EMC2104 datasheet(67/101 Pages) SMSC

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Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown

Datasheet

SMSC EMC2104

Revision 1.74 (05-08-08)

DATASHEET

6.23

Fan Configuration 2 Registers

The Fan Configuration 2 Register controls 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 or the Direct Setting with LUT mode.

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

or Direct Setting with LUT 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 or Direct

Setting with LUT 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 6.31.

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

on the TACHx pin. If the LOWDRIVE bit is set, this bit is ignored and the filter is automatically disabled.

‘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 6.33.

Table 6.32 Fan Configuration 1 Registers

ADDR

R/W

DEFAULT

43h

R/W

Fan 1

Configuration

EN_

RRC1

GLITCH

_EN1

DER_OPT1 [1:0]

ERR_RNG[1:0]

LOWD

RIVE1

38h

83h

R/W

Fan 2

Configuration

EN_

RRC2

GLITCH

_EN2

DER_OPT2 [1:0]

ERR_RNG[1:0]

LOWD

RIVE2

38h

Table 6.33 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)

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

(default).

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