Fan Control Device with High Frequency PWM and Temperature Monitors
Datasheet
PWM Min set to x%
PWM Min set to 0%
(x is not 0)
Temp
Temp
TMAX = TMIN
+
TMAX = TMIN
+
TRANGE
TRANGE
TMIN
TMIN
Duty
Duty
Cycle
Cycle
100%
100%
Min
spin-up
time
Note: When spin-up ends, the PWM is set to the
current calculated PWM
Figure 7.2 Automatic Fan Control
7.1.3.3
Spin Up
When a fan is being started from a stationary state (PWM duty cycle =00h), the part will cause the fan
to “spin up” by going to 100% duty cycle for a programmable amount of time to overcome the inertia
of the fan (i.e., to get the fan turning). Following this spin up time, the fan will go to the duty cycle
computed by the auto fan algorithm.
Note 7.3 The EMC2300 automatically performs the Spin Up routine upon power-up. The only
conditions that will allow the fan to be in an stationary state are if the user programs the
PWM input to 00h (in Manual Mode) or the user programs the Minimum PWM to 00h and
the corresponding temperature channel(s) are below the low temperature limit.
During spin-up, the PWM duty cycle is reported as 0%.
To limit the spin-up time and thereby reduce fan noise, the part uses feedback from the tachometers
to determine when each fan has started spinning properly. The following tachometer feedback is
included into the auto fan algorithm during spin-up.
Auto Fan operation during Spin Up:
The PWM goes to 100% duty cycle until the tachometer reading register is below the minimum limit
(see Figure 7.4), or the spin-up time expires, whichever comes first. This causes spin-up to continue
until the tachometer enters the valid count range, unless the spin up time expires. If the spin up expires
before the tachometer enters the valid range, an interrupt status bit will be set once spin-up expires.
Note that more than one tachometer may be associated with a PWM, in which case all tachometers
associated with a PWM must be in the valid range for spin-up to end.
Revision 0.2 (06-14-06)
SMSC EMC2300
DATA3S4HEET
SMSC [ SMSC CORPORATION ]
