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SMSC EMC2102 USER MANUAL, 5.4.1General Setup, Figure 5.15 Default Ramp Rate, 5.4.2Controlling the Ramp Rate

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Fan Speed Control with the EMC2102 Device

5.4Experiment 4 - RPM Drive Mode Rate Controls

This experiment is designed to gain familiarity with the rate control options available in the EMC2102 devices.

This experiment will discuss the effects of Maximum Fan Step and Update rate that can be used to control the ramp rate of a fan. The two parameters ensure the fan reaches the desired drive in a reasonable time with no oscillations.

The CMF file for this experiment is the same as for Experiment 1, EMC1202_default.cmf.

5.4.1General Setup

For all these tests, the Fan Drive Setting register (51h) and the TACH Reading registers (58h) are selected to plot. As bits are switched in each of the tests, the register name and address will be provided.

5.4.2Controlling the Ramp Rate

Controlling the ramp rate can improve the performance of the fan control loop by limiting the slew rate of the fan drive. The EMC2102 uses the UPDATE bits in the FAN Configuration register (52h, bits [2:0]) to determine the time interval between two updates of the controller output, and uses the FAN Step register (54h) to determine the maximum allowed hexadecimal count (STEP) of the output (Refer to Figure 5.11 "Fan Control Parameters" for more details). These two parameters can only work in the RPM control mode. When the RPM control function is disabled (52h[7]= 0), any change in the Fan Drive Setting register (51h) will immediately change the output.

The plots in Figure 5.15, "Default Ramp Rate" illustrate the drive and response with the default UPDATE (400ms) and default STEP SIZE (Max. 16 drive settings per update), while changing the fan target speed from 4000 rpm to 6000rpm.

Figure 5.15 Default Ramp Rate

The ramping rate in this mode can be accelerated or slowed down, depending on application and the values of register 52h (UPDATE) and 54h (STEP SIZE). In the next experiment (Figure 5.16, "Default Step Size with Different UPDATE Settings"), the default STEP SIZE with different UPDATE (400 ms and 100 ms) were used, The 100 ms setting has the effect of speeding the loop up by a factor of 4, as that is the ratio between minimum (100ms) and default (400ms) UPDATE settings.

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