CFA633-RDI-KS datasheet(31/88 Pages) CRYSTAIFONTZ

31 / 88 page

Crystalfontz America, Inc.

Data Sheet Release Date 2012/02/21

www.crystalfontz.com

CFA633-RDI-KS LCD Module (Hardware v2.0 / Firmware s2v1)

February 2012

Page 31

FAN CONNECTIONS

The CFA633-RDI-KS supports up to 4 standard “3-pin” cooling fans. The fan connectors are compatible with industry

standard “3-pin” fans.

Figure 13. Four Fan Connectors

The average power delivered to each fan may be set to any level between 0% and 100% through command 17 (0x11):

Set Fan Power (Pg. 45). The power setting controls the PWM duty cycle of a high-performance open-drain FET

connected between the system ground and the GND pin of each fan connector. The PWM frequency is nominally 18 Hz.

The CFA633-RDI-KS can measure the frequency of the fan's tachometer signal, and given the pulses-per-revolution,

calculate the RPM and display it on the LCD or report the information needed to calculate the RPM to the host. If a fan's

power is set to 100%, then the average frequency of each fan's tachometer signal is measured over a 1/8 second (125

ms) period of time. Each fan is measured in sequence, so updated fan speed information is available every 1/2 second

(500 ms) for each fan.

The power to a fan must be on in order for the fan's tachometer signal to be valid. If a fan is configured to report its speed

to the host, the power of the fan will be unconditionally set to 100% at the start of the 1/8 second period of time when the

CFA633-RDI-KS is measuring the frequency of the tachometer signal, overriding the PWM. The CFA633-RDI-KS will

leave the power to the fan on until the glitch delay (see command 26 (0x1A): Set Fan Tachometer Glitch Filter (Pg. 52)

has expired and two tachometer edges have been detected. The normal PWM cycle will then resume.

This technique allows the fan speed to be measured with a very minimal effect on the speed of the fan. If the fan power

is set to 100% or if the speed of the fan and length of the PWM on time are such that the speed can be measured without

stretching the PWM, then this override will not change the speed of the fan at all. If the fan power is set to some level

other than 100% and the PWM on time is short compared to the tachometer signal frequency, then the fan speed will

pulse slightly every 1/2 second due to the stretching of the PWM on time. During tachometer measuring, the maximum

width of a stretched on pulse is 1/8 second. For some fans, the result is not very noticeable, and this technique will allow

you to monitor the average speed of the fan while controlling the average power of the fan. For other fans (particularly

high torque, high RPM models) the pulsing effect may be undesirable.

c 2010

America, Inc.

Crystalfontz

FAN2

FAN1

J_DOW

J_PWR

TACH

GND

PWR

TACH

FAN3

FAN4

PWR

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