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The first is Dallas MAX6616 resolution in the available fan speed values. The ear-brain system is readily able to recognize small changes in sound pressure level SPL.


If the fan is very quiet, a small number of speed steps on the order of 8 to 10 may be sufficient. When the fan is louder, many times that number approximately 50 to or more may be necessary to Dallas MAX6616 the audibility of speed changes. The second requirement is a mechanism that limits the rate of fan speed change to a specific time period per speed-control increment.

MAX6615 Dual-Channel Temperature Monitors and Fan-Speed Controller with Thermistor Inputs

Monitoring Dallas MAX6616 Speed The most obvious approach to monitoring fan speed is to count the number of tachometer pulses occurring during a fixed period of time, as shown in Figure 26a. This works well if it is possible to count a suitably large number of pulses during a sufficiently short period of time.

As an example, a RPM fan that produces two pulses per revolution will generate a Hz tachometer signal when operating at full speed. If we need to measure and update fan speed once per second, we will be able to count only 50 pulses when the fan is spinning at half speed. This may give enough resolution to determine that the fan is operating, but not enough for precision fan speed control. The most widely used approach is for the fan controller to generate a reference clock, generally in the range of a few kHz, and count the number of clock cycles that occur during Dallas MAX6616 fixed number of tachometer periods usually 1, 2, or 4as shown in Figure 26b.

This allows a tachometer count to be completed in a few milliseconds, so the approach is compatible with closed-loop fan speed control.

Some fan controller ICs include a feature that allows Dallas MAX6616 monitoring of 2-wire fans. While the fan motor operates, its supply current variations create voltage drops on the sense resistor that are compared against a reference voltage by the fan controller IC. This technique has its limitations—supply current waveforms differ significantly from fan to fan, and also vary as fan speed changes, as shown in Figure Therefore, supply current monitoring is more appropriate for detection of fan failure than for closed-loop fan speed control. Examples of fan supply current waveforms. The approach is appropriate for linear drive and PWM power supply drive either high side or low side.

As mentioned briefly in the Controlling Fan Speed section, a complication arises when a fan is driven by a pulse-width modulated power supply. As an example, consider a RPM fan with two Dallas MAX6616 pulses per revolution. This will result in a tachometer frequency of 40Hz, or a tachometer period of 25ms. Note that a much faster fan would work better.

For example, a RPM fan would generate a tachometer signal with a Dallas MAX6616 of 6. This approach works, but its suitability depends on the fan being used. If the pulse needs to Dallas MAX6616 stretched significantly, the pulse stretching will be audible.


Audibility of the pulse stretching depends on the degree of stretching and also on the response time of the fan. Dallas MAX6616 the fan responds quickly to supply voltage changes, the pulse stretching will be easy to hear. A diode provides 4.

MAX Evaluation Kit/Evaluation System - PDF

A disadvantage of this circuit is that the fan is always powered. If necessary, this can be fixed by gating the 5V supply off when the fan needs to Dallas MAX6616 off. The actual fan speed may vary from the nominal value by several percent due to fan-to-fan variations, power supply tolerance, and other uncertainties. Since fan control is usually based on temperature, it makes sense in many systems for the fan controller to be able to measure temperature.

  • MAX6616 Evaluation Kit/Evaluation System
  • Central Office Exchange NXX-208-569 Boise
  • MAX6610 Datasheet (data sheet) PDF

Exceptions include systems where the fan controller is in a location that is physically separate from the temperatures of interest. Closed-Loop, Temperature-Based Thermal Closed-Loop Fan Speed Control Most fan controllers that have temperature-sensing capability are also able to control fan speed based on the measured temperature. The details can vary—most such fan controllers use some sort of straight-line mapping between Dallas MAX6616 and fan drive, while others have a lookup table that associates a few temperature values with fan drive levels. Still others map temperatures to fan RPM values.

MAX6613 Datasheet (data sheet) PDF

Additional features of these fan control devices are shown in Table 5. Table 5.


Simplified examples of discrete circuits were shown in Figures 1, 6, and 10 for interfacing Dallas MAX6616 sensors. Also available are integrated solutions that can simplify the design of these interface circuits Dallas MAX6616 reduce cost. Thermistor resistance vs. The MAX data sheet includes a table showing output code vs. For different thermistor-resistor combinations, create a spreadsheet to calculate the output code as a function of temperature. The digital data is serial and read only. As with the MAX, the data sheet includes a table showing how the output code maps to thermistor temperature for a common thermistor type.

برنامه‌نویسان، سیستم‌های توسعه‌یافته بوردها و کیت‌های ارزیابی و مقدماتی

MAX single thermistor-to-digital converter. The outputs are ratiometric to the power supply voltage, which allows them to be digitized by an ADC that uses the supply voltage as its reference. Maxim Dallas MAX6616 two ICs that integrate all of these functions:The MAX EV kit is a fully assembled and tested cir- Dallas MAX6616 board that For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at. The MAX/MAX monitor two temperature chan- nels, either the For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at.

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