EMC2103 datasheet(55/84 Pages) SMSC

55 / 84 page

RPM-Based Fan Controller with HW Thermal Shutdown

Datasheet

SMSC EMC2103

Revision 0.85 (01-29-08)

DATASHEET

The PWM Divide Register determines the final frequency of the PWM driver. The driver base frequency

is divided by the value of the PWM Divide Register to determine the final frequency. The duty cycle

settings are not affected by these settings, only the final frequency of the PWM driver. A value of 00h

will be decoded as 01h.

The final PWM frequency is derived as the base frequency divided by the value of this register as

shown in Equation [2].

6.22

Fan Configuration 1 Register

The Fan Configuration 1 Register controls the general operation of the RPM based Fan Speed Control

Algorithm used on the PWM pin.

Bit 7 - EN_ALGO - enables the RPM based Fan Speed Control Algorithm. Based on the setting of the

RPM / PWM bit, this bit is automatically set or cleared when the LUT_LOCK bit is set (see

Section 6.32).

‘0’ - (default) the control circuitry is disabled and the fan driver output is determined by the Fan

Driver Setting Register.

‘1’ - the control circuitry is enabled and the Fan Driver output will be automatically updated to

maintain the programmed fan speed as indicated by the TACH Target Register.

Bits 6- 5 - RANGE[1:0] - Adjusts the range of reported and programmed tachometer reading values.

The RANGE bits determine the weighting of all TACH values (including the Valid TACH Count, TACH

Target, and TACH reading) as shown in Table 6.30.

Bits 4-3 - EDGES[1:0] - determines the minimum number of edges that must be detected on the TACH

signal to determine a single rotation. A typical fan measured 5 edges (for a 2-pole fan). For more

accurate tachometer measurement, the minimum number of edges measured may be increased.

Increasing the number of edges measured with respect to the number of poles of the fan will cause

the TACH Reading registers to indicate a fan speed that is higher or lower than the actual speed. In

order for the FSC Algorithm to operate correctly, the TACH Target must be updated by the user to

accommodate this shift. The Effective Tach Multiplier shown in Table 6.31 is used as a direct multiplier

[2]

Table 6.29 Fan Configuration 1 Register

ADDR

R/W

DEFAULT

42h

R/W

Fan

Configuration 1

EN_

ALGO

RANGE[1:0]

EDGES[1:0]

UPDATE[2:0]

2Bh

Table 6.30 Range Decode

RANGE[1:0]

REPORTED MINIMUM

RPM

TACH COUNT

MULTIPLIER

500

1000 (default)

2000

4000

PWM

PWM base freqeuncy

PWM Divide Setting

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EMC2103 Datasheet(PDF) 55 Page - SMSC Corporation

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