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SMSC EMC2102 [1], Note:, 6.2.1General Setup, Figure 6.3 Fan TACH Measurement With EMC2102

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Fan Speed Control with the EMC2102 Device

Note: Although users can set the number of edges (in register 52h) to either 3, 5, 7 or 9, it is strongly recommended using the default value 5 while driving a 2-pole DC fan. This equal to one complete fan revolution for a 2-pole fan.

5 EDGES

3 EDGES

Fan Tach Signal

7 EDGES

32.768kHz

Clock

n-EDGE WINDOW

TWINDOW

Figure 6.3 Fan TACH Measurement With EMC2102

ChipMan translates TACH counts to the RPM value and displays the fan speed. For applications not using ChipMan software, the following equation can be used to convert the TACH Reading values to the real RPM speeds.

						where:
	RPM =	EDGES − 1		983040	* m	EDGES = number of edges set by register 52h[4:3]
			*
		Poles		COUNT		COUNT = TACH Reading (58h) value	[1]

Poles = number of pole pairs in the DC fan

m = factor defined by LIMIT2K (52h[6])

(m = 1 for 500 rpm and m = 4 for 2000 rpm)

6.2Characterizing a DC Fan with EVB-EMC2102 and ChipMan

As a very important component in the closed-loop, the DC fan’s characteristics have a great impact on the control system’s performance. Using the EVB-EMC2102 and ChipMan software tool, a 5V DC fan’s characteristics can be easily tested.

In general, the following parameters need to be characterized:

Minimum Startup Speed

Stall Speed

Minimum Valid TACH Speed

Maximum Fan Speed

Spin-up Level (i.e., rpm60 and rpm75. Refer to Section 5.3.1, "Fan Control Parameters" for more details)

6.2.1General Setup

Setup the system and make sure the hardware and software are working as discussed in Section 5.1, "Experiment 1 - Manual Fan Control".

Unplug the on-board DC fan from connector P1

Connect the DC fan to be tested to P1 (refer to EVB-EMC2102 User Manual for the DC fan connector pinouts)

Revision 0.2 (09-17-07)

USER MANUAL

SMSC EMC2102

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Contents

USER MANUAL Page Page Page Page Page Figure 4.1 EMC2102 Fan Control Evaluation System Figure 4.2 EVB-EMC2102Board 5.1.1ChipMan Installation 5.1.2Setting Up the ChipMan Figure 5.1 ChipMan Message for First Operation Note: Figure 5.2 ChipMan Device Selection Window Figure 5.3 Selecting the Device and Master Controller Type Figure 5.4 ChipMan Operation Window Notes: Figure 5.5 Changing Fan Speed 5.1.3Plotting From ChipMan Figure 5.6 Plotting from the ChipMan Figure 5.7 Plot Windows Figure 5.8 Plot Examples 5.2.1Getting Started 5.2.2Basic RPM Based Fan Control Figure 5.9 Plots for Proper Control Settings 5.2.3Effects of Loading Figure 5.10 Effects of Loading 5.2.4Register Change Summary Table 5.1 Register Change Summary for Experiment REGISTER DEFAULT 5.3.1Fan Control Parameters Figure 5.11 Fan Control Parameters 5.3.2Getting Started 5.3.3Forced Kick Function Figure 5.12 Forced Kick Function 5.3.4Spin-UpLevel Figure 5.13 60% Spin Level Setting 5.3.5Spin-UpTime Figure 5.14 Reduced Spin-upTime 5.3.6Register Change Summary Table 5.2 Register Change Summary for Experiment 5.4.1General Setup 5.4.2Controlling the Ramp Rate Figure 5.15 Default Ramp Rate Figure 5.16 Default Step Size with Different UPDATE Settings Figure 5.17 Default UPDATE with Different Step Size Settings Figure 5.18 Exceptionally Slow Rate 5.4.3Register Change Summary Table 5.3 Register Change Summary for Experiment 5.5.1General Setup 5.5.2Fan Configuration Register (52h) Figure 5.19 Update Time Modifications 5.5.3FAN Minimum Drive Register (55h) and Valid TACH Count (56h) Figure 5.20 Minimum Drive Setting Figure 5.21 Valid Tach Count Setting 5.5.4Register Change Summary Table 5.4 Register Change Summary for Experiment 5.6.1General Setup 5.6.2Fan Spin and Stall Interrupts Figure 5.22 Fan Spin and Stall 5.6.3Register Change Summary 5.7.1.1Case 1 - Spin-upLvel RPM < Valid RPM < Target RPM Figure 5.24 Theoretical Plot of Case Figure 5.25 Spin-upCase 1 Fix 5.7.1.2Case 2 - Valid RPM << Target RPM < Spin-upLevel RPM 5.7.1.3Case 3 - Valid RPM =< Target RPM << Spin-upLevel RPM Figure 5.30 Spin-upCase Figure 5.31 Spin-upRoutine Restarted During Normal Operation 5.7.1.4Case 4 - 4.Valid RPM < Spin-upLevel RPM (rpm60 or rpm75) < Target RPM 5.7.1.5Case 5 - Correct RPM Relationships with a Slow Response DC Fan Figure 6.1 A Typical 2-poleDC Fan Figure 6.2 Output Signal of a 2-poleFan Figure 6.3 Fan TACH Measurement With EMC2102 [1] 6.2.1General Setup 6.2.2Set the Correct LIMIT2K Value 6.2.3Determine the Number of Poles and the Maximum Fan Speed 6.2.4Determine the Minimum Startup Speed 6.2.5Determine the Stall Speed 6.2.6Determine the Minimum Valid TACH Speed 6.2.8.1Spin-upLEVEL (Register 53h[2]) 6.2.8.2Minimum Fan Speed 6.2.8.3Valid TACH Count Speed (Function of Register 56h) 6.2.8.4Maximum Fan Speed