ADT7476
Rev. B | Page 51 of 72
Enhanced Acoustics Register 1 (0x62)
Bit 7 MIN3 = 0,
PWM3 is off (0% PWM duty cycle) when
temperature is below T
MIN
− T
HYST
.
Bit 7 MIN3 = 1,
PWM3 runs at PWM3 minimum duty cycle
below T
MIN
− T
HYST
.
Bit 6 MIN2 = 0,
PWM2 is off (0% PWM duty cycle) when
temperature is below T
MIN
− T
HYST
.
Bit 6 MIN2 = 1,
PWM2 runs at PWM2 minimum duty cycle
below T
MIN
− T
HYST
.
Bit 5 MIN1 = 0, PWM1 is off (0% PWM duty cycle) when
temperature is below T
MIN
− T
HYST
.
Bit 5 MIN1 = 1,
PWM1 runs at PWM1 minimum duty cycle
below T
MIN
− T
HYST
.
Configuration Register 6 (0x10)
Bit 0 SLOW = 1, slows the ramp rate for PWM changes
associated with the Remote 1 temperature channel by 4.
Bit 1 SLOW = 1, slows the ramp rate for PWM changes
associated with the local temperature channel by 4.
Bit 2 SLOW = 1, slows the ramp rate for PWM changes
associated with the Remote 2 temperature channel by 4.
Bit 7 ExtraSlow = 1, slows the ramp rate for all fans by a factor
of 39.2%.
The following sections list the ramp-up times when the
SLOW bit is set for each temperature monitoring channel.
Enhanced Acoustics Register 1 (0x62)
Bits [2:0] ACOU,
selects the ramp rate for PWM outputs
associated with the Remote Temperature 1 input.
000 = 37.5 seconds
001 = 18.8 seconds
010 = 12.5 seconds
011 = 7.5 seconds
100 = 4.7 seconds
101 = 3.1 seconds
110 = 1.6 seconds
111 = 0.8 seconds
Enhanced Acoustics Register 2 (0x63)
Bits [2:0] ACOU3,
selects the ramp rate for PWM outputs
associated with the local temperature channel.
000 = 37.5 sec
001 = 18.8 sec
010 = 12.5 seconds
011 = 7.5 seconds
100 = 4.7 seconds
101 = 3.1 seconds
110 = 1.6 seconds
111 = 0.8 seconds
Bits [6:4] ACOU2,
selects the ramp rate for PWM outputs
associated with the Remote 2 temperature input.
000 = 37.5 seconds
001 = 18.8 seconds
010 = 12.5 seconds
011 = 7.5 seconds
100 = 4.7 seconds
101 = 3.1 seconds
110 = 1.6 seconds
111 = 0.8 seconds
When Bit 7 of Configuration Register 6 (0x10) = 1, the above
ramp rates change to the following values:
000 = 52.2 seconds
001 = 26.1 seconds
010 = 17.4 seconds
011 = 10.4 seconds
100 = 6.5 seconds
101 = 4.4 seconds
110 = 2.2 seconds
111 = 1.1 seconds
Setting the appropriate slow bit, Bits [2:0] of Configuration
Register 6 (0x10), slows the ramp rate further by a factor of 4.
FAN PRESENCE DETECT
Fan presence detect is used to determine if a 4-wire fan is
directly connected to a PWM output. This feature does not
work for 3-wire fans. To detect whether a 4-wire fan is con-
nected directly to a PWM output, the following must be
performed in this order:
1.
Drive the appropriate PWM outputs to 100% duty cycle.
2.
Set Bit 0 of Configuration Register 2 (0x73).
3.
Wait 5 ms.
4.
Program fans to run at a different speed if necessary.
5.
Read the state of Bits [3:1] of Configuration Register 2
(0x73). The state of these bits reflects whether a 4-wire fan
is connected directly to the PWM output.
Because the detection time only takes 5 ms, programming the
PWM outputs to 100% and then back to its normal speed is not
noticeable, in most cases.
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