MAX6620
Quad Linear Fan-Speed Controller
17
Maxim Integrated
Global Configuration Register (00h)—POR = 0000 0XXX (continued)
BIT R/W FUNCTION
2
1
R/W
I
2
C Watchdog:
When active, the watchdog monitors SDA and SCL for valid I
2
C transactions. If there are no valid
transactions between the master and the MAX6620 within the watchdog period, all fan output voltages
will go to full-scale drive voltage.
If the watchdog times out and valid I
2
C transactions begin to occur again, operation will resume with the
previous DAC value. The master can then program the output voltages, target TACH counts, or other
functions in the normal manner.
When the watchdog function is active, ensure that the master communicates to the MAX6620
periodically, for example reading a status register.
The POR state is set by the state of the WD_START pin at power-up.
D2:D1 I
2
C WATCHDOG PERIOD (s) POR CONDITION
00 Inactive (no watchdog) WD_START = GND
01 2 —
10 6 —
11 10 WD_START = V
CC
0 R
I
2
C Watchdog Status:
0 = I
2
C transactions occurred within watchdog period
1 = time between I
2
C transaction exceeds watchdog period
This bit is cleared by I
2
C read from this register.
