EMC2104 datasheet(23/101 Pages) SMSC

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Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown

Datasheet

SMSC EMC2104

Revision 1.74 (05-08-08)

DATASHEET

5.1.1

SHDN_SEL Pin

The EMC2104 has a ‘strappable’ input (SHDN_SEL) allowing for configuration of the hardware

Critical/Thermal Shutdown input channels. This pin has 3 possible states and is monitored and

decoded by the EMC2104 at power-up. The three possible states are 0 (tied to GND), 1 (tied to 3.3V)

or High-Z (open). The state of this pin determines which external diode configuration is used for the

Critical / Thermal shutdown function.

The different configurations of the SHDN_SEL pin are described in Table 5.1. SHDN_SEL applies only

to the selected temperature channel.

5.1.2

TRIP_SET / VIN4 Pin

The EMC2104’s TRIP_SET / VIN4 pin is an analog input to the Critical/Thermal Shutdown block which

sets the Thermal Shutdown temperature. The system designer creates a voltage level at the input

through a simple resistor connected to GND as shown in Figure 5.1. The value of this resistor is used

to create an input voltage on the TRIP_SET / VIN4 pin which is translated into a temperature ranging

from 60°C to 122°C or 90°C to 152°C as enumerated in Table 5.2.

When the SHDN_SEL pin is pulled to ‘1’ at power up, then the TRIP_SET / VIN4 pin is configured to

measure VIN4 as its primary function. The circuitry will still calculate the thermal / critical shutdown

threshold based on the voltage and compare this temperature against the Internal Diode temperature.

This will cause the SYS_SHDN# pin to assert if the measured temperature exceeds this threshold.

The device will also compare the measured voltage against the VIN4 High and Low limits. This function

is not available if SHDN_SEL is set to ‘0’ or ‘High-Z’ at power up.

APPLICATION NOTE: If the SHDN_SEL pin is pulled to ‘1’ at power up and the TRIP_SET / VIN4 pin is intended

for use as a voltage input then the SYS_SHDN# pin should be ignored.

APPLICATION NOTE: If the SHDN_SEL pin is pulled to ‘1’ at power up and the TRIP_SET / VIN4 pin is intended

to be used to set a threshold level then the VIN4 channel should be masked. Furthermore,

the voltage on the pin must be externally generated based on Equation [1]. Do not use

Table 5.2.

APPLICATION NOTE: When used in its TRIP_SET mode (i.e. the SHDN_SEL pin is not set to a logic ‘1’), current

only flows when the TRIP_SET / VIN4 pin is being monitored. At all other times, the internal

reference voltage is removed and the TRIP_SET / VIN4 pin will be pulled down to ground.

Table 5.1 SHDN_SEL Pin Configuration

SHDN_SEL

FUNCTION

NAME

TEMPERATURE MONITORING FEATURES

CRITICAL / THERMAL

SHUTDOWN RANGE

Intel Transistor

Mode (substrate

PNP)

The external diode 1 channel is configured with

Beta Compensation enabled and Resistance

Error Correction enabled. This mode is ideal

for monitoring a substrate transistor such as an

Intel CPU thermal diode.

High - 92°C to 154°C

High-Z (open)

AMD CPU /

Diode Mode

The external diode 1 channel is configured with

Beta Compensation disabled and Resistance

Error Correction disabled. This mode is ideal

for monitoring an AMD processor diode or a

2N3904 diode.

Low - 60°C to 122°C

Internal

The internal diode is linked to the Hardware set

Thermal / Critical shutdown circuitry and the

SYS_SHDN# pin.

Low - 60°C to 122°C

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