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© Andigilog, Inc. 2006
www.andigilog.com
October 2006 - 70A06010
aSC7621
Pin Descriptions
Symbol
Pin
Type
Name and Function/Connection
SMBDAT
1
Digital I/O
(Open-Drain)
System Management Bus Data. Open-drain output. 5V
tolerant, SMBus 2.0 compliant.
SMBCLK
2
Digital Input
System Management Bus Clock. Tied to Open-drain
output. 5V tolerant, SMBus 2.0 compliant.
PECI
7
Digital I/O
Platform Environmental Control Interface (PECI). PECI 1.0
compliant, CPU digital thermometer input
Vtt
8
Analog Input
PECI reference voltage.
3.3V
4
POWER
+3.3V pin. Can be powered by +3.3V Standby power if
monitoring in low power states is required. This pin should
be bypassed with a 0.1
μF capacitor in parallel with 100pF.
A bulk capacitance of approximately 10
μF needs to be in
near vicinity of the aSC7621.
GND
3
GROUND
Ground for all analog and digital circuitry.
5V
20
Analog Input
Analog Input for +5V monitoring.
12V
21
Analog Input
Analog Input for +12V monitoring.
2.5V
22
Analog Input
Analog Input for +2.5V monitoring..
VCCP
23
Analog Input
Analog Input for VCCP (processor voltage) monitoring.
Remote 1+
18
Remote Thermal
Diode Positive
Input
Positive input (current source) from the first remote thermal
diode Serves as the positive input into the A/D. Connected
to THERMDA pin of Pentium processor.
Remote 1-
17
Remote Thermal
Diode Negative
Input
Negative input (current sink) from the first remote thermal
diode Serves as the negative input into the A/D. Connected
to THERMDC pin of Pentium processor.
Remote 2+
16
Remote Thermal
Diode Positive
Output
Positive input (current source) from the second remote
thermal diode Serves as the positive input into the A/D.
Connected to the base of a diode connected MMBT3904
NPN transistor.
Remote 2-
15
Remote Thermal
Diode Negative
Input
Negative input (current sink) from the second remote
thermal diode Serves as the negative input into the A/D.
Connected to the emitter of a diode connected MMBT3904
NPN transistor.
TACH1
11
Digital Input
Input for monitoring tachometer output of fan 1.
TACH2
12
Digital Input
Input for monitoring tachometer output of fan 2.
TACH3
9
Digital Input
Input for monitoring tachometer output of fan 3. During
power-up, if held low through a 10K
Ω resistor, SMBus
address may be selected based on the state of TACH4 pin.
TACH4/AddressSelect
14
Digital Input
Input for monitoring tachometer output of fan 4. If in
Address Select Mode, determines the SMBus address of
aSC7621.
PWM1/XTESTOUT
24
Digital Open-
Drain Output
Fan speed control 1. When in XOR tree test mode,
functions as XOR Tree output.
PWM2
10
Digital Open-
Drain Output
Fan speed control 2.
PWM3/Address Enable
13
Digital Open-
Drain Output
Fan speed control 3. Pull to ground at power on to enable
Address Select Mode (Address Select pin controls SMBus
address of the device).
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