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PDF U6813B Data sheet ( Hoja de datos )
| Número de pieza | U6813B | |
| Descripción | Fail-safe IC with High-side and Relay Driver | |
| Fabricantes | ATMEL Corporation | |
| Logotipo |  |
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Features
• Digital Self-supervising Watchdog with Hysteresis
• One 150-mA Output Driver for Relay
• One High-side Driver for N-channel Power FET
• Positive and Negative Enable Output
• Positive and Negative Reset Output
• Over/Under-voltage Detection
• Relay and Power FET Outputs Protected Against Standard Transients and 55-V Load
Dump
Description
The function of microcontrollers in safety-critical applications (e.g., anti-lock systems)
needs to be monitored permanently. Usually, this task is accomplished by an indepen-
dent watchdog timer. The monolithic IC U6813B, designed in bipolar technology and
qualified according to the needs of the automotive industry, includes such a watchdog
timer and provides additional features for added value. With the help of integrated
driver stages, it is easy to control safety-related functions of a relay and of an N-chan-
nel power MOSFET in high-side applications. In case of a microcontroller malfunction
or supply-voltage anomalies, the U6813B provides positive and negative reset and
enable output signals. This flexibility guarantees a broad range of applications. The
U6813B is based on of Atmel’s fail-safe ICs U6808B and U6809B.
Figure 1. Block Diagram
Fail-safe IC with
High-side and
Relay Driver
U6813B
3.3 V 16
VCC 14
3.3-V under- and
overvoltage detect.
Bandgap
reference
2.44 V
Reset
debounce
fosc
Power-on
reset
Reset
delay
fosc
RELI 13
FETI 12
WDI 11
5-V under- and
overvoltage detect.
19k
19k
Watchdog
19k
15
SGND
2
GND
Internal
oscillator
fosc
RC-
oscillator
supervisor
RC
oscillator
10
WDC
VCC
3 P-RES
4 N-RES
Current
limitation
VCC
VCC
FET
output
8 CAPI
1 RELO
6 N-EN
5 P-EN
9 FETO
7 VS
Rev. 4543A–AUTO–05/02
1
1 page  
Watchdog Window
Calculation
U6813B
Example with recommended values
Cosc = 6.8 nF (should be preferably 10%, NPO)
Rosc = 36 kW (can be 5%, Rosc < 200 kW due to leakage current and humidity)
RC oscillator
tWDC (s) = 10-3 [Cosc (nF) [(0.00078 Rosc (kW)) + 0.0005]]
fWDC (Hz) = 1 / (tWDC)
Watchdog WDI
fWDI (Hz) = 0.01 fWDC
tWDC = 200 µs ® fWDC = 5 kHz
fWDI = 50 Hz ® tWDI = 20 ms
WDI pulse width for fault detection after 3 pulses:
Upper watchdog window
Minimum: 169/ fWDC = 33.8 ms -> fWDC/ 169 = 29.55 Hz
Maximum: 170/ fWDC = 34 ms -> fWDC/ 170 = 29.4 Hz
Lower watchdog window
Minimum: 79/ fWDC = 15.8 ms -> fWDC / 79 = 63.3 Hz
Maximum: 80/ fWDC = 16 ms -> fWDC / 80 = 62.5 Hz
WDI dropouts for immediate fault detection:
Minimum: 250/ fWDC = 50.0 ms
Maximum: 251/ fWDC = 50.2 ms
Remarks to reset relay
The duration of the over- or undervoltage pulses determines the enable- and reset out-
puts. A pulse duration shorter than the debounce time has no effect on the outputs. A
pulse longer than the debounce time results in the first reset delay. If a pulse appears
during this delay, a second delay time is triggered. Therefore, the total reset delay time
can be longer than specified in the data sheet.
4543A–AUTO–05/02
5
5 Page 
Timing Diagrams
U6813B
Figure 6. Watchdog in Too-fast Condition
5V
WDI
0V
Normal operation
WDI too fast
V Batt
RELO
0V
V Batt
FETO
0V
5V
P-EN
0V
5V
N-EN
0V
Normal operation
Don't care
14195
Figure 7. Watchdog in Too-slow Condition
Normal operation
5V
WDI
0V
WDI too slow
V Batt
RELO
0V
V Batt
FETO
0V
5V
P-EN
0V
5V
N-EN
0V
Normal operation
Don't care
14196
4543A–AUTO–05/02
11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet U6813B.PDF ] | |
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