4-Wire Pulse Width Modulation (PWM) Controlled Fans Specification September 2005 Revision 1.
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Contents 1 Introduction ......................................................................................................................... 7 1.1 2 Electrical Specifications ...................................................................................................... 9 2.1 2.2 2.3 2.4 3 Overview................................................................................................................. 7 Fan Requirements...............................................................
Figures Figure 1. Screen Shot of PWM Duty Cycle...................................................................... 11 Figure 2 Minimum Fan Speed Requirements: Start Pulse ............................................... 13 Figure 3 Fan Speed Response to PWM Control Input Signal .......................................... 14 Figure 4 Type A Operation, Minimum RPM, Stay on at Minimum RPM........................... 15 Figure 5 Type B Operation, Stay On at Minimum RPM, Off at 0% RPM..........................
Revision History Revision Number Description Revision Date 1.0 Initial Release Nov 2003 1.1 Corrected Tachometer input signal, added definitions to operating modes Dec 2003 1.2 Corrected Section 2.4 PWM input parameter July 2004 1.
Introduction 1 Introduction 1.1 Overview This specification defines the intended operation of a fan that implements the Pulse Width Modulation (PWM) control signal on the 4-wire fan interface. The introduction of 4 wire PWM controlled fans is a means to reduce the overall system acoustics. The expectation is a 4 wire PWM controlled fan when properly implemented will be significantly quieter than a similar 3 wire fan.
Introduction 8
Electrical Specifications 2 Electrical Specifications 2.1 Fan Requirements 2.1.1 Fan Input Voltage Fan operating voltage shall be within the range 12 V ±5% V. 2.1.2 Current Steady state operation fan current draw (with 12.6 V applied, with fan operating in the free stream condition) shall not exceed 1.5 A. Fan current spike during start-up operation (with 12.6 V applied, with fan operating in the free stream condition) shall be allowed to exceed 1.0 A, up to 2.
Electrical Specifications 2.2 Test Methodology To measure the pull up and current sourced from the fan, power the fan to 13.2V and use a DMM (Digital Muli-meter). To verify the pull up value in the fan, measure the voltage between pin 4 (control) and pin 1 (ground). To verify the current sourced by the fan, measure the current between pin 4 (control) and pin 1 (ground). 2.3 Hardware Monitor Device 2.3.
Electrical Specifications Figure 1. Screen Shot of PWM Duty Cycle Figure 1 shows a PWM output operating at 25.3 kHz with a 77.9% duty cycle output with a fan having a ~ 5V pull up on the PWM signal. A 100% duty cycle would be a constant 5V signal with this fan and Hardware Monitor device. 2.4 Considerations for Motherboard Designers 1. 2. The trace from PWM output to the fan header must not have a pull up or pull down. The pull up is located in the fan hub.
Electrical Specifications 12
Fan Speed Control 3 Fan Speed Control 3.1 Maximum Fan Speed Requirements The maximum fan speed shall be specified for the fan model by the fan vendor and correspond to 100% duty cycle PWM signal input. 3.2 Minimum Fan Speed Requirements The vendor shall specify the minimum RPM and the corresponding PWM duty cycle. This specified minimum RPM shall be 30% of maximum RPM or less. The fan shall be able to start and run at this RPM.
Fan Speed Control 3.3 Fan Speed Response to PWM Control Input Signal The PWM input shall be delivered to the fan through the control signal on Pin 4 (see Section 2.1.4). Fan speed response to this signal shall be a continuous and monotonic function of the duty cycle of the signal, from 100% to the minimum specified RPM. The fan RPM (as a percentage of maximum RPM) should match the PWM duty cycle within ±10%. If no control signal is present the fan shall operate at maximum RPM. See Figure 3.
Fan Speed Control Figure 4 Type A Operation, Minimum RPM, Stay on at Minimum RPM Speed vs. PWM Duty cycle % of full speed 35 The fan stays on at minimum speed for all PW M duty cycle values below the minimum PW M duty cycle 30 25 Example Min. PW M 20 ExampleMin. RPM 15 10 5 0 0 5 10 15 20 25 30 35 PW M Duty Cycle In a Type B implementation the fan will run at minimum RPM for all non-zero PWM duty cycle values less than minimum duty cycle and turn off the motor at 0% PWM duty cycle.
Fan Speed Control Figure 5 Type B Operation, Stay On at Minimum RPM, Off at 0% RPM Speed vs. PWM Duty cycle % of full speed 35 The fan stays on at minimum speed for PWM duty cycle values below the minimum PWM duty cycle, and shuts off at 0% PWM duty cycle 30 25 20 Example Min. PWM Example Min. RPM 15 10 5 0 0 5 10 15 20 25 30 35 PWM Duty Cycle In Type C implementation the fan will stop running when the current provided to the motor windings is insufficient to support commutation.
Fan Speed Control Figure 6 Type C, Operation below Minimum RPM, Min, RPM = Starting RPM Speed vs. PWM Duty cycle Example Min. PW M % of full speed 35 The minimum fan speed specified is also the minimum fan starting speed. The fan may continue to run at speeds below the minimum speed, but will not start at that speed. 30 25 20 15 Example Min.
Fan Speed Control 18
Required Features 4 Required Features 4.1.1 Polarity Protection Fan motor shall have polarity protection. 4.1.2 Rotor Lock Protection Fan rotor shall have lock protection and auto-restart 4.1.3 Wire Length To be specified in individual fan specification based on application 4.1.4 Wire Type Wire type shall meet the following minimum qualifications: UL recognized appliance wiring, style UL1430, rated minimum 105C, 300V, 26 gauge. 4.1.
Required Features 20
Environmental and Reliability 5 Environmental and Reliability 5.1.1 Operating Temperature Fan shall be capable of sustaining normal operation over an ambient inlet temperature range of 0°C to 70 °C. 5.1.2 Non-operating Humidity Fan shall be capable of sustaining normal operation at +55 °C / 85 %R.H. 5.1.3 Non-operating Thermal Cycling Fan shall be capable of sustaining normal operation after being subjected to -5 °C to +70 °C for 1000 cycles; ramp = 20 °C/min; 10 min dwell. 5.1.
Environmental and Reliability 22
Reference Drawings 6 Reference Drawings The following pages contain reference drawings for the Connector Housing, and Baseboard Connector.
Reference Drawings Figure 7 Connector Housing 24
Reference Drawings Figure 8 Baseboard Connector 25
