EMC6D103 datasheet(45/92 Pages) SMSC

45 / 92 page

Fan Control Device with High Frequency PWM Support and Hardware Monitoring Features

Datasheet

SMSC EMC6D103

Revision 0.3 (03-01-07)

DATASHEET

-Mode 1: If the programmed number of edges occurs before the counter reaches FFFFh latch the

tachometer count

-Mode 2: If the programmed number of edges occurs during the PWM ‘ON’ time or stretching time:

latch the tachometer count and stop stretching PWM (see Note below).

Notes:

Whenever the programmed number of edges is detected, the edge detection ends and the state

machine is reset. The tachometer reading register is updated with the tachometer count value at

this time. See Note 7.2 below Table 7.2 for the one exception to this behavior.

In the case where the programmed number of edges occurs during the stretching time, the

tachometer value is latched when the last required edge is detected. The table below shows the

maximum values that may appear in the reading register.

Note 7.1

The maximum tachometer count does not take into account the guard time.

Note 7.2

This max value will be FFFFh if the programmed number of edges is detected when the

count reaches FFFFh or if no edges are detected. If the count reaches FFFFh in Mode 1

or the Max stretch time in Mode 2 and some edges were detected, but less than the

programmed number of edges, the maximum tach count value is determined by the Slow

Interrupt Enable bit located in the TACHx Options registers at offsets 90h to 93h. If slow

interrupt detection is set to 0, the count will be forced to FFFEh, else the count will be

forced to FFFFh.

7.1.4.8

Examples of Minimum RPMs Supported

The following tables show minimum RPMs that can be supported with the different parameters. The

first table uses 3 edges and the second table uses 2 edges.

Table 7.2 Max Tachometer Count Values for Different Stretch Periods

PWM STRETCHING PERIOD

MAXIMUM TACHOMETER COUNT AT END OF PERIOD

(Note 7.1)

50ms

1194h

100ms

2328h

200ms

4650h

400ms

8CA0h

600ms

D2F0h

800ms

FFFFh (Note 7.2)

950ms

FFFFh (Note 7.2)

EMC6D103 Datasheet(PDF) 45 Page - SMSC Corporation

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