
- 32 - 
 Andigilog, Inc. 2006 
www.andigilog.com
August 2006 - 70A05003 
aSC7512
Thermal Considerations 
The temperature of the aSC7512 will be close to that of 
the PC board on which it is mounted. Conduction through 
the leads is the primary path for heat flow. The reported 
local sensor is very close to the circuit board temperature 
and typically between the board and ambient. 
In order to measure PC board temperature in an area of 
interest, such as the area around the CPU where voltage 
regulator components generate significant heat, a remote 
diode-connected transistor should be used. A surface-
mount SOT-23 or SOT-223 is recommended. The small 
size is advantageous in minimizing response time 
because of its low thermal mass, but at the same time it 
has low surface area and a high thermal resistance to 
ambient air. A compromise must be achieved between 
minimizing thermal mass and increasing the surface area 
to lower the junction-to-ambient thermal resistance. 
In order to sense temperature of air-flows near board-
mounted heat sources, such as memory modules, the 
sensor should be mounted above the PC board. A TO-92 
packaged transistor is recommended. 
 The power consumption of the aSC7512 is relatively low 
and should have little self-heating effect on the local 
sensor reading. At the highest measurement rate the 
dissipation is less than 2mW, resulting in only a few 
tenths of a degree rise. 
Evaluation Board 
The aSC7511/aSC7512EVB provides a platform for 
evaluation of the operational characteristics of the 
aSC7511 and aSC7512.  The board features a graphical 
user interface (GUI) to control and monitor all activities 
and readings of the aSC7511. The provided software will 
run on a Windows XP-based desktop or laptop PC with 
a USB port. 
In addition to being a self-contained fan speed control 
demonstration, it may be connected into an operating 
PC’s fan and CPU diode to evaluate various settings 
under real operating conditions without the need to adjust 
BIOS code. After optimization, the settings may be 
programmed into the system. 
Features: 
Interactive GUI for setting limits and operational 
configuration 
aSC7512 Automatic Fan Control 
Powered and operated from the USB port 
Graphical readouts: 
Temperature and alarms 
Fan RPM 
Automatic fan control state 
Selectable on-board 2N3904 or wired remote 
diode 
Headers for 2-, 3- and 4-wire fans 
Customizable Log file of readings 
Saving of register setting configurations 
LED indicator of pin state 
Optional use of external 12V fan power for 
higher current fans 
Optional connection to off-board SMBus clients 
Application Diagrams 
The aSC7512 may be easily adapted to two-, three- or 4-
wire fans for precise, wider-range fan speed control when 
compared to variable DC drive. Pin 6 may optionally be 
used as 
ALERT
 , pulled up to 3.3V with a 10K resistor to 
warn the system of an extreme condition needing 
immediate attention in any fan configuration. 
Figure 14 aSC7512  2-, 3- and 4-Wire Fan 
Connections
Sensor
Sensor
CPU
or FDC637AN
SMBDAT
SMBCLK
2.2K
2.2K
10K
5V
3.3V
Module
D -
VDD
aSC7512
PWM
GND
TACH
SMBDAT
SMBCLK
6
8
7
5
3
1
2
4
Sensor
CPU
SMBDAT
SMBCLK
2.2K
2.2K
10K
5V
12V
Module
D -
VDD
aSC7512
PWM
GND
TACH
SMBDAT
SMBCLK
3
1
2
4
CPU
or FDC637AN
SMBDAT
SMBCLK
2.2K
2.2K
10K
5V
3.3V
Module
D -
VDD
aSC7512
PWM
GND
TACH
SMBDAT
SMBCLK
6
8
7
5
3
1
2
4
6
8
7
5
10K
15K
7.5K
10K
3.3V
3.3V
Remote
Remote
NDT3055L 
5V
in Cooling
D +
Remote
in Cooling
D +
NDT3055L 
5V
in Cooling
D +
Optional 
ALERT