NCT7491 Datasheet, PDF (7/81 Pages) ON Semiconductor – Remote Thermal Monitor and Fan Controller

NCT7491
Table 3. QSOP & QFN PACKAGE PIN ASSIGNMENTS
QSOP
Pin No.
QFN
Pin No.
Pin Name
Description
1
22
SDA_S
SMBus/I²C Slave Serial Bi−directional Data Input/Output. Open−drain pin; Re-
quires a pull−up resistor.
2
23
SCL_S
Serial Clock Slave Input. Open−drain pin; Requires a pull−up resistor.
3
24
GND
Ground
4
1
VDD
Positive Supply Voltage
5
2
SDA_M / GPIO1
Open−drain pin; Requires a pull−up resistor.
GPIO1 = General purpose I/O pin
SDA_M = SMBus/I²C Master Serial Bi−directional Data Input/Output.
6
3
SCL_M / GPIO2
Open−drain pin; Requires a pull−up resistor.
GPIO2 = General purpose I/O pin
SCL_M = Serial Clock Master Output.
7
4
PECI
PECI input to report CPU Thermal Information. PECI voltage level is referenced
to the VTT input.
8
5
VTT
Voltage reference for PECI. This is the supply voltage for the PECI interface and
must be present to communicate over the PECI interface.
9
6
TACH3
Fan tachometer input to measure Fan3
10
7
PWM2 / #SMBALERT PWM output to control Fan2. Can be configured as an SMBALERT output.
Open−drain pin; Requires a pull−up resistor.
11
8
TACH1
Fan tachometer input to measure Fan1
12
9
TACH2
Fan tachometer input to measure Fan2
13
10
PWM3 /
#ADDREN
PWM output to control Fan3. If pulled low on power−up the NCT7491 enters
Address Select mode and the ADDRESS SELECT pin determines the slave
address. Open−drain pin; Requires a pull−up resistor.
14
11
TACH4/
Fan Tachometer Input to Measure Speed of Fan 4. May be reconfigured as a
#THERM/
#SMBALERT/
#ADDRESS SELECT
bidirectional THERM. Can be connected to thePROCHOT output of a processor,
to time and monitor PROCHOT assertions. Can be used as an output to signal
an overtemperature condition. The SMBALERT pin is used to signal out−of−limit
comparisons of temperature, voltage, and fan speed. This is compatible with
SMBus alert. Can also be used at device powerup to assign the SMBus ad-
dress. If THERM or SMBALERT is enabled then a pull−up resistor is required.
15
12
16
13
17
14
18
15
19
16
D2−
D2+
D1−
D1+
GPIO3/
#THERM/
#SMBALERT
Negative Connection for Remote Temperature Sensor 2.
Positive Connection for Remote Temperature Sensor 2.
Negative Connection for Remote Temperature Sensor 1.
Positive Connection for Remote Temperature Sensor 1.
General−Purpose Open−Drain Digital Input/Output. Requires a pull−up resistor.
Can be configured as a bidirectional THERM pin or as an SMBALERT pin.
20
17
+5Vin
Analog Input. 0 V to 5 V.
21
18
+12Vin
Analog Input. 0 V to 12 V.
22
19
+2.5V / #THERM
Analog Input. 0 V to 2.5 V. May be reconfigured as a bidirectional THERM pin.
Can be connected to the PROCHOT output of a processor, to time and monitor
PROCHOT assertions. Can be used as an output to signal an overtemperature
condition. In THERM mode it is an open−drain bidirectional pin and requires a
pull up resistor.
23
20
Vccp
Analog input. Monitors CPU core voltage (to maximum 0f 3.0 V). This pin must
be connected to the NCT7491 supply voltage if it is unused.
24
21
PWM1 / XTO
PWM output to control Fan 1. Open−drain pin; Requires a pull−up resistor. Also
functions as the output for the XNOR tree test enable mode.
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