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SMSC EMC2102 USER MANUAL, Figure 5.20 Minimum Drive Setting, Figure 5.21 Valid Tach Count Setting, 5.5.3FAN Minimum Drive Register (55h) and Valid TACH Count (56h)

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Fan Speed Control with the EMC2102 Device

5.5.3FAN Minimum Drive Register (55h) and Valid TACH Count (56h)

These two registers assist the user in defining the operational environment for a given fan. The Minimum Drive register is an absolute minimum value the RPM controller may drive to in an attempt to achieve low RPM settings. The Valid Tach Count register is used to compare against the Tach Target register. No value less than the Valid Tach Count will be accepted by the controller. To examine this feature, set the minimum drive to C0h, and command an RPM setting of less than 5500 RPM. The fan will start at about 5600 rpm (51h = C0h). Set the target to 6000 rpm, and the fan speed follows. Drop the fan target speed from 6000 rpm to 4500 rpm, the real fan speed will only drop to about 5560 rpm, as shown in Figure 5.20, "Minimum Drive Setting".

Fan starts at

Minimum Drive

Fan will not run below

Minimum Drtive

Figure 5.20 Minimum Drive Setting

Likewise, the Valid TACH Count register operation is simple to show. Start the fan at 6000 RPM with all default setting, and then set the Valid TACH register to 5000 RPM. Enter a command of 4800 RPM, and the fan will not respond as shown in Figure 5.21, "Valid Tach Count Setting".

Target of 4800 rpm

Figure 5.21 Valid Tach Count Setting

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