ADT7475ARQZ ON Semiconductor, ADT7475ARQZ Datasheet - Page 22

• Manufacturer Part Number: ADT7475ARQZ
• Description: IC REMOTE THERMAL CTRLR 16-QSOP
• Manufacturer: ON Semiconductor
• Series: dBCool®r

Specifications of ADT7475ARQZ

• 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
• Full Temp Accuracy: +/- 0.5 C
• Digital Output - Bus Interface: Serial (3-Wire, 4-Wire)
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

voltage applied across the fan and, therefore, the maximum
operating speed of the fan.
control.
signal. This assumes that the TACH signal is an
open−collector from the fan. In all cases, the TACH signal
from the fan must be kept below 3.6 V maximum to prevent
damaging the ADT7475. If in doubt as to whether the fan
used has an open−collector or totem pole TACH output, use
one of the input signal conditioning circuits shown in the Fan
Speed Measurement section.
transistor such as a general−purpose MMBT2222. While
these devices are inexpensive, they tend to have much lower
current handling capabilities and higher on resistance than
MOSFETs. When choosing a transistor, care should be taken
to ensure that it meets the fan’s current requirements.
is saturated when the fan is powered on.
speed is not switched on or off as with previous PWM
driven/powered fans. This enables it to perform better than
3−wire fans, especially for high frequency applications.
Figure 32 shows a typical drive circuit for 4−wire fans.
Figure 30. Driving a 3−Wire Fan Using an N−Channel
Figure 30 shows how to drive a 3−wire fan using PWM
Figure 30 uses a 10 kW pullup resistor for the TACH
Figure 31 shows a fan drive circuit using an NPN
Ensure that the base resistor is chosen so that the transistor
Because 4−wire fans are powered continuously, the fan
Figure 31. Driving a 3−Wire Fan Using an NPN
ADT7475
ADT7475
TACH
TACH
PWM
PWM
4.7kΩ
10kΩ
4.7kΩ
665Ω
Transistor
10kΩ
MOSFET
10kΩ
3.3V
3.3V
10kΩ
10kΩ
TACH
12V
12V
12V
12V
Q1
NDT3055L
Q1
MMBT2222
12V
FAN
12V
FAN
1N4148
1N4148
http://onsemi.com
22
Driving Two Fans from PWM3
speed measurement but only three PWM drive outputs. If a
fourth fan is used in the system, it should be driven from the
PWM3 output in parallel with the third fan. Figure 33 shows
how to drive two fans in parallel using low cost NPN
transistors. Figure 34 shows the equivalent circuit using a
MOSFET.
a matter of connecting another fan directly in parallel with
the first. Care should be taken in designing drive circuits
with transistors and FETs to ensure that the PWM pins are
not required to source current and that they sink less than the
8 mA maximum current specified on the data sheet.
The ADT7475 has four TACH inputs available for fan
Because the MOSFET can handle up to 3.5 A, it is simply
ADT7475
PWM3 Output Using a Single N−Channel MOSFET
ADT7475
Figure 33. Interfacing Two Fans in Parallel to the
Figure 34. Interfacing Two Fans in Parallel to the
PWM3 Output Using Low Cost NPN Transistors
TACH4
TACH3
PWM3
PWM3
ADT7475
Figure 32. Driving a 4−Wire Fan
3.3V
3.3V
3.3V
3.3V
1k
10kΩ
TYPICAL
10kΩ
TYPICAL
10kΩ
TYPICAL
2.2k
TACH
PWM
TACH
3.3V
TACH3
Q1
MMBT3904
4.7kΩ
+V
10
10
2kΩ
10kΩ
Q1
NDT3055L
3.3V
10kΩ
5V OR
12V FAN
TACH
12V
Q2
MMBT2222
12V
MMBT2222
1N4148
12V, 4−WIRE FAN
V
TACH
PWM
CC
TACH
Q3
12V
+V
5V OR
12V FAN
TACH4