EMC2103 datasheet(65/85 Pages) MICROCHIP

65 / 85 page

RPM-Based Fan Controller with Hardware Thermal Shutdown

Datasheet

 2013 Microchip Technology Inc.

DS0005250A-page 65

If the algorithm is enabled then setting the TACH Target Register to FFh will disable the fan driver (set

the PWM duty cycle to 0%). Setting the TACH Target to any other value (from a setting of FFh) will

cause the algorithm to invoke the Spin Up Routine after which it will function normally.

6.31

TACH Reading Register

The TACH Reading Register contents describe the current tachometer reading for the fan. By default,

the data represents the fan speed as the number of 32kHz clock periods that occur for a single

revolution of the fan.

Equation [3] shows the detailed conversion from TACH measurement (COUNT) to RPM while Equation

[4] shows the simplified translation of TACH Reading Register count to RPM assuming a 2-pole fan,

measuring 5 edges, with a frequency of 32.768kHz.

These equations are solved and tabulated for ease of use in AN17.4 RPM to TACH Counts

Conversion.

6.32

Look Up Table Configuration Register

The Look Up Table Configuration Register controls the setup information for the temperature to fan

drive look up table.

Bit 7 - USE_DTS_F1 - This bit determines whether the Pushed Temperature 1 Register is using DTS

data.

Table 6.48 TACH Reading Register

ADDR

R/W

DEFAULT

4Eh

Fan TACH

4096

2048

1024

512

256

128

FFh

4Fh

Fan TACH

Low Byte

8421

F8h

where:

[3]

poles = number of poles of the fan

(typically 2)

n = number of edges measured

(typically 5)

m = the multiplier defined by the

RANGE bits

[4]

COUNT = TACH Reading Register

value (in decimal)

Table 6.49 Look Up Table Configuration Register

ADDR

R/W

DEFAULT

50h

R/W

LUT

Configuration

USE_D

TS_F1

USE_D

TS_F2

LUT_L

OCK

RPM /

PWM

TEMP3

_CFG

TEMP4

_CFG

00h

RPM

poles



--------------------

–



COUNT

-----



----------------------------------

1,966,080



RPM

3,932,160



COUNT

--------------------------------------

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