U6808B-MFP Atmel, U6808B-MFP Datasheet - Page 5

• Manufacturer Part Number: U6808B-MFP
• Description: IC FAILSAFE W/RELAY DRVR 8-SOIC
• Manufacturer: Atmel

Specifications of U6808B-MFP

• Applications: Automotive
• Current - Supply: 15mA
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Explanation
Watchdog Window
Calculation
Example with Recommended
Values
RC Oscillator
Watchdog WDI
WDI Pulse Width for Fault
Detection after 3 Pulses
WDI Dropouts for Immediate
Fault Detection
Figure 5. Watchdog Timing Diagram with Tolerances
Reset Delay
4707A–AUTO–05/03
Time/s
Update rate is too
fast
79/f
WDC
Update rate is
either too fast or
good
80/f
In each block, the first character represents the state of the counter. The second nota-
tion indicates the fault status of the counter. A fault status is indicated by an F and a no
fault status is indicated by an NF. When the watchdog is powered up initially, the
counter starts out at the 0/F block (initial state). Good indicates that a pulse has been
received whose width resides within the timing window. Bad indicates that a pulse has
been received whose width is either too short or too long.
C
R
t
f
f
t
f
Upper watchdog window
Minimum: 169/f
Maximum: 170/f
Lower watchdog window
Minimum: 79/f
Maximum: 80/f
Minimum:
Maximum:
The duration of the over or undervoltage pulses determines the enable and reset output.
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.
WDC
WDC
WDI
WDC
WDI
Watchdog window
update rate is good
WDC
osc
osc
(Hz) =0.01 ´ f
= 100 Hz ® t
(s) = 10
(Hz) = 1/(t
= 39 k W (may be 5%, Rosc < 100 k W due to leakage current and humidity)
= 3.3 nF (should be preferably 10%, NPO)
= 100 µs ® f
-3
250/f
251/f
´ [C
WDC
WDC
WDC
WDC
WDC
169/f
WDC
WDI
WDC
osc
)
WDC
WDC
= 7.9 ms ® f
= 8.0 ms ® f
= 16.9 ms ® f
= 17.0 ms ® f
Update rate is
either too slow or
good
= 10 ms
(nF) ´ [(0.00078 ´ R
WDC
= 10 kHz
= 25 ms
= 25.1 ms
WDC
WDC
WDC
WDC
170/f
/79 = 126.6 Hz
/80 = 125.0 Hz
Update rate is too
slow
/169 = 59.1 Hz
/170 = 58.8 Hz
WDC
osc
(k W )) + 0.0005]]
250/f
Update rate is
either too slow or
pulse has
dropped out
WDC
Pulse has
dropped out
U6808B
251/f
WDC
5