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Features
* * * * * * * * *
Low Current Consumption: IDD < 100 A 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
Digital Window Watchdog Timer U5020M
Description
The digital window watchdog timer, U5020M, is a CMOS integrated circuit. In applications 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 microcontroller. 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.
Rev. 4755A-AUTO-11/03
Figure 1. Block Diagram with External Ciruit
C VDD OSC C1 Reset Input ts 10 15 10 nF 13 RC Oscillator OSC
R1 VDD
Microcontroller
16 OSC State machine 9 Enable Power-on reset POR Test logic External switching circuitry
Trigger
11
Input signal conditioning POR
Mode 12
Wake up 3-8
14 GND
2 Test
1 Test
Pin Configuration
Figure 2. Pinning SO16
1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 TS OSC GND VDD MODE TRIG RESET ENA
TM TM WAKE-UP WAKE-UP WAKE-UP
WAKE-UP WAKE-UP WAKE-UP
2
U5020M
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U5020M
Pin Description
Pin 1 2 3 to 8 Symbol TM TM WAKE-UP Function Test must not be connected Test must be connected to GND 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. Enable output (push-pull) It is used for the control of peripheral components. It is activated after the processor triggers three times correctly. 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. Trigger input (pull-up resistor) It is connected to the microprocessor's trigger signal. Mode input (pull-up resistor) The processor's mode signal initiates the switchover between the long and the short watchdog time. Supply voltage Ground, reference voltage RC oscillator Time switch input Programming pin to select different time durations for the long watchdog time.
9
ENA
10
RESET
11 12 13 14 15 16
TRIG MODE VDD GND OSC TS
Functional Description
Supply, Pin 13
The U5020M requires a stabilized supply voltage VDD = 5 V 5% to comply with its electrical 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:
1 f = -t
where t = 1.35 + 1.57 R1 (C1 + 0.01) R1 in kW, C1 in nF and t in s 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 appropriate 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%
3
4755A-AUTO-11/03
Figure 3. Period t versus R1, at C1 = 500 pF
1000.00
100.00
t (s)
4.5 V
10.00
5.0 V 5.5 V C1 = 500 pF
1.00 1 10 100 1000
R1 (k)
Figure 4. Power-up Reset and Mode Switchover
Pin 13 VDD
t0
t6
Pin 10
Reset out
t1
Mode Pin 12
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 microcontroller in its defined reset status (see Figure 4). Pin 10 has an open-drain output. 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 Figure 4) the watchdog generates a reset pulse, t 6 , and the time, t 1 , starts again. Microcontroller and watchdog are synchronized with the switchover mode time, t1, each time a reset pulse is generated.
Switch-over Mode Time, Pin 12
4
U5020M
4755A-AUTO-11/03
U5020M
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
VDD Pin 13
t0
t1
Pin 10
Reset out
t2
Mode
t3
Pin 12
Pin 11 Trigger
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 operation 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-critical 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.
5
4755A-AUTO-11/03
Figure 6. Pulse Diagram of a Correct Trigger Sequence During the Short Watchdog Time
VDD Pin 13
t0
Reset out
t1
Pin 10
t2
Mode
t3 t2
Pin 12 Pin 11
Trigger
ttrig
Enable Pin 9
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
t6
Reset out
t1
Pin 10
Wake-up
Pins 3 to 8
t4
Mode
t5
Pin 12
t2
Trigger Pin 11
Enable
Pin 9
6
U5020M
4755A-AUTO-11/03
U5020M
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 Output current Input voltage Ambient temperature range Storage temperature range
VDD IOUT VIN Tamb Tstg
6.5 2 -0.5 V to VDD + 0.5 V -40 to +85 -55 to +150
V mA V
C C
Thermal Resistance
Parameters Symbol Value Unit
Junction ambient SO16
RthJA
160
K/W
7
4755A-AUTO-11/03
Electrical Characteristics
VDD = 5 V; Tamb = -40C to +85C; reference point is ground (pin14); Figure 4 on page 4, unless otherwise specified
Parameters Test Conditions Pin Symbol Min. Typ. Max. Unit
Supply voltage Current consumption Power-on reset Power-on reset Power-on reset
Inputs
13 R1 = 66 kW Logic functions Threshold Hysteresis 13 13 13 13 3 to 8, 11, 12, 16
VDD IDD VDD VPOR Vhys VIH VIL VIN
4.5 1 3.8 100 4.0
5.5 100
V A V V mV V
Upper threshold ("1") Lower threshold ("0") Input voltage range Input current
Output Pin 9
1.0 -0.4 -20 2 4.5 0.5 2 0.5 3 96 45 4 128 201 1,112 130 124 71,970 30,002 1,200 400 40 VDD + 0.2 20
V V A mA V V mA V cycle cycle cycle cycle cycle cycle cycle cycle cycle cycle cycle cycle
Depending on pin
I IN IOUT
Maximum output current Upper output voltage ("1") Lower output voltage ("0")
Output Pin 10
IOUT = 1 mA IOUT = -1 mA
VOH VOL IOUT
Maximum output current Lower output voltage ("0")
Timing
IOUT = -1 mA Trig, Mode Wake-up 1-6 11, 12 3 to 8
VOL
Debounce period Debounce period Maximum trigger pulse period Power-up reset time Time-out period Short disable time Short enable time Long disable time Long enable time Long disable time Long enable time Reset-out time
to t1 t2 t3 Input switch = low (0) Input switch = low (0) Input switch = high (1) Input switch = high (1) 16 16 16 16 t4 t5 t4 t5 t6
8
U5020M
4755A-AUTO-11/03
U5020M
Ordering Information
Extended Type Number Package Remarks
U5020M-FP
SO16
-
Package Information
Package SO16
Dimensions in mm
10.0 9.85 5.2 4.8 3.7
1.4 0.4 1.27 8.89 16 9 0.25 0.10 0.2 3.8 6.15 5.85
technical drawings according to DIN specifications
1
8
9
4755A-AUTO-11/03
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4755A-AUTO-11/03

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