4-Wire Pulse Width Modulation (PWM) Controlled Fans Specification

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 2.2A maximum for a duration of no

greater than 1.0 sec.

2.1.3 Tachometer Output Signal

Fan shall provide tachometer output signal with the following characteristics:

• Two pulses per revolution

• Open-collector or open-drain type output

• Motherboard will have a pull up to 12V, maximum 12.6V

2.1.4 PWM Control Input Signal

The following requirements are measured at the PWM (control) pin of the fan cable connector see

Figure 7 and Table 1:

PWM Frequency: Target frequency 25 kHz, acceptable operational range 21 kHz to 28 kHz

Maximum voltage for logic low: VIL = 0.8 V

Absolute maximum current sourced: Imax = 5 mA (short circuit current)

Absolute maximum voltage level: VMax = 5.25 V (open circuit voltage)

This signal must be pulled up to a maximum of 5.25V within the fan.

Note: New fan designs are strongly encouraged to implement a 3.3V pull up for compatibility with

buffer design limits on Hardware Monitor Devices e.g. Super IO devices.