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ATMEL Corporation |
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
Pin Configuration
Figure 2. Pinning SO16
RELO
GND
P-RES
N-RES
P-EN
N-EN
VS
CAPI
1
2
3
4
5
6
7
8
16 3.3V
15 SGND
14 VCC
13 RELI
12 FETI
11 WDI
10 WDC
9 FETO
Pin Description
Pin Symbol
1 RELO
2 GND
3 P-RES
4 N-RES
5 P-EN
6 N-EN
7 VS
8 CAPI
9 FETO
10 WDC
11 WDI
12 FETI
13 RELI
14 VCC
15 SGND
16 3.3V
Description
Open-collector output driver
Supply
Digital output
Digital output
Digital output
Digital output
Battery supply
Analog input
Power FET output
Analog input
Digital input
Digital input
Digital input
Supply
Supply
Analog input
Function
Fail-safe relay driver
General ground
Positive reset signal
Negative reset signal
Positive enable signal
Negative enable signal
Voltage for charge pump
Input bootstrap capacitor
High voltage for N-channel FET
External RC for watchdog timer
Watchdog trigger signal
Activation of power FET
Activation of relay driver
5-V supply
Sense ground, reference for VCC and 3.3 V
3.3-V supply
Type
Driver on: L
Reset: H
Reset: L
Enable: H
Enable: L
Pulse sequence
FET on: H
Driver on: H
Fail-safe Functions
A fail-safe IC has to maintain its monitoring function even if there is a fault condition at
one of the pins (e.g., short circuit), ensuring that a microcontroller system does not
reach a “critical status”. A critical status means, for example, if the system is not able to
switch off the relay or disable the power MOSFET, or if the system is not able to provide
a signal to the microcontroller via ENABLE- and RESET-outputs in the case of a fault
condition. The U6813B is designed to handle those fault conditions according to Table 1
for a maximum of system safety.
2 U6813B
4543A–AUTO–05/02
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