Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
Datasheet
5.1
Critical/Thermal Shutdown
The EMC2104 provides a hardware Critical/Thermal Shutdown function for systems. Figure 5.2 is a
block diagram of this Critical/Thermal Shutdown function. The Critical/Thermal Shutdown function in
the EMC2104 accepts configuration information from the fixed states of the SHDN_SEL pin as
described in Section 5.1.1.
Each of the software programmed temperature limits can be optionally configured to act as inputs to
the Critical / Thermal Shutdown independent of the hardware shutdown operation. When configured to
operate this way, the SYS_SHDN# pin will be asserted when the temperature meets or exceeds the
limit. The pin will be released when the temperature drops below the limit however the individual status
bits will not be cleared if set (see Section 6.13).
The analog portion of the Critical/Thermal Shutdown function monitors the hardware determined
temperature channel (see Section 5.1.1). This measured temperature is then compared with
TRIP_SET point. This TRIP_SET point is set by the system designer with a single external resistor
divider as described in Section 5.1.2.
The SYS_SHDN# is asserted when the indicated temperature exceeds the temperature threshold
established by the TRIP_SET input pin for a number of consecutive measurements defined by the fault
queue. If the HW_SHDN output is asserted and the temperature drops below the Thermal / Critical
Shutdown threshold then it will be set to a logic ‘0’ state.
Register Enabled
Critical Shutdown Logic
Sensor
SMBus Traffic
Register Enabled
Sensor
Configuration
Register
Temperature
Conversion
and Limit
Register Enabled
Sensor
Registers
SW_SHDN
Register Enabled
Sensor
PIN Decode
‘1’
Internal Diode
Channel
SHDN_SEL
External Diode 1
Temperature
Conversion
1
VREF
SYS_SHDN#
HW_SHDN
0
TRIP_SET
Voltage
Conversion
Figure 5.2 EMC2104 Critical/Thermal Shutdown Block Diagram
Revision 1.74 (05-08-08)
SMSC EMC2104
DATA2S2HEET
SMSC [ SMSC CORPORATION ]
