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參數(shù)資料
| 型號： | G760A |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Fan Speed PWM Controller |
| 中文描述： | 風(fēng)扇轉(zhuǎn)速PWM控制器 |
| 文件頁數(shù)： | 3/5頁 |
| 文件大?。?/td> | 173K |
| 代理商： | G760A |
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.
1
2
3
4
5
6
7
8
PIN NAME
OUT
F.G.
ON/OFF
GND
CLK
SMBCLK
SMBDATA
V
CC
PIN FUNCTION
PWM output, connect to fan
FAN pulse Input
ON/OFF control pin, 0V means shutdown
Ground
Clock input for fan speed measurement
SMBus clock line
SMBus data line
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
968
1935
2000
3000
4000
5000
6000
7000
8000
9000
10000
20000
30000
CLK=32768Hz
---
254
246
164
123
98
82
70
61
55
49
25
16
CLK=16384Hz
254
127
123
82
61
49
41
35
31
27
25
12
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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