Standard Microsystems Corporation

Leonid A Bekker

Scott Cameron McLeod

Steven Burstein

Thomas R Anderson

Robert W Schoepflin

Uri Segal

System and method for controlling a fan. A value may be received for controlling the fan. The value may include a first number of bits and may correspond to a linear function of temperature. A first value may be determined using a first number of bits of the value. A modification to the first value may be determined based on a second number of bits of the value. A new output value may be generated based on the first value and the modification to the first value. The new output value may correspond to a first nonlinear function of temperature. The new output value may be provided for controlling the fan.

Generating a nonlinear function for fan control

A temperature sensor circuit and system providing accurate readings using a temperature diode whose ideality factor may fall within a determined range. In one set of embodiments a change in diode junction voltage (&#x394;V) proportional to the temperature of the diode is captured and provided to an ADC, which may perform required signal conditioning functions on &#x394;V, and provide a numeric value output corresponding to the temperature of the diode. Errors in the measured temperature that might result from using diodes with ideality factors that differ from an expected ideality factor may be eliminated by programming the system to account for differing ideality factors. The gain of the temperature sensor may be matched to the ideality factor of the temperature diode by using an accurate, highly temperature stable reference voltage of the ADC to set the gain of the temperature measurement system. The reference voltage may have a trim capability to change the gain setting voltage by a digital address comprising a determined number of bits, with the programmable range for the reference voltage corresponding to a determined range of ideality factors.

Programmable ideality factor compensation in temperature sensors

A system and method for measuring the speed of a fan is presented. The duty cycle of a pulse width modulated (PWM) power signal may control speed of the fan. The fan may generate tachometer pulses used for monitoring RPM of the fan. Very low frequency test pulses may be generated and provided via a test signal multiplexed with the PWM signal to obtain tachometer pulses present even when the PWM signal is deasserted. The frequency of the test signal may be determined based on the duty cycle of the PWM signal and may be dynamically updated using frequency divider values stored in a user programmable look-up table. The tachometer pulses may be used to reset a flip-flop whose data input is held high and a down counter, which may be operated at a frequency slightly lower than the frequency of the test signal, with the output of the down counter clocking the flip-flop. The output of the flip-flop may provide recreated tachometer pulses to a pulse counter that counts the number of pulses within a determined period of time, providing a measured RPM of the fan.

Method and apparatus to achieve accurate fan tachometer with programmable look-up table

A system and method for generating a test signal used in measuring the speed of a rotating device, such as a fan in a computer system is disclosed. A pulse width modulated (PWM) signal may power the fan with the duty cycle of the PWM signal controlling the speed of the fan. The fan may generate tachometer pulses used for monitoring RPM of the fan. The frequency of the test signal may be selected to be at least twice the frequency of the tachometer pulses. The test signal may be generated from a base frequency signal using two cascaded frequency dividers. The first divider may output a scaled base frequency signal obtained by dividing the base frequency signal by a user programmable scale frequency coefficient corresponding to a maximum test signal frequency for the fan. The second divider may output the test signal by dividing the scaled base frequency signal by a fraction frequency coefficient obtained from and proportional to the current PWM duty cycle value. The test signal may be multiplexed with the PWM signal to obtain existing tachometer pulses even when the PWM signal is not asserted. The scale frequency coefficient may only need to be programmed once for each fan.

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Holbrook, NY, United States of America

Leonid A Bekker