RPM-Based Fan Controller with Multiple Temperature Zones & Hardware Thermal Shutdown
Datasheet
The EMC2113 monitors the TACH signal in real time. It constantly updates the tachometer
measurement by reporting the number of clocks between a user programmed number of edges on the
TACH signal (see Table 7.34, "Minimum Edges for Fan Rotation").
Using the Tach Period Measurement method provides fast response times for the RPM-based Fan
Speed Control Algorithm and the data is presented as a count value that represents the fan RPM
period. When this method is used, all fan target values must be input as a count value for proper
operation.
APPLICATION NOTE: The Tach Period Measurement method works independently of the drive settings. If the
device is put into Direct Setting and the fan drive is set at a level that is lower than the fan
can operate (including zero drive), then the tachometer measurement may signal a Stalled
Fan condition and assert an interrupt.
6.7.1
Stalled Fan
A Stalled fan is detected if the tach counter exceeds the user-programmable Valid TACH Count setting.
The EMC2113 will flag the fan as stalled and trigger an interrupt.
If the RPM-based Fan Speed Control Algorithm is enabled, the algorithm will automatically attempt to
restart the fan until it detects a valid tachometer level or is disabled.
The FAN_STALL Status bit indicates that a stalled fan was detected. This bit is checked conditionally
depending on the mode of operation.
When the Direct Setting Mode or Direct Setting with LUT Mode are enabled, the FAN_STALL
interrupt will be masked for the duration of the programmed Spin Up Time (see Table 7.44, "Spin
Time"). This is to allow the fan opportunity to reach a valid speed without generating unnecessary
interrupts.
In Direct Setting Mode or Direct Setting with LUT Mode, whenever the drive value is changed from
00h, the FAN_STALL interrupt will be masked for the duration of the programmed Spin Up Time to
allow the fan opportunity to reach a valid speed without generating unnecessary interrupts.
In Direct Setting Mode or Direct Setting w/ LUT Mode, and the tachometer measurement is using
the Tach Period Measurement method, then whenever the TACH Reading Register value exceeds
the Valid TACH Count Register setting, the FAN_STALL status bit will be set.
When using the RPM-based Fan Speed Control Algorithm (either FSC Mode or LUT with FSC
Mode), the stalled fan condition is checked whenever the Update Time is met and the fan drive
setting is updated. It is not a continuous check.
6.7.2
Aging Fan or Invalid Drive Detection
The EMC2113 contains circuitry that detects that the programmed fan speed can be reached by the
fan. If the target fan speed cannot be reached within a user defined band of tach counts at maximum
drive then the DRIVE_FAIL status bit is set and the ALERT pin is asserted. This is useful to detect
aging fan conditions (where the fan’s natural maximum speed degrades over time) or incorrect fan
speed settings.
6.8
Spin Up Routine
The EMC2113 also contains programmable circuitry to control the spin up behavior of the fan driver
to ensure proper fan operation. The Spin Up Routine is initiated under the following conditions when
the Tach Period Measurement method of tach measurement is used: This applies to both the RPM-
based Fan Speed Control Algorithm mode, or Direct Setting mode (with or without the Look Up Table
- when enabled).
1. The TACH Target Register value changes from a value of FFh to a value that is less than the Valid
TACH Count (see Section 7.30, "Valid TACH Count Register").
2. The RPM-based Fan Speed Control Algorithm’s measured TACH Reading Register value is greater
than the Valid TACH Count setting.
SMSC EMC2113
Revision 1.2 (10-08-09)
DATA3S1HEET
SMSC [ SMSC CORPORATION ]
