EMC2302 datasheet(18/70 Pages) MICROCHIP

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EMC2301/2/3/5

DS20006532A-page 18

 2021 Microchip Technology Inc.

4.7

External Clock

The EMC2301/2/3/5 allows the user to choose

between supplying an external 32.768 kHz clock or use

of the internal 32 kHz oscillator to measure the tachom-

eter signal. This clock source is used by the RPM-

based Fan Speed Control algorithm to calculate the

current fan speed. This fan controller accuracy is

directly proportional to the accuracy of the clock

source.

When this function is used, the external clock is driven

into the device via the CLK pin.

4.7.1

INTERNAL CLOCK

Alternately, the EMC2301/2/3/5 may be configured to

use its internal clock as a clock output to drive other fan

driver devices. When configured to operate in this

mode, the device uses its internal clock for tachometer

reading and drives the CLK pin using a push-pull driver.

4.8

Spin Up Routine

The EMC2301/2/3/5 also contains programmable cir-

cuitry to control the spin up behavior of the fan driver to

ensure proper fan operation. This circuitry is controlled

though the Spin-Up Configuration register (see

The Spin Up Routine is initiated in the Direct Setting

mode when the setting value changes from 00h to

anything else.

When the Fan Speed Control algorithm is enabled, the

Spin Up Routine is initiated under the following

conditions:

The TACH Target Register value changes from

a value of FFh to a value that is less than the

Valid TACH Count (see Register 6-19).

The RPM-based Fan Speed Control algorithm’s

measured TACH Reading Register value is

greater than the Valid TACH Count setting.

When the Spin Up Routine is operating, the fan driver

is set to full scale (optional) for one quarter of the total

user defined spin up time. For the remaining spin up

time, the fan driver output is set at a user-defined level

as shown in Table 4-10.

The amount of time allocated to the Spin Up Routine is

also selectable using the SPT bits within Register 6-16.

The times available are shown in Table 4-11.

After the Spin Up Routine has finished, the EMC2301/

2/3/5 measures the TACHx signal. If the measured

TACH Reading Register value is higher than the Valid

TACH Count Register setting, the FNSPIN status bit

(see Register 6-2) is set and the Spin Up Routine will

automatically attempt to restart the fan.

Figure 4-2 shows an example of the Spin Up Routine in

response to a programmed fan speed change based

on the first condition above.

FIGURE 4-2:

Spin Up Routine.

TABLE 4-9:

CLK PIN PULL-UP DECODE

Pull-Up Resistor

Fan Default Drive

Setting

4.7k Ohm ±5%

0% - OFF

6.8k Ohm ±5%

30%

10k Ohm ±5%

50%

15k Ohm ±5%

75%

22k Ohm ±5%

100%

33k Ohm ±5%

0% - OFF

TABLE 4-10:

SPIN LEVEL

SPLVX[2:0]

Spin Up Drive Level

30%

35%

40%

45%

50%

55%

60% (default)

65%

TABLE 4-11:

SPIN TIME

SPTX[1:0]

Total Spin Up

Time

250 ms

500 ms (default)

1 sec

2 sec

100%

(optional)

30% th rough 65 %

F an S tep

Sp in U p T im e

¼ o f S p in U p T ime

U pdate T im e

Tach Targe t C o un t

C han ge d

Tach T a rg et

Co u n t Re a ch e d

Ne w T a rg e t

C ount

P rev T a rg et

C ount = F F h

C heck T A C H

Kick

A lgorithm

c ontro lled

Kick

S p in -up

c ontro lled

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