EMC2104 datasheet(22/101 Pages) SMSC

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Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown

Datasheet

Revision 1.74 (05-08-08)

SMSC EMC2104

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.

Figure 5.2 EMC2104 Critical/Thermal Shutdown Block Diagram

Voltage

Conversion

SYS_SHDN#

TRIP_SET

External Diode 1

Critical Shutdown Logic

SMBus Traffic

SW_SHDN

Configuration

VREF

SHDN_SEL

PIN Decode

‘1’

Temperature

Conversion

Sensor

Internal Diode

Channel

HW_SHDN

Temperature

Conversion

and Limit

Registers

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