LM85 National Semiconductor, LM85 Datasheet - Page 20

• Manufacturer Part Number: LM85
• Description: Hardware Monitor with Integrated Fan Control
• Manufacturer: National Semiconductor

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Register
Address
64h
65h
66h
Functional Description
4.17 Registers 64-66h: Minimum PWM Duty Cycle
These registers specify the minimum duty cycle that the PWM will output when the measured temperature reaches the
Temperature LIMIT register setting.
This register becomes Read Only when the Ready/Lock/Start/Override register Lock bit is set. Any further attempts to write to this
register shall have no effect. After power up the default value is used whenever the Ready/Lock/Start/Override register Start bit
is cleared even though modifications to this register are possible.
Read/
Write
R/W
R/W
R/W
FIGURE 2. What LM85 Auto Fan Control Sees With and Without Spike Smoothing
Register
Name
Fan1 PWM Minimum
Fan2 PWM Minimum
Fan3 PWM Minimum
TABLE 8. PWM Output Below Limit Depending on Value of Off/Min
Off/Min
0
1
ZN-X[2:0]
000
001
010
011
100
101
110
111
(Continued)
Bit 7
(MSB)
7
7
7
PWM Action
At 0% duty below LIMIT
At Min PWM Duty below LIMIT
TABLE 7. Spike Smoothing
Bit 6
6
6
6
Spike Smoothed Over
35 seconds
17.6 seconds
11.8 seconds
7.0 seconds
4.4 seconds
3.0 seconds
1.6 seconds
.8 seconds
Bit 5
5
5
5
20
Bit 4
4
4
4
Bit 3
3
3
3
20035307
Bit 2
2
2
2
Bit 1
1
1
1
Bit 0
(LSB)
0
0
0
Default
Value
80h
80h
80h
Lock?
U
U
U