EMC2101-R-ACZL-TR datasheet(41/57 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

The TACH Limit Registers store the maximum TACH count that the fan is expected to operate at.

TACH count is inversely proportional to the actual fan speed. This limit is used to guarantee that the

fan has spun up properly. If the measured TACH is higher than this limit (indicating that the fan speed

is lower than the minimum RPM value), then the TACH bit is set in the Status Register.

Additionally if the measured TACH count exceeds this limit, depending on the status of the

TACH_M[1:0] bits (see Section 6.16), the TACH reading registers may be forced to FFFFh.

6.16

Fan Configuration Register

The Fan Configuration Register enables the Fan Control Look-Up Table and polarity of the PWM signal

driving the output.

Bit 6 - FORCE - enables the External Temperature Force Register. This bit is not used if the Fan

Control Look-Up Table is not used.

‘0’ (default) - the External Diode Force Register is not used. The measured External Diode

temperature is used to determine the position in the Fan Control Look-Up Table.

‘1’ - the External Temperature Force Register is used. When determining the position in the Fan

Control Look-Up Table, the contents of the External Temperature Force Register will be used

instead of the measured External Diode temperature. All limits will be checked against the

measured External Diode temperature as normal.

Bit 5 - PROG - enables the Fan Control Look-Up Table for update and sets fan driver output based

on Fan Control Look-Up Table values.

‘0’ - the Fan Setting Register and Fan Control Look-Up Table Registers are read-only and the Fan

Control Look-Up Table Registers will be used.

‘1’ (default) - the Fan Setting Register and Fan Control Look-Up Table Registers can be written.

The value written into the Fan Setting Register will be instantly applied to the fan driver and the

Fan Control Look-Up Table will not be used.

Bit 4 - POLARITY- sets the polarity of the Fan output driver. For the EMC2101-R, the value of this bit

is determined by the value of the pull-up resistor on the ALERT / TACH pin (see Table 5.1). When the

PWM default value is set at 100% duty cycle, the default value is set to ‘1’ and when the PWM default

value is set to 0% duty cycle, the default value is set to ‘0’. This occurs within 10ms after power-up.

‘0’ (default - EMC2101) - The polarity of the Fan output driver is non-inverted. A ‘00h’ setting will

correspond to a 0% duty cycle or minimum DAC output voltage.

‘1’ - The polarity of the Fan output driver is inverted. A ‘00h’ setting will correspond to a 100% duty

cycle or maximum DAC output voltage.

Bit 3 - CLK_SEL - Determines the base clock that is used to determine the final PWM frequency.

‘0’ (default) - The base clock that is used to determine the PWM frequency is 360kHz.

‘1’ - The base clock that is used to determine the PWM frequency is 1.4kHz.

Bit 2 - CLK_OVR - Overrides the CLK_SEL bit and uses the Frequency Divide Register to determine

the base PWM frequency. It is recommended that this bit be set for maximum PWM resolution.

‘0’ (default) - The base clock frequency for the PWM is determined by the CLK_SEL bit.

‘1’ (recommended) - The base clock that is used to determine the PWM frequency is set by the

Frequency Divide Register

Table 6.18 Fan Configuration Register

ADDR.

R/W

DEFAULT

4Ah

R/W

Fan Config

FORCE

PROG

POLARITY

CLK_

SEL

CLK_

OVR

TACH_M[1:0]

20h

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