EMC2101-R-ACZL-TR datasheet(21/57 Pages) SMSC

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SMBus Fan Control with 1°C Accurate Temperature Monitoring

Datasheet

SMSC EMC2101

Revision 2.54 (06-16-09)

DATASHEET

command can be issued that will refresh the temperature data. The limits are only checked when

the temperature data is updated.

3. Mixed - the temperature monitoring block is disabled, but the fan driver block is active. The device

will not update temperature data automatically and the fan driver output will not be updated

automatically based on temperature. A one-shot command can be issued that will refresh the

temperature data and update the fan driver based on the values in the Fan Control Look-Up Table

(if the Fan Control Look-Up Table is enabled).

5.4

ALERT / TACH Output

The ALERT / TACH pin (Pin 6) is an open drain output and requires a pull-up resistor to VDD when

configured as an ALERT output.

APPLICATION NOTE: When configured as a TACH input, the ALERT / TACH pin will not function as an ALERT

output. Error conditions will not trigger an interrupt (though will be updated in the Status

Registers as normal) and the MASK bits will do nothing. Likewise, the device will not respond

to the ARA command.

For the EMC2101-R, the value of this pull-up resistor determines the initial FAN output mode of

operation as well as whether the device auto loads from an EEPROM or via an SMBus host per

Table 5.1.

After power-up, the EMC2101-R requires 10ms to initialize and determine the operating mode.

When configured as an interrupt, the ALERT / TACH pin is maskable for each alert condition. If the

ALERT / TACH pin is masked, then it will not respond to the corresponding condition (though the Alert

Status Register will update normally). This pin has multiple functions described below and is controlled

by ALERT_COMP bit (bit 0) in the Averaging Filter Register (BFh) (see Section 6.23).

5.4.1

ALERT / TACH as a Temperature Comparator

When the ALERT / TACH pin is used as a temperature comparator, the ALERT / TACH output is

asserted when an out of limit measurement (> high limit, < low limit, or > TCRIT limit) is detected on

any diode (low limits only apply to the external diode channel) or when the external diode connections

are open. When the condition is no longer true, the ALERT / TACH output will de-assert. Reading from

the Status Register will cause the ALERT / TACH pin to be released however it will not prevent it from

being re-asserted based on the temperature comparisons.

Setting the MASK bit will not affect the ALERT / TACH pin when it is configured as a temperature

comparator, however the individual channel mask bits will block the ALERT / TACH pin from being

asserted.

Table 5.1 ALERT/ TACH Pull-up Resistors - SMBus / FAN MODE for EMC2101-R

ALERT / TACH

PULL-UP RESISTOR

SMBUS MODE

FAN MODE

POLARITY BIT

SETTING (SEE

Section 6.16)

5.6k Ohm ±5%

Host Load via SMBus

FAN output initialize to 100%

Duty Cycle

10k Ohm ±5%

Host Load via SMBus

FAN output initialize to 0% Duty

Cycle

18k Ohm ±5%

Auto Load via

EEPROM

FAN output initialize to 100%

Duty Cycle

33k Ohm ±5%

Auto Load via

EEPROM

FAN output initialize to 0% Duty

Cycle

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