EMC6D103 datasheet(44/89 Pages) SMSC

44 / 89 page

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

Datasheet

Revision 0.4 (04-04-05)

SMSC EMC6D103

DATASHEET

Figure 7.5 PWM and Tachometer Concept

FAN TACHOMETER OPTIONS FOR MODE 2

■

2, 3, 5 or 9 “edges” to calculate the fan speed (Figure 7.5)

■

Guard time A is programmable (8-63 clocks) to account for delays in the system (Figure 7.5)

■

The PWM frequencies for modes 1 & 2 are: 11.0 Hz, 14.6 Hz, 21.9 Hz, 29.3 Hz, 35.2 Hz, 44.0 Hz,

58.6 Hz, 87.7Hz and 25Khz

■

Option to ignore first 3 tachometer edges after guard time

■

Option to force tach reading register to FFFEh to indicate a slow fan.

7.1.4.5

Fan Tachometer Reading Registers:

The Tachometer Reading registers are 16 bits, unsigned. When one byte of a 16-bit register is read, the

other byte latches the current value until it is read, in order to ensure a valid reading. The order is LSB first,

MSB second. The value FFFFh indicates that the fan is not spinning, or the tachometer input is not

connected to a valid signal (this could be triggered by a counter overflow). These registers are read

only – a write to these registers has no effect.

Notes:

■

The Fan Tachometer Reading registers always return an accurate fan tachometer measurement,

even when a fan is disabled or non-functional.

■

FFFFh indicates that the fan is not spinning, or the tachometer input is not connected to a valid

signal (This could be triggered by a counter overflow).

■

The Tachometer registers are read only – a write to these registers has no effect.

■

Mode 1 should be enabled and the tachometer limit register should be set to FFFFh if a tachometer

input is left unconnected.

Internal PWM

Signal

Window for

Valid Tach

Pulses

Guard time A

Tach

Pulses

Tach

Pulses

PWM “ON”

EMC6D103 Datasheet(PDF) 44 Page - SMSC Corporation

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