Datasheet MAX6665 (Maxim) - 4

Fan Controller/Driver with Factory- Programmed Temperature Thresholds Pin Description PIN NAME FUNCTION
1 GND Ground Force Fan On Input. Set FORCEON low to force the fan switch on. Set FORCEON high for normal 2 FORCEON operation.
MAX6665
Three-State Hysteresis Input. Connect HYST to V 3 HYST DD for 8°C, GND for 4°C, and leave HYST unconnected for 1°C hysteresis. Fan-On Indicator Output. Push-pull output. FANON is high when the fan switch is on. FANON is low 4 FANON when the fan switch is off. Overtemperature Output. Active-low when the temperature is 30°C above the fan threshold. Open- 5 OT drain output, requires resistive pullup. Overtemperature Warning Output. Active-low when the temperature is 15°C above the fan 6 WARN threshold. Open-drain output, requires resistive pullup. 7 VDD Supply Voltage. Bypass with a 1µF capacitor to GND as close to VDD pin as possible. 8 FANOUT Fan-Switch (Driver) Output. Connect to the low side of a fan. Exposed GND Ground Paddle
Detailed Description Applications Information
The MAX6665 is a simple fan controller/driver that turns
Thermal Considerations and Hysteresis
on the internal power transistor when its die tempera- The temperature comparator has hysteresis to prevent ture exceeds a factory-set threshold. By connecting a small temperature changes near the threshold temper- small (typically 5V to 12V, 100mA to 250mA) cooling ature from causing the fan to turn on and off repeatedly fan to FANOUT, a simple on/off fan-control system is over short periods of time. The FANOUT pin goes created. FANOUT drives the fan’s low side. The fan’s active and powers the fan when the MAX6665’s die positive supply pin should be connected to its normal temperature exceeds the factory-programmed trip tem- power-supply voltage (up to 24V nominal). perature. As the cooling fan operates, the circuit board To turn the fan on when the MAX6665’s die temperature temperature should decrease, which in turn causes the is less than the threshold voltage, drive FORCEON low. MAX6665’s die temperature to decrease. When the die This overrides the internal control circuitry and allows temperature is equal to the trip threshold minus the an external device to activate the fan. FANON is an hysteresis, the FANOUT pin turns the fan off, removing active-high push-pull logic output that goes high when power from the fan. The HYST pin sets the amount of the fan is turned on, either when temperature exceeds hysteresis to 1°C, 4°C, or 8°C by letting the pin float or the threshold or the fan is forced on. connecting to GND or VDD, respectively. This allows WARN is an active-low, open-drain digital output that the amount of hysteresis to be matched to the cooling indicates the MAX6665’s die temperature exceeds and noise requirements of the system. 15°C above the fan trip threshold. WARN output serves Hysteresis is also affected by self-heating of the as a warning that the system temperature has contin- MAX6665’s die. The fan current flowing through the on- ued to rise well above the fan activation temperature. chip power transistor causes the die temperature to OT is an active-low open-drain digital output that indi- increase. For example, assume the MAX6665 controls cates the MAX6665’s die temperature exceeds 30°C a 125mA fan. When the fan is operating, the voltage above the fan trip threshold. It serves as a thermal shut- drop across the output transistor is typically under down output to the system in case of excessive temper- 250mV. At 250mV, the power dissipation is 31.25mW. ature rise. Figure 1 shows a typical application circuit The thermal resistance of the MAX6665 package (with for a high-reliability, fail-safe temperature monitor. EP soldered) is 51°C/W, so the die temperature
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