Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
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.
Table 5.1 SHDN_SEL Pin Configuration
FUNCTION
NAME
CRITICAL / THERMAL
SHUTDOWN RANGE
SHDN_SEL
TEMPERATURE MONITORING FEATURES
0
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
Low - 60°C to 122°C
Low - 60°C to 122°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.
1
Internal
The internal diode is linked to the Hardware set
Thermal / Critical shutdown circuitry and the
SYS_SHDN# pin.
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.
SMSC EMC2104
Revision 1.74 (05-08-08)
DATA2S3HEET
SMSC [ SMSC CORPORATION ]
