%) of the timeout period and periodically pulsing it low-high-low.
AS1918
CPU
Reset
Generator
VCC
RESETN
GND
VCC
1
RESETN
GND 2
VCC 5
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AS1916 - AS1918
Datasheet - Ordering Information
11 Ordering Information
The devices are available as the standard products shown in Table 5.
Note: All products are RoHS compliant.
Buy our products or get free samples online at ICdirect: http://www.austriamicrosystems.com/ICdirect
Technical Support is found at http://www.austriamicrosystems.com/Technical-Support
For further information and requests, please contact us mailto:sales@austriamicrosystems.com
or find your local distributor at http://www.austriamicrosystems.com/distributor
Table 5. Ordering Information
Ordering Code Marking Description Threshold Delivery Form Package
AS1916S-T ASIO Active-Low Push/Pull Supervisory Circuit with
Watchdog and Manual Reset 2.93V Tape and Reel 5-pin SOT23
AS1916R-T ASIP Active-Low Push/Pull Supervisory Circuit with
Watchdog and Manual Reset 2.63V Tape and Reel 5-pin SOT23
AS1916Z-T ASIQ Active-Low Push/Pull Supervisory Circuit with
Watchdog and Manual Reset 2.32V Tape and Reel 5-pin SOT23
AS1916V-T ASIR Active-Low Push/Pull Supervisory Circuit with
Watchdog and Manual Reset 1.58V Tape and Reel 5-pin SOT23
AS1917S-T ASIS Active High Push/Pull Supervisory Circuit with
Watchdog and Manual Reset 2.93V Tape and Reel 5-pin SOT23
AS1917R-T ASIT Active High Push/Pull Supervisory Circuit with
Watchdog and Manual Reset 2.63V Tape and Reel 5-pin SOT23
AS1917Z-T ASIU Active High Push/Pull Supervisory Circuit with
Watchdog and Manual Reset 2.32V Tape and Reel 5-pin SOT23
AS1917V-T ASIV Active High Push/Pull Supervisory Circuit with
Watchdog and Manual Reset 1.58V Tape and Reel 5-pin SOT23
AS1918S-T ASIW Active-Low Open Drain Supervisory Circuit with
Watchdog and Manual Reset 2.93V Tape and Reel 5-pin SOT23
AS1918R-T ASIX Active-Low Open Drain Supervisory Circuit with
Watchdog and Manual Reset 2.63V Tape and Reel 5-pin SOT23
AS1918Z-T ASIY Active-Low Open Drain Supervisory Circuit with
Watchdog and Manual Reset 2.32V Tape and Reel 5-pin SOT23
AS1918V-T ASIZ Active-Low Open Drain Supervisory Circuit with
Watchdog and Manual Reset 1.58V Tape and Reel 5-pin SOT23
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AS1916 - AS1918
Datasheet
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