LPC47B272-MS SMSC, LPC47B272-MS Datasheet - Page 122

• Manufacturer Part Number: LPC47B272-MS
• Description: IC CTRLR SUPER I/O LPC 100-QFP
• Manufacturer: SMSC

Specifications of LPC47B272-MS

• Controller Type: I/O Controller
• Interface: LPC
• Voltage - Supply: 3.3V
• Current - Supply: 15mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 100-QFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 638-1019

limit” of the RPM for the fan by programming the divisor and preload value accordingly. Typical practice
is to consider 70% of normal RPM a fan failure, at which point Term 1 in Equation 1 for the example
above will be 160. Therefore, the preload value is chosen to be 32 so that when the count reaches 192,
this will correspond to 70% of the normal RPM for the generation of a PME or SMI.
A representation of the logic for the fan tachometer implementation is shown below.
The following tables show examples of the desired functionality. Counts are based on 2 pulses per
revolution tachometer outputs with a default divisor of 2.
Pins 51 and 52 are the fan tachometer inputs, FAN_TACH2 and FAN_TACH1, respectively.
The configuration registers for the fan tachometer inputs are defined in the “Runtime Registers” section.
SMSC LPC47B27x
Divide by 1
Divide by 2
Divide by 4
Divide by 8
RPM
4400
3080
2640
2204
Select
Mode
Revolution
Time per
13.64 ms
19.48 ms
22.73 ms
27.22 ms
Nomina
32 kHz
l RPM
8800
4400
2200
1100
2” (Default) in Decimal
Term 1 for “Divide by
Revolution
Time per
13.64 ms
27.27 ms
54.54 ms
6.82 ms
Programmable
1, 2, 4, 8
112 counts
160 counts
186 counts
223 counts
Divider
DATASHEET
Preload
32
32
32
32
Latch on Read
Preload
Counter
- 122 -
Preload
Given Speed in
Counts for the
32
32
32
32
MSB
Decimal
144
144
144
144
(Term 1) + Preload
(maximum count)
Sync
Count =
144
192
218
255
RPM
6160
3080
1540
70%
770
To nPME
Logic
Revolution for
70% RPM
Time per
19.48 ms
38.96 ms
77.92 ms
Comments
9.74 ms
70% RPM
60% RPM
50% RPM
Rev. 04-17-07
Typical
RPM