EMC2302 datasheet(14/70 Pages) MICROCHIP

14 / 70 page

EMC2301/2/3/5

DS20006532A-page 14

 2021 Microchip Technology Inc.

4.2

PWM Fan Driver

The EMC2301/2/3/5 supports up to five PWM output

drivers. Each output driver can be configured to oper-

ate as an open-drain (default) or push-pull driver and

can be configured with normal or inverse polarity (see

Additionally, the PWM frequencies are independently

programmable with ranges from 9.5 Hz to 26 kHz in

four programmable frequency bands shown in Table 4-

2 (see Register 6-9 and Register 6-10).

The frequency of the PWM drive can further be tuned

through the PWM Frequency Divide Registers (see

divides the base frequency, allowing the 9.5 Hz PWM

frequency to be generated from the 2441 Hz Base Fre-

quency. A value of 00h or 01h in the PWM Frequency

Divide Register is decoded as 01h.

4.3

RPM-Based Fan Speed Control

Algorithm

The EMC2301/2/3/5 includes up to five RPM-based

Fan Speed Control algorithms. Each algorithm oper-

ates independently and controls a separate fan driver.

Each algorithm is controlled manually (by setting the

target fan speed).

This fan control algorithm uses proportional, integral,

and derivative terms to automatically approach and

maintain the system’s desired fan speed to an accu-

racy directly proportional to the accuracy of the clock

source.

The desired tachometer count is set by the user input-

ting the desired number of 32.768 kHz cycles that

occur per fan revolution. This is done by manually set-

ting the TACH Target Register. The user may change

the target count at any time. The user may also set the

target count to FFh in order to disable the fan driver for

lower current operation.

For example, if a desired RPM rate for a 2-pole fan is

3000 RPM, then the user would input the hexadecimal

equivalent of 1296 (51h in the TACH Target Register).

This number represents the number of 32.768 KHz

cycles that would occur during the time it takes the fan

to complete a single revolution when it is spinning at

3000 RPM.

The EMC2301/2/3/5’s RPM-based Fan Speed Control

algorithm has programmable configuration settings for

parameters such as ramp-rate control and spin up con-

ditions. The fan driver automatically detects and

attempts to alleviate a Stalled/Stuck fan condition while

also asserting the ALERT pin. The EMC2301/2/3/5

works with fans that operate up to 16000 RPM and

provide a valid tachometer signal.

The fan controller will function either with an externally

supplied 32.768 kHz clock source or with its own inter-

nal 32 kHz oscillator depending on the required accu-

racy. The EMC2301/2/3/5 offers a clock output that

enables additional devices to be set as clients to the

same clock source.

The update rate of the PID loop and Ramp Rate Con-

trol is controlled by the Fan Configuration 1 and 2 Reg-

isters settings (see Register 6-13 and Register 6-14).

The values for the Update Time settings in the Fan

Configuration 1 register are shown in Table 4-3.

TABLE 4-1:

FAN CONTROLS ACTIVE FOR

OPERATING MODE

Direct Setting Mode

FSC Mode

Fan Driver Setting

(Read/Write)

Fan Driver Setting

(Read Only)

EDGES[1:0]

(Fan Configuration)

—

RANGE[1:0]

(Fan Configuration)

UPDATE[2:0]

(Fan Configuration)

UPDATE[2:0]

(Fan Configuration)

LEVEL

(Spin Up Configuration)

LEVEL

(Spin Up Configuration)

SPINUP_TIME[1:0]

(Spin Up Configuration)

SPINUP_TIME[1:0]

(Spin Up Configuration)

Fan Step

—

Fan Minimum Drive

Valid TACH Count

—

TACH Target (Read/Write)

TACH Reading

—

DRIVE_FAIL_CNT[1:0]

and Drive Band Fail

Registers

TABLE 4-2:

PWM_BASEX BIT DECODE

PWM_BASEX[1:0]

Base Frequency

26.00 kHz (default)

19.531 kHz

4.882 kHz

2.441 kHz

TABLE 4-3:

UPDATE TIME

UPDATEX[2:0]

Update

Time

100 ms

200 ms

300 ms

400 ms

(default)

500 ms

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