Fan Control Device with High Frequency PWM Support and Hardware Monitoring Features
Datasheet
The INT# pin can be enabled to indicate fan errors. Bit[0] of the Interrupt Enable 2(Fan Tachs) register
(80h) is used to enable this option. This pin will remain low while the associated fan error bit in the
Interrupt Status Register 2 is set.
The INT# pin will remain low while any bit is set in any of the Interrupt Status Registers. Reading the
interrupt status registers will cause the logic to attempt to clear the status bits; however, the status bits
will not clear if the interrupt stimulus is still active. The interrupt enable bit (Special Function Register
bit[2]) should be cleared by software before reading the interrupt status registers to insure that the INT#
pin will be re-asserted while an interrupt event is active, when the INT_EN bit is written to ‘1’ again.
The INT# pin can also be deasserted by issuing an Alert Response Address Call. See the description
in the section titled SMBus Alert Response Address on page 21.
The INT# pin may only become active while the monitor block is operational.
6.6
Low Power Modes
The Hardware Monitor Block can be placed in a low-power mode by writing a ‘0’ to Bit[0] of the
Ready/Lock/Start Register (0x40). The low power mode that is entered is either sleep mode or
shutdown mode as selected using Bit[0] of the Special Function Register (7Ch). These modes do not
reset any of the registers of the Hardware Monitor Block. In both of these modes, the PWM pins are
at 100% duty cycle.
Table 6.4 Low Power Mode Control Bits
START
LPMD
DESCRIPTION
0
0
1
0
1
x
Sleep Mode
Shutdown Mode
Monitoring
Notes:
■
START and LPMD bits cannot be modified when the LOCK bit is set.
■
START bit is located in the Ready/Lock/Start register (40h). LPMD bit is located in the Special
Function Register (7Ch)
6.6.1
6.6.2
Sleep Mode
This is a low power mode in which bias currents are on and the internal oscillator is on, but the the
A/D converter and monitoring cycle are turned off. Serial bus communication is still possible with any
register in the Hardware Monitor Block while in this low-power mode.
Shutdown Mode
This is a low power mode in which bias currents are off, the internal oscillator is off, and the the A/D
converter and monitoring cycle are turned off. Serial communication is only possible with Bits[2:0] of
the Special Function Register at 7Ch and Bits [7:0] of the Configuration Register at 7Fh, which become
write-only registers in this mode.
6.7
Analog Voltage Measurement
The Hardware Monitor Block contains inputs for directly monitoring the power supplies (+12 V, +5 V,
+2.5V, +Vccp, and VCC). These inputs are scaled internally to an internal reference source, converted
via an 8 bit successive approximation register ADC or a Delta-Sigma ADC (Analog-to-Digital
Converter), and scaled such that the correct value refers to 3/4 scale or 192 decimal (except the Vccp
input). This removes the need for external resistor dividers and allows for a more accurate means of
measurement since the voltages are referenced to a known value. Since any of these inputs can be
above VCC or below Ground, they are not diode protected to the power rails. The measured values
SMSC EMC6D103
Revision 0.4 (04-04-05)
DATA2S9HEET
SMSC [ SMSC CORPORATION ]
