EMC2302 datasheet(19/70 Pages) MICROCHIP

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DS20006532A-page 19

EMC2301/2/3/5

4.9

Power-Up Options

The EMC2303/5 allows for one of four fan speed

options upon device power-up depending on the status

of the pull-up resistor on the ADDR_SEL pin and the

CLK pin. If the ADDR_SEL pin decode enables the

CLK pin (see Table 5-1), then the value of the pull-up

resistor on the CLK pin is used to determine the default

fan drive setting (see Section 4.6 “Pull-Up Decode”).

If the Fan Drive setting is set at a non-zero value (as

determined by the CLK pin), then the drive setting will

be set to the desired setting. The Spin Up Routine will

not be activated. This function does not disable the

Watchdog timer which will continue to function

normally. See Section 4.11 “Watchdog Timer”.

4.10

Ramp Rate Control

The Fan Driver can be configured with automatic ramp

rate control. Ramp rate control is accomplished by

adjusting the drive output settings based on the Maxi-

mum Fan Step Register settings and the Update Time

settings.

If the RPM-based Fan Speed Control algorithm is used,

then this ramp rate control is automatically used. The

user programs a maximum step size for the fan drive

setting and an update time. The update time varies

from 100 ms to 1.6s while the fan drive maximum step

can vary from 1 count to 31 counts, and can be set in

When a new fan drive setting is entered, the delta from

the next fan drive setting and the previous fan drive set-

ting is determined. If this delta is greater than the Max

Step settings, then the fan drive setting is incrementally

adjusted every 100 ms to 1.6s as determined by the

Update Time until the target fan drive setting is

reached. See Table 4-3.

FIGURE 4-3:

Ramp Rate Control.

4.11

Watchdog Timer

The EMC2301/2/3/5 contains an internal Watchdog

Timer for all fan drivers. The Watchdog Timer monitors

the SMBus traffic for signs of activity and works in two

different modes based upon device operation. These

modes are Power-Up Operation and Continuous

Operation as described below.

For either mode of operation, if four seconds elapse

without activity detected by the host, then the

Watchdog will be triggered and the following will occur:

The WATCH status bit will be set.

The fan driver will be set to full scale drive. It will

remain at full scale drive until it is disabled.

The ALERT pin will be asserted.

4.11.1

POWER-UP OPERATION

The Watchdog Timer only starts immediately after

power-up. Once it has been triggered or deactivated, it

will not restart although it can be configured to operate

in Continuous operation. While the Watchdog timer is

active, the device will not check for a Stalled Fan

condition.

During the Power-Up Operation, the Watchdog Timer is

disabled by any of the following actions:

Writing the Fan Setting Register will disable the

Watchdog Timer.

Enabling the RPM-based Fan Speed Control

algorithm by setting the ENAGx bit will disable

the Watchdog Timer. The fan driver will be set

based on the RPM-based Fan Speed Control

algorithm.

Writing any other configuration registers will not disable

the Watchdog Timer upon power-up.

4.11.2

CONTINUOUS OPERATION

When configured to operate in Continuous Operation,

the Watchdog Timer will start immediately (see

WD_EN bits in Register 6-2). The timer will be reset by

any access (read or write) to the SMBus register set.

The four second Watchdog Timer will restart upon com-

pletion of SMBus activity.

Setting

Next Desired

Setting

Max

Step

Max

Step

Update

Time

Update

Time

Setting Changed

Note:

When the Watchdog timer is activated, the

Fan Speed Control algorithm is automati-

cally disabled. Disabling the Watchdog

will not automatically set the fan drive nor

re-activate

the

Fan

Speed

Control

algorithm. This must be done manually.

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