EVAL-ADT7462EBZ ON Semiconductor, EVAL-ADT7462EBZ Datasheet - Page 45

• Manufacturer Part Number: EVAL-ADT7462EBZ
• Description: BOARD EVALUATION FOR ADT7462
• Manufacturer: ON Semiconductor
• Type: Temperature Sensorr

Specifications of EVAL-ADT7462EBZ

• Contents: Evaluation Board
• For Use With/related Products: ADT7462
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

the Remote 1 temperature channel. The chosen T
is dynamically adjusted based on the current temperature,
operating point, and high and low limits for this zone.
The T
behaves as described in the Automatic Fan Control
Overview section.
Step 10—Monitoring THERM
T
position, while ensuring that the temperature never exceeds
the maximum operating temperature. Using the operating
point limit allows T
issues because of its self−corrective nature. In PC design, the
operating point for the chassis is usually the worst−case
internal chassis temperature.
determined by monitoring the thermal monitor in the Intel
Pentium 4 processor. To do this, the PROCHOT output of
the Pentium 4 is connected to the THERM input of the
ADT7462.
by allowing the current temperature to be copied to the
operating point register when the PROCHOT output pulls
the THERM input low on the ADT7462. This gives the
maximum temperature at which the Pentium 4 can run
before clock modulation occurs.
Enabling the THERM Trip Point as the Operating Point
enable/disable THERM monitoring to program the
operating point. Table 39 details how the remote
MIN
Bit 0 (Remote 1 En) = 1 enables dynamic T
Bit 0 (Remote 1 En) = 0 disables dynamic T
Using the operating point limit ensures that the dynamic
The optimal operating point for the processor is
The operating point for the processor can be determined
Bits [5:2] of Dynamic T
control mode is operating in the best possible acoustic
MIN
AMBIENT TEMP
value chosen is not adjusted, and the channel
REMOTE 1 =
REMOTE 2 =
CPU TEMP
VRM TEMP
LOCAL =
MIN
to be independent of system−level
THERMAL CALIBRATION
THERMAL CALIBRATION
THERMAL CALIBRATION
Figure 74. Acoustic Enhancement Smoothes Fan Speed Variations
MIN
T
T
T
MIN
MIN
MIN
Control Register 1 (0x0B)
T
T
T
RANGE
RANGE
RANGE
Under Automatic Fan Speed Control
100%
100%
100%
MIN
0%
0%
0%
MIN
control on
MIN
control.
http://onsemi.com
MUX
value
45
temperatures can be copied into the operating point registers
on a THERM assertion. Setting these bits to 1 uses the
remote temperature as the operating point temperature,
overwriting the programmed operating point value in the
event of a THERM assertion. Setting these bits to 0 ignores
a THERM assertion, and the operating point register
remains at the programmed value.
Enhancing System Acoustics
to changes in temperature; that is, the PWM duty cycle
responds immediately to temperature change. Any impulses
in temperature can cause an impulse in fan noise. For
psycho−acoustic reasons, the ADT7462 can prevent the
PWM output from reacting instantaneously to temperature
changes. Enhanced acoustic mode controls the maximum
change in PWM duty cycle at a given time. The objective is
to prevent the fan from cycling up and down, annoying the
user.
Acoustic Enhancement Mode Overview
control circuitry on the ADT7462 and shows where acoustic
enhancement fits in. Acoustic enhancement is intended as a
post−design tweak made by a system or mechanical
engineer evaluating best settings for the system. Having
determined the optimal settings for the thermal solution, the
engineer can adjust the system acoustics. The goal is to
implement a system that is acoustically pleasing without
causing user annoyance due to fan cycling. It is important to
realize that although a system might pass an acoustic noise
requirement specification (for example, 36 dB), if the fan is
annoying, it fails the consumer test.
PWM
PWM
PWM
MIN
MIN
MIN
Automatic fan speed control mode reacts instantaneously
Figure 74 gives a top−level overview of the automatic fan
ENHANCEMENT
ACOUSTIC
ENHANCEMENT)
ENHANCEMENT)
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
TACHOMETER 2
MEASUREMENT
TACHOMETER 3
MEASUREMENT
(ACOUSTIC
(ACOUSTIC
(ACOUSTIC
CONTROL
CONTROL
CONTROL
RAMP
RAMP
RAMP
AND 4
GENERATOR
GENERATOR
GENERATOR
CONFIG
CONFIG
CONFIG
PWM
PWM
PWM
PWM
PWM
PWM
PWM1
TACH1
PWM2
TACH2
PWM3
TACH3
FRONT CHASSIS
REAR CHASSIS
CPU FAN SINK