U6813B ATMEL Corporation, U6813B Datasheet - Page 4

• Manufacturer Part Number: U6813B
• Description: U6813b Fail-safe Ic With High-side And Relay Driver
• Manufacturer: ATMEL Corporation

3. Fail-safe Functions
Table 3-1.
Notes:
4. Watchdog Description
4
wrong
VCC
ok
ok
ok
ok
ok
x
1. default state at open input
2. P-EN disable: low
3. N-EN disable: high
U6813B
wrong
Truth Table
3.3V
ok
ok
ok
ok
ok
x
wrong
WDI
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 han-
dle those fault conditions according to
Figure 4-1.
The microcontroller is monitored by a digital window watchdog which accepts an incoming trig-
ger signal of a constant frequency for correct operation. The frequency of the trigger signal can
be varied in a broad range as the watchdog’s time window is determined by external R/C com-
ponents. The following description refers to the watchdog timing diagram with tolerances (see
Figure 4-2 on page
ok
ok
ok
ok
x
x
RELI
L
H
x
x
x
x
x
(1)
Watchdog Block Diagram
OSCERR
RESET
WDC
WDI
5).
FETI
L
H
x
x
x
x
x
(1)
detector
Slope
RELO
on
off
off
off
off
x
x
Binary counter
Table 3-1
FETO
off
on
off
off
off
x
x
Dual MUX
for a maximum of system safety.
Up/down
counter
N-RES
H
H
H
H
H
L
L
RS-FF
P-RES
H
H
L
L
L
L
L
WD-OK
P-EN
H
H
H
H
L
L
L
(2)
4543B–AUTO–10/05
N-EN
H
H
H
L
L
L
L
(3)