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National Semiconductor Thermal Management Product Provides Design Flexibility for Fan Control Applications in Notebook and Desktop Computers
| The manufacturer says . . . | ChipCenter's Paul O'Shea says . . . |
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National Semiconductor Corporation announced the LM63, a +/- 1 degree C accuracy remote diode temperature sensor with integrated fan control. The pulse width modulated (PWM) signal output of Nationalıs LM63 controls the fan speed based on the temperature of the remote diode sensor. The flexibility in fan control programming in this device enables the same design to be used with different fans and processors, which will reduce design cost for systems providers. ıNational Semiconductor has one of the industry's broadest portfolios of thermal management products, and to continue this trend, we are adding products with integrated fan control, like the LM63, to our portfolio, ı said Zaryab Hamavand, marketing manager for Nationalıs thermal solutions products. ıAs a leader in temperature sensor innovation, National continues to drive the market by developing products with the highest accuracy, lowest power and smallest packaging in the industry.ı Nationalıs LM63 is targeted for applications in PC notebooks, desktops, workstations, servers, and other CPU-based systems such as Thin Clients. It can also be used in base stations, routers, fan modules, or any system that requires fan control based on the temperatures. The LM63 has a local and remote diode temperature sensor, which senses the temperature of an integrated diode in a target IC, such as a Pentium III or IV processor, or a discrete transistor, such as 2N3904, and its own location. It has +/-1 degree C accuracy including the quantization error and features a programmable PWM output, which controls the fan speed based on the remote diode temperature. This device also has an 8-step look-up table, which can be programmed to create a non-linear transfer function fan control based on the temperature. This allows designers to avoid the resonant frequency of the fan and achieve better acoustic performance in their systems. This product contains a fan tachometer-monitoring system that monitors the fan tachometer correctly when the fan voltage is modulated by either low- or high-frequency PWM output. The LM63 also has an offset register, which helps designers maintain accuracy while using CPUs with different non-ideality factors or different trace lengths by simply adjusting the register. The LM63 also incorporates a programmable digital filter to reduce the noise in thermal measurement of integrated diodes.
National Semiconductor |
National has a wide portfolio of thermal management products. The LM63 is the first member of a new family of integrated fan control sensor products. It provides the performance for temperature accuracy and reduces acoustic noise. The remote diode sensor works with the processorıs integrated diode, which varies according to temperature when current passes through it. Based on the voltage the LM63 calculates the temperature of the diode. For example, many CPU manufacturers like Intel and AMD have an integrated diode for the single purpose of monitoring the temperature. The LM63 has a diode sensor and builds on that by integrating the fan control. The fan control has flexibility, and is used for PCs of all types and can be integrated into fan modules. The LM63 also has a temperature sensor allowing users to monitor the location of the temperature and control the fan. It varies the fan speed according to the temperature and does it automatically. You may wonder why is it important to have a fan speed that varies as opposed to just on and off. One reason is noise; if you have the fan on the maximum speed itıs noisy. The second reason is that fan speed control can increase the battery life, which is important for notebook computers. The LM63 can work with all processors and doesnıt have to be placed on the processor because it can use the 2N9304 transistor that connects to the LM63 via two pins. The LM63 monitors the temperature of the transistor, which can be located in the hot spot. The transistor can also be used with integrated diodes on CPUs like those from Intel and AMD or with FPGAs, and graphic processors. Another important aspect of this part is the 8-step look up table. Typically, the fan control is linear. That means you set the starting point of the temperature where the fan will run at 100%. National provides the user with 8 steps based on the temperature, so at a particular temperature it helps provide the pulse width modulation (PWM) that you require for that temperature. Additionally, because of hysteresis, when you move to the step above your present step it will take longer than it will take to go down a step providing a non-linear fan control based on temperature. For example, if the room temperature is on the Y-axis and the PWM is on the X-axis, the fan control will be displayed as a step function. Another feature of the LM63 is the flexibility provided when the fan is turned on, and inertia has to be overcome. Typically, the fan must go 50% to 100% of the duty cycle for a specified duration to make sure the fan is started. National enables you to program this duration and duty cycle. Another aspect of this part is that it can be used with different fans. Every fan has a resonant frequency. At the resonant frequency the fan is noisy. In linear fan control you canıt avoid the resonant frequency. In this design, you program the profile that you want the fan to use to avoid the resonant frequency. You avoid the resonant frequency when you program the frequency and PWM of the fan. It means you have to know the resonant frequency, but most fan manufacturers provide that information. Unlike other fan controls that work only on a low frequency PWM, typically below the audible range, the LM63 allows you to program the fan below or above audible frequency. Thatıs just one more instance of flexibility offered by National for designing your fan control. The LM63 also provides offset registers to compensate for the non-ideality factor of the CPU. Non-ideality is the change in how the processor interacts with the diode. It is the variance in the diode characteristics due to a different processor. That factor will cause errors in the temperature readings of the diode. The designer can change the offset registers to compensate for the differences in the parts. Additionally, the offset register can help compensate for trace lengths. Both of these help the designer maintain accuracy when they make changes in the design due to the processor or the trace lengths. You may change the CPU or the location of the CPU. Or you may even change the location of the external transistor. The off-set register can help compensate for these changes. Finally, a digital smoothing filter helps reduce the sensitivity of the readout to noise. It controls spikes from the CPU. The digital filter will help prevent dramatic fan speed differences due to these temperature spikes. The LM63 is sampling now in SO-8 packaging and is priced at $2.10 in 1000-unit quantities.
Nationalıs temperature sensor products
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