U5021M_05 Datasheet, PDF (3/11 Pages) ATMEL Corporation – Digital Window Watchdog Timer

U5021M
3. Pin Description
Pin
Symbol Function
Wake-up input (pull-down resistor)
1
WAKE-UP There is one digitally debounced wake-up input. During the long watchdog window, each signal slope at
the input initiates a reset pulse at pin 5.
2
TRIG
Trigger input (pull-up resistor)
It is connected to the microprocessor’s trigger signal.
3
MODE
Mode input (pull-up resistor)
The processor’s mode signal initiates the switchover between the long and the short watchdog time.
Enable output (push-pull)
4
ENA
It is used for the control of peripheral components. It is activated after the processor triggers three times
correctly.
Reset output (open drain)
5
RESET Resets the processor in the case of a trigger error or if a wake-up pulse occurs during the long watchdog
period.
6
VDD
Supply voltage
7
GND
Ground, reference voltage
8
OSC
RC oscillator
4. Functional Description
4.1 Supply Voltage, Pin 6
The U5021M requires a stabilized supply voltage V_DD = 5 V ±5% to comply with its electrical
characteristics.
An external buffer capacitor of C = 10 nF may be connected between pin 6 and GND.
4.2 RC Oscillator, Pin 8
The clock frequency, f, can be adjusted by the components R₁ and C₁ according to the formula:
f = ¹--
t
where t = 1.35 + 1.57 R₁ (C₁ + 0.01)
R₁ in kΩ, 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 9. With an appropriate component
selection, the clock frequency, f, is nearly independent of the supply voltage as shown in Figure
4-1 on page 4.
Frequency tolerance ∆f_max = 10% with R₁ ±1%, C₁ = ±5%
3
4756D–AUTO–11/05