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Global Mixed-mode Technology Inc.
G760A
Fan Speed PWM Controller
Features
Constant Fan Speed Control PWM control for stable operation Build-in MOSFET switch SMBus interface Internal short-circuit protection On/Off control provided
General Description
G760 is a single chip solution for fan speed control, packaged in a space saving SO-8 package. It connects directly to the fan and performs closed-loop control of the fan speed. The only external component required is a 10F capacitor. It determined the current fan speed based on the fan rotation pulses and an externally supplied clock. It uses pulse width modulation (PWM) method and an on-chip MOSFET to control the fan speed to 2% of the programmed speed. The desired fan speed is programmed via the SMBus. The actual fan speed and fan status can be read via the SMBus. Short-circuit protection is implemented to prevent damages to the fan and this IC itself. An On/Off control pin is also provided.
Applications
Notebook PC Industrial PC LAN Switch Servers Telecom equipment Industrial Control
Ordering Information
PART*
G760A
TEMP. RANGE
0C to +70C
PIN-PACKAGE
8-SOP
Pin configuration
G760A
OUT F.G. ON/OFF GND 1 2 3 4 8 7 6 5 V CC SMBDATA SMBCLKLK CLK
8Pin SOP
Ver 4.3 Oct 28, 2002
TEL: 886-3-5788833 http://www.gmt.com.tw
1
Global Mixed-mode Technology Inc.
Absolute Maximum Ratings
PARAMETER
Supply Voltage Operating Temperature Range Junction Temperature Range Storage Temperature Range Lead Temperature (solding) 10 seconds
G760A
MAXIMUM
-0.3 to +7 0 to +70 0 to +125 -65 to +150 300
SYMBOL
VCC TA TJ TSTG TL
UNITS
V C C C C
Electrical Characteristics (Unless specified: VCC = 5V, TA = 25C)
PARAMETER
Supply voltage Shutdown current MOSFET on resistance Short-circuit current limit Input logic low Input logic high Average Output current FG input Positive-going threshold voltage FG input Negative-going threshold voltage FG input Hysteresis voltage
CONDITIONS
VCC On/Off = 0V
MIN
4.5
TYP
5 2 0.2 0.5
MAX
5.5 5 0.25 0.8
UNITS
V A A V V mA V V V
VIL VIH VCC=5V VCC=5V VCC=5V
2.4 350 1.8 0.7 1.1
Application Circuit
5V 10F 3.3V to 5V
VIN FG ON/OFF 10 F *
1N4148
1 2 3 4
8 7 6 5 32.768KHz
10k 10k
FAN
Diode 1N4148 is optional
Block Diagram
OUT VCC
FG
PW M DUTY LOGIC
FAN
CONTROL LOGIC ON/OFF
SET_CNT
ACT_CNT
CLK
FAN_STA
SMBDATA
SMBus CONTROL LOGIC
SMBCLK
Ver 4.3 Oct 28, 2002
TEL: 886-3-5788833 http://www.gmt.com.tw
2
Global Mixed-mode Technology Inc.
Pin Description
PIN NO.
1 2 3 4 5 6 7 8
G760A
PIN FUNCTION
PIN NAME
OUT F.G. ON/OFF GND CLK SMBCLK SMBDATA VCC
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 actually 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 algorithm, thus, the desired fan speed should be programmed 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
When pin 3 (On/Off) is a logical 1, the fan speed will be controlled according to the setting in the programmed fan speed register. There are two ways to stop the fan, (1)setting pin 3 (On/Off) to 0V, (2) program 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 1F-2F 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.
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
Ver 4.3 Oct 28, 2002
TEL: 886-3-5788833 http://www.gmt.com.tw
3
Global Mixed-mode Technology Inc.
Internal Registers This IC provides 3 SMBus registers. 1.Programmed fan speed register:(SET_CNT,address:00b) This register is a read/write register, it contains the count number of the desired fan speed. Power up default is FFh. 2.Actual fan speed register: (ACT_CNT, address: 01b) This register is read only. It contains the count number of
G760A
the actual fan speed. Power up default is FFh. 3.Fan status register: (FAN_STA , address : 10b) This register is read only. Its bit 0 is set to 1 when the actual fan speed is 20% outside the desired speed. Its bit 1 is set to 1 when fan speed is below 1920 rpm. Power up default is 10b.
SMBus Address
The SMBus address of this chip is fixed to7Ch (01111100b) for write and 7Dh(01111101b) for read. SMBus Timing
SMBCLK
1 9 1 9
SMBDATA
0
1
1
1
1
1
0 R/W
0
0
0
0
0
0
D1
D0
Start by Master
Address Byte
Ack by G760
9 1
Pointer Byte
Ack by G760
9
1
0
1
1
1
1
1
0
R/W
D7
D6
D5
D4
D3
D2
D1
D0
Repeat Start by Master
Address Byte
Ack by G760
Data Byte
No Ack by Master
Stop Cond by Master
(a) Typical Pointer Set Followed by Immediate Read
SMBCLK
1 9 1 9
SMBDATA
0
1
1
1
1
1
0 R/W
D7
D6
D5
D4
D3
D2
D1
D0
Start by Master
Address Byte
Ack by G760
Data Byte
No Ack Stop Cond by Master by Master
(b) Typical 1-Byte Read with Preset Pointer
SMBCLK
1 9 1 9 1 9 9
SMBDATA
0
1
1
1
1
1
0 R/W
0
0
0
0
0
0
D1
D0
0
1
1
1
1
1
0
R/W
D7 D6
D5
D4
D3
D2
D1
D0
Start by Master
Address Byte
Ack by G760
Pointer Byte
Ack by G760
Address Byte
Ack by G760
Data Byte
No Ack by Master
Stop Cond by Master
(a) Typical Pointer Set Followed by Immediate Read
SMBCLK
1 9 1 9 1 9
SMBDATA
Start by Master
0
1
1
1
1
1
0
R/W
0
0
0
0
0
0
D1
D0
D7
D6
D5
D4
D3 D2
D1
D0
Address Byte
Ack by G760
Pointer Byte
Ack by Master
Configuration Byte
Ack by G760
Stop Cond by Master
(b) Register Write
Ver 4.3 Oct 28, 2002 TEL: 886-3-5788833 http://www.gmt.com.tw
4
Global Mixed-mode Technology Inc.
Package Information
C
G760A
E
H
L D 7
(4X)
A2 y B A1
A
e
Note: 1. Package body sizes exclude mold flash and gate burrs 2. Dimension L is measured in gage plane 3. Tolerance 0.10mm unless otherwise specified 4. Controlling dimension is millimeter converted inch dimensions are not necessarily exact. SYMBOL
A A1 A2 B C D E e H L y
MIN.
1.35 0.10 ----0.33 0.19 4.80 3.80 ----5.80 0.40 ----0
DIMENSION IN MM NOM.
1.60 ----1.45 ----------------1.27 -----------------
MAX.
1.75 0.25 ----0.51 0.25 5.00 4.00 ----6.20 1.27 0.10 8
MIN.
0.053 0.004 ----0.013 0.007 0.189 0.150 ----0.228 0.016 ----0
DIMENSION IN INCH NOM.
0.063 ----0.057 ----------------0.050 -----------------
MAX.
0.069 0.010 ----0.020 0.010 0.197 0.157 ----0.244 0.050 0.004 8
Taping Specification
Feed Direction Typical SOP Package Orientation
GMT Inc. does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and GMT Inc. reserves the right at any time without notice to change said circuitry and specifications.
Ver 4.3 Oct 28, 2002
TEL: 886-3-5788833 http://www.gmt.com.tw
5

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