MAX6620ATI MAXIM [Maxim Integrated Products], MAX6620ATI Datasheet - Page 21

• Manufacturer Part Number: MAX6620ATI
• Description: Quad Linear Fan-Speed Controller
• Manufacturer: MAXIM [Maxim Integrated Products]

BIT
4
1
0
3
2
R/W
R/W
R/W
R/W
—
—
Fan_ Dynamics Registers (06h, 07h, 08h, 09h)—POR = 0100 1100 (continued)
______________________________________________________________________________________
Fan_ DAC Rate-of-Change:
The fan drive voltage (at the DACFB_ inputs) varies from 0 to full scale in 512 increments. The rate-of-
change bits determine the time interval between output voltage increments/decrements. In RPM mode, a
setting of 0 would result in an unstable feedback loop, so a default value of 0.0625 is in effect when 0 is
selected.
Regardless of the settings, there are a few cases for which the rate-of-change is always 0:
Reserved
Reserved
•
•
•
•
When a target TACH count of 2047 (7FF) is selected, the fan drive voltage immediately goes to 0V. A
When a target fan drive voltage of 0V is selected, the drive voltage immediately goes to 0V. Again, it is
When the current drive level is 0 in DAC mode, selecting a new target fan drive voltage will immediately
When the current drive level is 0 in RPM mode, selecting a new target TACH count that is less than 2047
full-scale target count is assumed to mean that the intent is to shut down the fan, and going directly to 0
drive avoids the possibility of loss of control-loop feedback at high TACH counts. If a slow- speed
decrease toward 0 is desired, a target TACH count at the slowest practical value for the fan should be
chosen. Once that count has been reached, selecting a count of 2047 (7FF) will then take the drive
immediately to 0V.
assumed that the intent is to shut down the fan. If a slow-speed decrease toward 0 is desired, a target
fan drive voltage of the slowest practical value for the fan in question should be chosen. Once that drive
voltage has been reached, selecting a target value of 0 will then take the drive immediately to 0V.
take the voltage to that value. The fan will spin-up first if spin-up is enabled.
(7FF) will immediately take the drive voltage to the value in the Fan_ Target Drive Voltage register. From
this value, the drive voltage will increment as needed to achieve the desired TACH count. The fan will
spin-up first if spin-up is enabled.
D4:D2
000
001
010
011
100
101
110
111
Quad Linear Fan-Speed Controller
TIME BETWEEN OUTPUT VOLTAGE
DAC MODE
0
INCREMENTS (s)
0.0625 (default)
0.015625
0.03125
0.125
0.25
0.5
1.0
FUNCTION
RPM MODE
0.0625
TIME FROM 33%
TO 100%
160
320
640
(s)
10
20
40
80
0
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