The AMC6821 is an intelligent temperature monitor and pulse-width modulation (PWM) fan controller. It is designed for noise-sensitive or power-sensitive applications that require active system cooling. Using either a low-frequency or a high-frequency PWM signal, this device can simultaneously drive a fan, monitor remote sensor diode temperatures, and measure and control the fan speed so that it operates with minimal acoustic noise at the lowest possible speed.
The AMC6821 has three fan control modes: Auto Temperature-Fan mode, Software-RPM mode, and Software-DCY mode. Each mode controls the fan speed by changing the duty cycle of a PWM output. Auto Temperature-Fan mode is an intelligent, closed-loop control that optimizes fan speed according to user-defined parameters. This mode allows the AMC6821 to run as a stand-alone device without CPU intervention; the fan can continue to be controlled (based on temperature measurements) even if the CPU or system locks up. Software-RPM mode is a second closed-loop control. In this mode, the AMC6821 adjusts the PWM output to maintain a consistent fan speed at a user-specified target value; that is, the device functions as a fan speed regulator. Software-RPM mode can also be used to allow the AMC6821 to operate as a stand-alone device. The third mode, Software-DCY, is open-loop. In Software-DCY mode, the PWM duty cycle is set directly by the value written to the device.
The AMC6821 has a programmable SMBALERT output to indicate error conditions and a dedicated FAN-FAULT output to indicate fan failure. The THERM pin is a fail-safe output for over-temperature conditions that can be used to throttle a CPU clock. Additionally, the OVR pin indicates the over-temperature limit as well. All of the alarm thresholds are set through the device registers. The AMC6821 is available in a QSOP-16 package.
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