Rainbow Electronics MAX34441 - Manual (Page 25)

PMBus 5-Channel Power-Supply Manager
and Intelligent Fan Controller
MAX34441
25
Figure 3. Fan Spin-Up
Fan Spin-Up
Figure 3 shows the fan spin-up process. When the fan is
spinning up, the number of revolutions is checked every
200ms for up to 2s. When the number of cumulated revo-
lutions is greater than or equal to the spin-up relaxation
criteria, the fan passes spin-up. If the fan has a locked
rotor output, fan spin-up passes when the locked rotor
signal is no longer asserted.
When spin-up passes, the device forces the fan PWM
with a 40% duty cycle. The 40% duty cycle is maintained
until the next temperature conversion is completed,
which occurs once a second. After the temperature con-
version, the device enters either manual mode operation
or automatic operation using MFR_FAN_LUT.
100%
SPIN-UP
CRITERIA MET
AUTOMATIC
SPIN-UP
ENABLED
AUTOMATIC
SPIN-UP
DISABLED
ALWAYS RETURN TO 40% DUTY
CYCLE AFTER AUTOMATIC SPIN-UP
BEFORE BEGINNING PWM RAMP
(EVEN IF BEYOND 1 SECOND)
INITIAL TARGET PWM OR
RPM DETERMINED AFTER
TEMPERATURE CONVERSION
90%
80%
70%
60%
50%
40%
30%
20%
10%
0 0.2 0.4 0.6 0.8
TIME (SECONDS)
1.0 1.2 1.4
RAMP PWM TO TARGET PWM OR RPM
(CONSTRAINED BY THE RAMP BITS)