EMC2101-R-ACZL-TR datasheet(44/57 Pages) SMSC

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SMBus Fan Control with 1°C Accurate Temperature Monitoring

Datasheet

Revision 2.54 (06-16-09)

SMSC EMC2101

DATASHEET

The register applies to the fan driver in both PWM and DAC operating modes. The DAC output is

determined by equation [4] below.

These values are independent of the POLARITY bit (see Section 6.16). Therefore, a value of 00h in

the Fan Setting Register will always refer to minimum output drive while a setting of 3Fh in the Fan

Setting Register will always refer to maximum output drive.

APPLICATION NOTE: The output of the DAC driver is dependent upon the current load. With a low current load,

the output will be from 0V to an LSB (approximately 52mV at VDD = 3.3V) below VDD with

a maximum of 64 linear steps.

6.19

PWM Frequency Register

The PWM Frequency Register determines the final PWM frequency and “effective resolution” of the

PWM driver. It has no affect on the DAC output resolution.

It is recommended that this register be set at 1Fh for maximum resolution. See Appendix A "Advanced

PWM Options" for full operation of the PWM_F register and its interactions with the PWM Resolution

and Duty Cycle.

6.20

PWM Frequency Divide Register

This register holds an alternate PWM Frequency divide value that can be used instead of the CLK_SEL

bit function. This register can be written at any time, however unless the CLK_OVR bit is set to a logic

‘1’, it is not used.

When the CLK_OVR bit is set to a logic ‘1’, the PWM Frequency Divide Register is used in conjunction

with the PWM Frequency Register to determine the final PWM frequency that the load will see. When

the CLK_OVR bit is set to a logic ‘0’, the setting of this register is not changed and is not used to

determine the effective PWM frequency.

The PWM frequency when the PWM Frequency Divide Register is used is shown in Equation [5].

[4]

Table 6.24 PWM Frequency Register

ADDR.

R/W

DEFAULT

4Dh

R/W

PWM Frequency

PWM_F[4:0]

17h

Table 6.25 PWM Frequency Divide Register

ADDR.

R/W

DEFAULT

4Eh

R/W

PWM Frequency

Divide

PWM_D[7:0]

01h

FAN

_SETTING

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⎛⎞ V

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