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P82CF201BDH Datasheet(PDF) 5 Page - NXP Semiconductors |
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P82CF201BDH Datasheet(HTML) 5 Page - NXP Semiconductors |
5 / 11 page Philips Semiconductors Product data P82CF201 Low power, low price dual fan manager 2002 Nov 18 5 Motor Failure Detection and fault Reporting (including watchdog reset) As shown in Figure 4, the VSENSE input is connected to the collector of NPN transistor through an inverting buffer transistor (2N3904 or PMBT3904D) which amplifies the signal from the low-value current sensing resistor in the ground return leg of the fan circuit. During normal fan operation, communication occurs as each pole of the fan is energized. The fan current develops across the sense resistor(RSENSE). This a voltage follower of the PWM pin. In a running motor, a current will flow through the resistor RSENSE resulting in a voltage drop. The commutation will cause a narrow window where there is no current flow. Motor detection is done by the presence of commutation pulses. If there is constant voltage level on the VSENSE pin when the motor is driven by a PWM signal, the motor is jammed. When there is no voltage at all, the motor might not be connected or the MOSFET is defective. The fault condition also triggers the maximum PWM applied to the running fan. To detect the commutation pulses correctly, the VSENSE input needs a logic high level of 0.2*VDD+0.9 V. (For example: 1.56 V@VDD=3.3 V). The design of proper sense circuitry is a matter of scaling the RSENSE and the gain in buffer transistor to meet the logic high as shown in Figure 4. Assuming the VBE(min) of the transistor is approx. 0.5 V. Table 1 lists some recommended RSENSE values according to the nominal operating current. Table 1. Recommended values of RSENSE per Figure 4 Nominal Fan Current(mA) Min RSENSE(ohms) 100 5.1 200 2.5 450 2.2 800 1.0 In addition, when the thermistor resistance falls below 1.7 K Ω (for NTC thermistor) indicating temperature above 76 °C, the fault line will be asserted. When the fan fails continuously, the fault signal will be held on LOW. su01720 FANXDRIVE VSENSEx 3.3 V 12 V FAN +12 V Q1 SI4410DY RSENSE (2.2 Ω TYPICAL) +12 V 3.3 V Figure 4. Interfacing the 82CF201 to a 2-Wire fan. |
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