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G760A Datasheet(PDF) 3 Page - List of Unclassifed Manufacturers |
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G760A Datasheet(HTML) 3 Page - List of Unclassifed Manufacturers |
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3 / 5 page  Ver 4.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw 3 G760A Global Mixed-mode Technology Inc. Pin Description PIN NO. PIN NAME PIN FUNCTION 1 OUT PWM output, connect to fan 2 F.G. FAN pulse Input 3 ON/OFF ON/OFF control pin, 0V means shutdown 4 GND Ground 5 CLK Clock input for fan speed measurement 6 SMBCLK SMBus clock line 7 SMBDATA SMBus data line 8 VCC Supply voltage Description The fan speed is measured by counting the number of the CLK pin period between the rising edges of two fan speed pulses on FG pin. In this way, we are actu- ally measuring the period of the fan speed. To avoid the cost of doing division to obtain the speed, this count number, N, is used in the PWM control algo- rithm, thus, the desired fan speed should be pro- grammed by writing the corresponding count number. The count number is given by: N = (CLK x 30) / (rpm x P) N : Count Number P : FG pulses number per revolution of fan. For CLK = 32768Hz, P = 2 ⇒N = 491520 / rpm For CLK = 16384Hz, P = 2 ⇒N = 245762 / rpm Some selected count numbers are shown below Table 1. Count numbers for P=2 rpm CLK=32768Hz CLK=16384Hz 968 --- 254 1935 254 127 2000 246 123 3000 164 82 4000 123 61 5000 98 49 6000 82 41 7000 70 35 8000 61 31 9000 55 27 10000 49 25 20000 25 12 30000 16 8 When pin 3 (On/Off) is a logical 1, the fan speed will be controlled according to the setting in the pro- grammed fan speed register. There are two ways to stop the fan, (1)setting pin 3 (On/Off) to 0V, (2) pro- gram the fan speed register to 255. These also makes the fan controller into power saving mode. Controlling Fan at Lower Speed For stably controlling fans at lower rotation speed, three schemes are recommended as below: 1.Use larger decoupling capacitors between FAN_OUT and GND. 2.Shunt a capacitor of 1µF-2µF on FG pin to GND. 3.Use fans with open-collector FG outputs. When controlling fans under lower rotation speed, the output voltage of FAN_OUT would be too low for fan to generate recognizable FG signals. Using decouple capacitors on FAN_OUT and FG is to increase the SNR on FG pins. While using fans with open_collector FG outputs can thoroughly solve the problem, because the logic high level of FG would be fixed to 5V. |
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