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© 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
Remote
Sensor
Remote
Sensor
CPU
NDT3055L
or FDC637AN
SMBDAT
SMBCLK
2.2K
2.2K
10K
5V
3.3V
5V 3-Wire Fan
in Cooling
Module
aSC7512
VDD
D +
D -
PWM
GND
TACH
SMBDAT
SMBCLK
6
8
7
5
3
1
2
4
Remote
Sensor
CPU
SMBDAT
SMBCLK
2.2K
2.2K
10K
5V
12V
4-Wire Fan
in Cooling
Module
aSC7512
VDD
D +
D -
PWM
GND
TACH
SMBDAT
SMBCLK
3
1
2
4
CPU
NDT3055L
or FDC637AN
SMBDAT
SMBCLK
2.2K
2.2K
10K
5V
3.3V
5V 2-Wire Fan
in Cooling
Module
aSC7512
VDD
D +
D -
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
Sensor
Remote
Sensor
CPU
NDT3055L
or FDC637AN
SMBDAT
SMBCLK
2.2K
2.2K
10K
5V
3.3V
5V 3-Wire Fan
in Cooling
Module
aSC7512
VDD
D +
D -
PWM
GND
TACH
SMBDAT
SMBCLK
6
8
7
5
6
8
7
5
3
1
2
4
3
1
2
4
Remote
Sensor
CPU
SMBDAT
SMBCLK
2.2K
2.2K
10K
5V
12V
4-Wire Fan
in Cooling
Module
aSC7512
VDD
D +
D -
PWM
GND
TACH
SMBDAT
SMBCLK
3
1
2
4
3
1
2
4
CPU
NDT3055L
or FDC637AN
SMBDAT
SMBCLK
2.2K
2.2K
10K
5V
3.3V
5V 2-Wire Fan
in Cooling
Module
aSC7512
VDD
D +
D -
PWM
GND
TACH
SMBDAT
SMBCLK
6
8
7
5
6
8
7
5
3
1
2
4
6
8
7
5
6
8
7
5
10K
15K
7.5K
10K
10K
3.3V
3.3V
Optional
ALERT
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