EMC2105 Datasheet, PDF (80/90 Pages) SMSC Corporation – RPM-Based High Side Fan Controller with Hardware Thermal Shutdown

RPM-Based High Side Fan Controller with Hardware Thermal Shutdown
Datasheet
Appendix B Look Up Table Operation
The EMC2105 uses a look-up table to apply a user-programmable fan control profile based on
measured temperature to the fan driver. In this look-up table, each temperature channel is allowed to
control the fan drive output independently (or jointly) by programming up to eight pairs of temperature
and drive setting entries.
The user programs the look-up table based on the desired operation. If the RPM based Fan Speed
Control Algorithm is to be used (see Section 6.6), then the user must program an RPM target for each
temperature setting of interest. Alternately, if the RPM based Fan Speed Control Algorithm is not to be
used, then the user must program a drive setting for each temperature setting of interest.
If the measured temperature on the External Diode channel meets or exceeds any of the temperature
thresholds for any of the channels, the fan output will be automatically set to the desired setting
corresponding to the exceeded temperature. In cases where multiple temperature channel thresholds
are exceeded, the highest fan drive setting will take precedence.
When the measured temperature drops to a point below a lower threshold minus the hysteresis value,
the fan output will be set to the corresponding lower set point.
The following sections show examples of how the Look Up Table is used and configured. Each Look
Up Table Example uses the Fan 1 Look Up Table Registers configured as shown in Table B.1.
STEP
1
2
3
4
5
6
7
8
TEMP 1
LUT Temp 1
Setting 1 (52h)
LUT Temp 1
Setting 2 (57h)
LUT Temp 1
Setting 3 (5Ch)
LUT Temp 1
Setting 4 (61h)
LUT Temp 1
Setting 5 (66h)
LUT Temp 1
Setting 6 (6Bh)
LUT Temp 1
Setting 7 (70h)
LUT Temp 1
Setting 8 (75h)
Table B.1 Look Up Table Format
TEMP 2
LUT Temp 2
Setting 1 (53h)
LUT Temp 2
Setting 2 (58h)
LUT Temp 2
Setting 3 (5Dh)
LUT Temp 2
Setting 4 (62h)
LUT Temp 2
Setting 5 (67h)
LUT Temp 2
Setting 6 (6Ch)
LUT Temp 2
Setting 7 (71h)
LUT Temp 2
Setting 8 (76h)
TEMP 3
LUT Temp 3
Setting 1 (54h)
LUT Temp 3
Setting 2 (59h)
LUT Temp 3
Setting 3 (5Eh)
LUT Temp 3
Setting 4 (63h)
LUT Temp 3
Setting 5 (68h)
LUT Temp 3
Setting 6 (6Dh)
LUT Temp 3
Setting 7 (72h)
LUT Temp 3
Setting 8 (77h)
TEMP 4
LUT Temp 4
Setting 1 (55h)
LUT Temp 4
Setting 2 (5Ah)
LUT Temp 4
Setting 3 (5Fh)
LUT Temp 4
Setting 4 (64h)
LUT Temp 4
Setting 5 (69h)
LUT Temp 4
Setting 6 (6Eh)
LUT Temp 4
Setting 7 (73h)
LUT Temp 4
Setting 8 (78h)
LUT DRIVE
LUT Drive
Setting 1 (51h)
LUT Drive
Setting 2 (56h)
LUT Drive
Setting 3 (5Bh)
LUT Drive
Setting 4 (60h)
LUT Drive
Setting 5 (65h)
LUT Drive
Setting 6 (6Ah)
LUT Drive
Setting 7 (6Fh)
LUT Drive
Setting 8 (74h)
B.1 Example #1
This example does not use the RPM based Fan Speed Control Algorithm. Instead, the Look Up Table
is configured to directly set a fan drive setting based on the temperature of four of its measured inputs.
The configuration is set as shown in Table B.2.
Once configured, the Look Up Table is loaded as shown in Table B.3. Table B.3 shows three
temperature configurations using the settings in Table B.3 and the final fan drive setting that the Look
Up Table will select.
Revision 1.72 (11-01-07)
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