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Dynamic Power linearization to generate fan table

IP.com Disclosure Number: IPCOM000238393D
Publication Date: 2014-Aug-22
Document File: 1 page(s) / 68K

Publishing Venue

The IP.com Prior Art Database

Abstract

In the current cooling algorithm, in order to avoid the overshooting issue, the power ratio table was deployed to change the fan speed slope. However, it is more cooling power wasting if using the table. At this point, more table need to be placed inside the code. A new method is used to generate the fan speed value and there is no need to add the extra table for this power ratio table. It can save more power and avoid the overshooting issue. This idea is to use the linear equation of power and temperature to compute the right cooling fan speed output and there is only one base fan table required in the BMC deployment.

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Dynamic Power linearization to generate fan table

    In this idea, there is a need to find out one base fan. A new method is used to generate the fan speed value and there is no need to add the extra table for this power ratio table. It can save more power and avoid the overshooting issue. First of all, ambient base fan table is the only table to be created. Secondly, the linearized power ratio equation shown below is to be used to output the right PWM value to fan. The key to formulate the equation is to get the right PWM increase according to the linear CPU power increase and get the PWM correlation per CPU power. Once this correlation is found, the fan speed will ramp according to the CPU power jump to achieve the purpose with smooth ramp.

    In the attached picture shown below, pink dash line is the original power band method to avoid the CPU overshoot issue and the step of the fan ramp is obviously seen. However, the blue dash line improves this step issue causing the fan oscillation. From the CPU thermal point of view, the CPU temperature can be steadily maintained below the required target temperature shown in the light blue dash line.

PWM = Ambient_Base_PWM + ( Power / TDP * 100 - 50 )

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