Rev. 4755A–AUTO–11/03
Features
•Low Current Consumption: IDD < 100 µA
•RC Oscillator
•Internal Reset During Power-up and Supply Voltage Drops (POR)
•“Short” Trigger Window for Active Mode
“Long” Trigger Window for Sleep Mode
•Cyclical Wake-up of the Microcontroller in Sleep Mode
•Trigger Input
•Six Wake-up Inputs
•Reset Output
•Enable Output
Description
The digital window watchdog timer, U5020M, is a CMOS integrated circuit. In applica-
tions where safety is critical, it is especially important to monitor the microcontroller.
Normal microcontroller operation is indicated by a cyclically transmitted trigger signal,
which is received by a window watchdog timer within a defined time window.
A missing or a wrong trigger signal causes the watchdog timer to reset the microcon-
troller. The IC is tailored for microcontrollers which can work in both full-power and
sleep mode. With an additional voltage monitoring (power-on reset and supply voltage
drop reset), the U5020M offers a complete monitoring solution for microsystems in
automotive and industrial applications.
Digital Window
Watchdog Timer
U5020M
2U5020M
4755A–AUTO–11/03
Figure 1. Block Diagram with External Ciruit
Pin Configuration
Figure 2. Pinning SO16
Input signal
conditioning
OSC
POR
12
11
Power-on
reset
16
10
Mode
Trigger
RC
Oscillator
State machine
POR
OSC
Reset
Micro-
controller
Test logic
3-8 2 1
Test Test
Wake up
External
switching
circuitry
Input ts
9
14
Enable
GND
15
13
C
10 nF
R1
VDD OSC
C1
VDD
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
WAKE-UP
TM
TM
GND
VDD
MODE
TRIG
RESET
ENA
TS
OSC
WAKE-UP
WAKE-UP
WAKE-UP
WAKE-UP
WAKE-UP
3
U5020M
4755A–AUTO–11/03
Functional
Description
Supply, Pin 13 The U5020M requires a stabilized supply voltage VDD = 5 V ±5% to comply with its elec-
trical characteristics.
An external buffer capacitor of C = 10 nF may be connected between pin 13 and GND.
RC Oscillator, Pin 15 The clock frequency, f, can be adjusted by the components R1 and C1 according to the
formula:
where t = 1.35 + 1.57 R1 (C1 + 0.01)
R1 in kW, C1 in nF and t in µs
The clock frequency determines all time periods of the logic part as shown in the table
“Electrical Characteristics” under the subheading “Timing” on page 8. With an appropri-
ate component selection, the clock frequency, f, is nearly independent of the supply
voltage as shown in Figure 3 on page 4.
Frequency tolerance Dfmax = 10% with R1 ±1%, C1 = ±5%
Pin Description
Pin Symbol Function
1 TM Test must not be connected
2 TM Test must be connected to GND
3 to 8 WAKE-UP
Wake-up inputs (pull-down resistor)
There are six digitally debounced wake-up inputs. During the long trigger mode each signal slope at the
inputs initiates a reset pulse at pin 10.
9ENA
Enable output (push-pull)
It is used for the control of peripheral components. It is activated after the processor triggers three times
correctly.
10 RESET
Reset output (open drain)
Resets the processor in the case of a trigger error or if a wake-up pulse occurs during the long watchdog
period.
11 TRIG Trigger input (pull-up resistor)
It is connected to the microprocessor’s trigger signal.
12 MODE Mode input (pull-up resistor)
The processor’s mode signal initiates the switchover between the long and the short watchdog time.
13 VDD Supply voltage
14 GND Ground, reference voltage
15 OSC RC oscillator
16 TS Time switch input
Programming pin to select different time durations for the long watchdog time.
f1
t
---=
4U5020M
4755A–AUTO–11/03
Figure 3. Period t versus R1, at C1 = 500 pF
Figure 4. Power-up Reset and Mode Switchover
Supply Voltage
Monitoring, Pin 10
The integrated power-on reset (POR) circuitry sets the internal logic to a defined basic
status and generates a reset pulse at the reset output, pin 10, during ramp-up of the
supply voltage and in the case of voltage drops of the supply. A hysteresis in the POR
threshold prevents the circuit from oscillating. During ramp-up of the supply voltage, the
reset output stays active for a specified period of time (t0) in order to bring the microcon-
troller in its defined reset status (see Figure 4). Pin 10 has an open-drain output.
Switch-over Mode Time,
Pin 12
The switch-over mode time enables the synchronous operation of microcontroller and
watchdog. When the power-up reset time has elapsed, the watchdog has to be switched
to monitoring mode by the microcontroller by a “low” signal transmitted to the mode pin
(pin 12) within the time-out period, t1. If the low signal does not occur within t1, (see Fig-
ure 4) the watchdog generates a reset pulse, t6, and the time, t1, starts again.
Microcontroller and watchdog are synchronized with the switchover mode time, t1, each
time a reset pulse is generated.
1.00
10.00
100.00
1000.00
1 10 100 1000
t (µs)
C1 = 500 pF
4.5 V
5.5 V
5.0 V
R1 (kΩ)
t0
Reset out
Mode
VDD
Pin 13
Pin 10
Pin 12
t1
t6
5
U5020M
4755A–AUTO–11/03
Microcontroller in Active Mode
Monitoring with the “Short”
Trigger Window
After the switch-over mode the watchdog operates in short watchdog mode and expects
a trigger pulse from the microcontroller within the defined time window, t3, (enable time).
The watchdog generates a reset pulse which resets the microcontroller if
• the trigger pulse duration is too long
• the trigger pulse is within the disable time, t2
• there is no trigger pulse
Figure 5 shows the pulse diagram with a missing trigger pulse.
Figure 5. Pulse Diagram with no Trigger Pulse During the Short Watchdog Time
Figure 6 on page 6 shows a correct trigger sequence. The positive edge of the trigger
signal starts a new monitoring cycle with the disable time, t2. To ensure correct opera-
tion of the microcontroller, the watchdog needs to be triggered three times correctly
before it sets its enable output. This feature is used to activate or deactivate safety-criti-
cal components which have to be switched to a certain condition (emergency status) in
the case of a microcontroller malfunction. As soon as there is an incorrect trigger
sequence, the enable signal is reset and it takes a sequence of three correct triggers
before enable is reset.
Microcontroller in Sleep Mode
Monitoring with the “Long”
Trigger Window
The long watchdog mode allows cyclical wake-up of the microcontroller during sleep
mode. As in short watchdog mode, there is a disable time, t4, and an enable time, t5, in
which a trigger signal is accepted. The watchdog can be switched from the short trigger
window to the long trigger window with a “high” potential at the mode pin (pin 12). In
contrast to the short watchdog mode, the time periods are now much longer and the
enable output remains inactive so that other components can be switched off to effect a
further decrease in current consumption. As soon as a wake-up signal at one of the 6
wake up inputs (pins 3 to 8) is detected, the long watchdog mode ends, a reset pulse
wakes-up the sleeping microcontroller and the normal monitoring cycle starts with the
mode switch-over time.
By means of a low or high potential at pin 16 (time switch), two values for the long
watchdog time can be selected.
t0
VDD
Mode
Trigger
Reset out
Pin 11
Pin 12
Pin 10
Pin 13
t1
t2t3
6U5020M
4755A–AUTO–11/03
Figure 6. Pulse Diagram of a Correct Trigger Sequence During the Short Watchdog Time
Figure 7 shows the switch-over from the short to the long watchdog mode. The wake-up
signal during the enable time, t5, activates a reset pulse, t6.
The watchdog can be switched back from the long to the short watchdog mode with a
low potential at the mode pin (pin 12).
Figure 7. Pulse Diagram of the Long Watchdog Time
VDD
Reset out
Mode
Trigger
Enable
t0
Pin 9
Pin 11
Pin 12
Pin 10
Pin 13
t1
t2
t3t2
ttrig
t2
Wake-up
Enable
Mode
Trigger
Reset out
Pin 9
Pin 11
Pin 12
Pins 3 to 8
Pin 10
t4t5
t6t1
7
U5020M
4755A–AUTO–11/03
Application Hint In order to prevent the IC from an undesired reset output signal which may be caused by
transcients on the supply under certain conditions, a PC board connection from pin 2 to
GND is strongly recommended.
Absolute Maximum Ratings
Stresses beyond 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 beyond those indicated in the operational sections of this
specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Parameters Symbol Value Unit
Supply voltage VDD 6.5 V
Output current IOUT ±2 mA
Input voltage VIN -0.5 V to VDD + 0.5 V V
Ambient temperature range Tamb -40 to +85 °C
Storage temperature range Tstg -55 to +150 °C
Thermal Resistance
Parameters Symbol Value Unit
Junction ambient SO16 RthJA 160 K/W
8U5020M
4755A–AUTO–11/03
Electrical Characteristics
VDD = 5 V; Tamb = -40°C to +85°C; reference point is ground (pin14); Figure 4 on page 4, unless otherwise specified
Parameters Test Conditions Pin Symbol Min. Typ. Max. Unit
Supply voltage 13 VDD 4.5 5.5 V
Current consumption R1 = 66 kW 13 IDD 100 µA
Power-on reset Logic functions 13 VDD 1V
Power-on reset Threshold 13 VPOR 3.8 V
Power-on reset Hysteresis 13 Vhys 100 mV
Inputs 3 to 8, 11, 12, 16
Upper threshold (“1”) VIH 4.0 V
Lower threshold (“0”) VIL 1.0 V
Input voltage range VIN -0.4 VDD +
0.2 V
Input current Depending on pin I IN -20 20 µA
Output Pin 9
Maximum output current IOUT 2mA
Upper output voltage (“1”) IOUT = 1 mA VOH 4.5 V
Lower output voltage (“0”) IOUT = -1 mA VOL 0.5 V
Output Pin 10
Maximum output current IOUT 2mA
Lower output voltage (“0”) IOUT = -1 mA VOL 0.5 V
Timing
Debounce period Trig, Mode 11, 12 3 4 cycle
Debounce period Wake-up 1-6 3 to 8 96 128 cycle
Maximum trigger pulse period 45 cycle
Power-up reset time to201 cycle
Time-out period t11,112 cycle
Short disable time t2130 cycle
Short enable time t3124 cycle
Long disable time Input switch = low (0) 16 t471,970 cycle
Long enable time Input switch = low (0) 16 t530,002 cycle
Long disable time Input switch = high (1) 16 t41,200 cycle
Long enable time Input switch = high (1) 16 t5400 cycle
Reset-out time t640 cycle
9
U5020M
4755A–AUTO–11/03
Package Information
Ordering Information
Extended Type Number Package Remarks
U5020M-FP SO16 –
technical drawings
according to DIN
specifications
Package SO16
Dimensions in mm 10.0
9.85
8.89
0.4
1.27
1.4
0.25
0.10
5.2
4.8
3.7
3.8
6.15
5.85
0.2
16 9
18
Printed on recycled paper.
Disclaimer: Atmel Corporation makes no warranty for the use of its products, other than those expressly contained in the Company’s standard
warranty which is detailed in Atmel’s Terms and Conditions located on the Company’s web site. The Company assumes no responsibility for any
errors which may appear in this document, reserves the right to change devices or specifications detailed herein at any time without notice, and
does not make any commitment to update the information contained herein. No licenses to patents or other intellectual property of Atmel are
granted by the Company in connection with the sale of Atmel products, expressly or by implication. Atmel’s products are not authorized for use
as critical components in life support devices or systems.
Atmel Corporation Atmel Operations
2325 Orchard Parkway
San Jose, CA 95131, USA
Tel: 1(408) 441-0311
Fax: 1(408) 487-2600
Regional Headquarters
Europe
Atmel Sarl
Route des Arsenaux 41
Case Postale 80
CH-1705 Fribourg
Switzerland
Tel: (41) 26-426-5555
Fax: (41) 26-426-5500
Asia
Room 1219
Chinachem Golden Plaza
77 Mody Road Tsimshatsui
East Kowloon
Hong Kong
Tel: (852) 2721-9778
Fax: (852) 2722-1369
Japan
9F, Tonetsu Shinkawa Bldg.
1-24-8 Shinkawa
Chuo-ku, Tokyo 104-0033
Japan
Tel: (81) 3-3523-3551
Fax: (81) 3-3523-7581
Memory
2325 Orchard Parkway
San Jose, CA 95131, USA
Tel: 1(408) 441-0311
Fax: 1(408) 436-4314
Microcontrollers
2325 Orchard Parkway
San Jose, CA 95131, USA
Tel: 1(408) 441-0311
Fax: 1(408) 436-4314
La Chantrerie
BP 70602
44306 Nantes Cedex 3, France
Tel: (33) 2-40-18-18-18
Fax: (33) 2-40-18-19-60
ASIC/ASSP/Smart Cards
Zone Industrielle
13106 Rousset Cedex, France
Tel: (33) 4-42-53-60-00
Fax: (33) 4-42-53-60-01
1150 East Cheyenne Mtn. Blvd.
Colorado Springs, CO 80906, USA
Tel: 1(719) 576-3300
Fax: 1(719) 540-1759
Scottish Enterprise Technology Park
Maxwell Building
East Kilbride G75 0QR, Scotland
Tel: (44) 1355-803-000
Fax: (44) 1355-242-743
RF/Automotive
Theresienstrasse 2
Postfach 3535
74025 Heilbronn, Germany
Tel: (49) 71-31-67-0
Fax: (49) 71-31-67-2340
1150 East Cheyenne Mtn. Blvd.
Colorado Springs, CO 80906, USA
Tel: 1(719) 576-3300
Fax: 1(719) 540-1759
Biometrics/Imaging/Hi-Rel MPU/
High Speed Converters/RF Datacom
Avenue de Rochepleine
BP 123
38521 Saint-Egreve Cedex, France
Tel: (33) 4-76-58-30-00
Fax: (33) 4-76-58-34-80
Literature Requests
www.atmel.com/literature
4755A–AUTO–11/03
© Atmel Corporation 2003. All rights reserved.
Atmel® and combinations thereof are the registered trademarks of Atmel Corporation or its subsidiaries.
Other terms and product names may be the trademarks of others.
