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MAX6639 Datasheet(PDF) 18 Page - Maxim Integrated Products |
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MAX6639 Datasheet(HTML) 18 Page - Maxim Integrated Products |
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18 / 22 page  Quick-Start Guide for 8000RPM 4-Pole (2 Pulses per Revolution) Fan in Automatic RPM Mode Using the Circuit of Figure 7 1) Write 02h to register 11h to set the PWM output to drive the n-channel MOSFET. 2) Write 4Bh to register 22h to set the minimum RPM to 3200. 3) Write 5Eh to register 24h to set the pulses per revo- lution to 2 and to set the maximum RPM speed to 8000RPM. 4) Write 19h to register 28h to set the fan-start temper- ature to +25°C. 5) Write D2h to register 10h to start automatic RPM mode. Remote-Diode Considerations Temperature accuracy depends upon having a good- quality, diode-connected, small-signal transistor. Accuracy has been experimentally verified for all the devices listed in Table 12. The MAX6639 can also directly measure the die temperature of CPUs and other ICs with on-board temperature-sensing diodes. The transistor must be a small-signal type with a rela- tively high forward voltage. This ensures that the input voltage is within the A/D input voltage range. The for- ward voltage must be greater than 0.25V at 10µA at the highest expected temperature. The forward voltage must be less than 0.95V at 100µA at the lowest expect- ed temperature. The base resistance has to be less than 100 Ω. Tight specification of forward-current gain (+50 to +150, for example) indicates that the manufac- turer has good process control and that the devices have consistent characteristics. Effect of Ideality Factor The accuracy of the remote temperature measurements depends on the ideality factor (n) of the remote diode (actually a transistor). The MAX6639 is optimized for n = 1.008, which is the typical value for the Intel® Pentium® III and the AMD Athlon MP model 6. If a sense transistor with a different ideality factor is used, the output data is different. Fortunately, the difference is predictable. Assume a remote-diode sensor designed for a nominal ideality factor nNOMINAL is used to measure the tem- perature of a diode with a different ideality factor, n1. The measured temperature TM can be corrected using: where temperature is measured in Kelvin. As mentioned above, the nominal ideality factor of the MAX6639 is 1.008. As an example, assume the MAX6639 is configured with a CPU that has an ideality factor of 1.002. If the diode has no series resistance, the measured data is related to the real temperature as follows: For a real temperature of +85°C (358.15K), the mea- sured temperature is +82.91°C (356.02K), which is an error of -2.13°C. TT n n TT ACTUAL M NOMINAL MM = ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ = ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ = 1 1 008 1 002 1 00599 . . (. ) TT n n M ACTUAL NOMINAL = ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ 1 2-Channel Temperature Monitor with Dual, Automatic, PWM Fan-Speed Controller 18 ______________________________________________________________________________________ FIGURE DESCRIPTION PULSE STRETCHING PWM FREQUENCY PWM POLARITY 6 High-side PWM drive Yes Low Negative 7 Low-side PWM drive Yes Low Positive 8 High-side PWM drive with keep-alive supply No Low Negative 9 High-side linear supply No High Positive 10 4-wire fan with PWM speed-control input No High Positive Table 11. Summary of Fan-Drive Options MANUFACTURER MODEL NO. Central Semiconductor (USA) CMPT3906 Rohm Semiconductor (USA) SST3906 Samsung (Korea) KST3906-TF Siemens (Germany) SMBT3906 Table 12. Remote-Sensor Transistor Manufacturers Intel and Pentium are registered trademarks of Intel Corp. |
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