Rainbow Electronics MAX6660 - Manual (Page 17)

MAX6660
Remote-Junction Temperature-Controlled
Fan-Speed Regulator with SMBus Interface
______________________________________________________________________________________ 17
REGISTER/
ADDRESS
FCD (1Dh = READ, 1Eh = WRITE)
COMMAND READ LIMIT/FAILURE REGISTER
Bit 7 6 5 4 3 2 1 0
POR State 0 0 0 0 0 0 0 1
Table 12. Fan Count Divisor Register (RFCD/WFCD)
Notes: This byte sets the prescalar division ratio for tachometer or current-sense feedback. (This register does not apply to the tach
signal used in the Fan-Speed register). Select this value such that the fan frequency (RPM/60 x number of poles) divided by
the FCD falls in the 33Hz to 66Hz range. See TACH IN section.
Bits 1, 0: 00 = divide by 1, 01 = divide by 2, 10 = divide by 4, 11 = divide by 8.
N
TEMPDATA
FG
4/5/6
REF FREQUENCY
8415Hz
FS
127/255
1/64 COUNTER
FTC FTCL
COMPARATOR
FCD
1/2/4/8
FAN OPEN/CLOSED
LOOP
UP/DOWN
DRIVER DAC
FAN FAIL
VFAN
FAN
TACH IN
Figure 7. MAX6660 Fan Loop Functional Diagram