EMC2305 datasheet(39/55 Pages) SMSC

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Multiple RPM-Based PWM Fan Controller for Five Fans

Datasheet

SMSC EMC2305

Revision 1.1 (10-12-09)

DATASHEET

The Fan Configuration 2 registers control the tachometer measurement and advanced features of the

RPM-based Fan Speed Control Algorithm.

Bit 6 - EN_RRCx - Enables ramp rate control when the corresponding fan driver is operated in the

Direct Setting Mode.

‘0’ (default) - Ramp rate control is disabled. When the fan driver is operating in Direct Setting mode,

the fan setting will instantly transition to the next programmed setting.

‘1’ - Ramp rate control is enabled. When the fan driver is operating in Direct Setting mode, the fan

drive setting will follow the ramp rate controls as determined by the Fan Step and Update Time

settings. The maximum fan drive setting step is capped at the Fan Step setting and is updated

based on the Update Time as given by Table 5.13.

Bit 5 - GLITCH_ENx - Disables the low pass glitch filter that removes high frequency noise injected

on the TACHx pin.

‘0’ - The glitch filter is disabled.

‘1’ (default) - The glitch filter is enabled.

Bits 4 - 3 - DER_OPTx[1:0] - Control some of the advanced options that affect the derivative portion

of the RPM-based Fan Speed Control Algorithm as shown in Table 5.15.

Bit 2 - 1 - ERR_RNGx[1:0] - Control some of the advanced options that affect the error window. When

the measured fan speed is within the programmed error window around the target speed, then the fan

drive setting is not updated. The algorithm will continue to monitor the fan speed and calculate

necessary drive setting changes based on the error; however, these changes are ignored.

63h

R/W

Fan 4

Configuration 2

EN_

RRC4

GLITCH_

EN4

DER_OPT4 [1:0]

ERR_RNG4[1:0]

28h

73h

R/W

Fan 5

Configuration 2

EN_

RRC5

GLITCH_

EN5

DER_OPT5 [1:0]

ERR_RN55[1:0]

28h

Table 5.15 Derivative Options

DER_OPTX[1:0]

OPERATION

No derivative options used

Basic derivative. The derivative of the error from

the current drive setting and the target is added

to the iterative Fan Drive Register setting (in

addition to proportional and integral terms)

(default)

Step derivative. The derivative of the error from

the current drive setting and the target is added

to the iterative Fan Drive Register setting and is

not capped by the Fan Step Register.

Both the basic derivative and the step derivative

are used effectively causing the derivative term to

have double the effect of the derivative term.

Table 5.14 Fan Configuration 2 Registers (continued)

ADDR

R/W

DEFAULT

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