ADT7473ARQZ-REEL7 ON Semiconductor, ADT7473ARQZ-REEL7 Datasheet - Page 51

• Manufacturer Part Number: ADT7473ARQZ-REEL7
• Description: IC REMOTE THERMAL CTRLR 16QSOP
• Manufacturer: ON Semiconductor
• Series: dBCool®r

Specifications of ADT7473ARQZ-REEL7

• Function: Fan Control, Temp Monitor
• Topology: ADC, Comparator, Fan Speed Counter, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: SMBus™
• Output Alarm: No
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 3.6 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

it takes for the PWM output to ramp up from 0% to 100%
duty cycle for an instantaneous change in temperature. This
can be tested by putting the ADT7473/ADT7473−1 into
manual mode and changing the PWM output from 0% to
100% PWM duty cycle. The PWM output takes 35 seconds
to reach 100% when a ramp rate of 1 time slot is selected.
PWM duty cycle for enhanced acoustics mode. The ramp
rate is set to 48, which corresponds to the fastest ramp rate.
Assume that a new temperature reading is available every
115 ms. With these settings, it takes approximately 0.76
seconds to go from 33% duty cycle to 100% duty cycle (full
speed). Even though the temperature increases very rapidly,
the fan ramps up to full speed gradually.
8 affects the control loop. The overall response of the fan is
slower. Because the ramp rate is reduced, it takes longer for
the fan to achieve full running speed. In this case, it takes
approximately 4.4 seconds for the fan to reach full speed.
Another way to view the ramp rates is to measure the time
Figure 77 shows remote temperature plotted against
Figure 78 shows how changing the ramp rate from 48 to
120
100
140
120
100
80
60
40
20
80
60
40
20
0
0
0
0
Figure 77. Enhanced Acoustics Mode with
Figure 78. Enhanced Acoustics Mode with
R
R
TEMP
TEMP
(5C)
(5C)
Ramp Rate = 48
Ramp Rate = 8
PWM CYCLE (%)
TIME (s)
TIME (s)
PWM DUTY CYCLE (%)
4.4
0.76
http://onsemi.com
120
100
80
60
40
20
0
140
120
100
80
60
40
20
0
51
of 2. In this instance, the fan takes about 17.6 seconds to
reach full running speed.
temperature with the slowest ramp rate. The ramp rate is set
to 1, while all other control parameters remain the same.
With the slowest ramp rate selected, it takes 35 seconds for
the fan to reach full speed.
reacts to temperature change is dependent on the ramp rate
selected in the enhanced acoustics registers. The higher the
ramp rate, the faster the fan reaches the newly calculated fan
speed.
Figure 79 shows the PWM output response for a ramp rate
Figure 80 shows how the control loop reacts to
As Figure 77 to Figure 80 show, the rate at which the fan
140
120
100
120
100
80
60
40
20
80
60
40
20
0
0
0
0
Figure 79. Enhanced Acoustics Mode with
Figure 80. Enhanced Acoustics Mode with
R
R
TEMP
TEMP
(5C)
(5C)
Ramp Rate = 2
Ramp Rate = 1
TIME (s)
TIME (s)
PWM DUTY CYCLE (%)
PWM DUTY CYCLE (%)
17.6
35
120
100
80
60
40
20
0
140
120
100
80
60
40
20
0