EMC2301 Standard Microsystems Corp., EMC2301 Datasheet - Page 20

• Manufacturer Part Number: EMC2301
• Description: Rpm-based Pwm Fan Controller
• Manufacturer: Standard Microsystems Corp.

RPM-Based PWM Fan Controller
Datasheet
100%
(optional)
30% through 65%
Fan Step
New Target Count
Algorithm controlled drive
Prev Target
Count = FFh
¼ of Spin Up Time
Update Time
Spin Up Time
Check TACH
Target Count
Target Count
Reached
Changed
Figure 4.2 Spin Up Routine
4.7
Ramp Rate Control
The Fan Driver can be configured with automatic ramp rate control. Ramp rate control is accomplished
by adjusting the drive output settings based on the Maximum Fan Step Register settings and the
Update Time settings.
If the RPM-based Fan Speed Control Algorithm is used, then this ramp rate control is automatically
used. The user programs a maximum step size for the fan drive setting and an update time. The
update time varies from 100ms to 1.6s while the fan drive maximum step can vary from 1 count to 31
counts.
When a new fan drive setting is entered, the delta from the next fan drive setting and the previous fan
drive setting is determined. If this delta is greater than the Max Step settings, then the fan drive setting
is incrementally adjusted every 100ms to 1.6s as determined by the Update Time until the target fan
drive setting is reached. See
Figure
4.3.
Revision 1.2 (03-22-10)
20
SMSC EMC2301
DATASHEET