EMC2103 datasheet(58/85 Pages) MICROCHIP

58 / 85 page

RPM-Based Fan Controller with Hardware Thermal Shutdown

Datasheet

DS0005250A-page 58

 2013 Microchip Technology Inc.

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 6.31.

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 6.32 is used as a direct multiplier

term that is applied to the Actual RPM to achieve the Reported RPM. It should only be applied if the

number of edges measured does not match the number of edges expected based on the number of

poles of the fan (which is fixed for any given fan).

Contact Microchip for recommended settings when using fans with more or less than 2 poles.

Table 6.31 Range Decode

RANGE[1:0]

REPORTED MINIMUM

RPM

TACH COUNT

MULTIPLIER

500

1000 (default)

2000

4000

Table 6.32 Minimum Edges for Fan Rotation

EDGES[1:0]

MINIMUM TACH

EDGES

NUMBER OF FAN POLES

EFFECTIVE TACH

MULTIPLIER (BASED ON 2

POLE FANS)

1 pole

0.5

2 poles (default)

3 poles

1.5

4 poles

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