ADT7462ACPZ-REEL7 ON Semiconductor, ADT7462ACPZ-REEL7 Datasheet - Page 28

• Manufacturer Part Number: ADT7462ACPZ-REEL7
• Description: IC TEMP/VOLT MONITOR 32-LFCSP
• Manufacturer: ON Semiconductor

Specifications of ADT7462ACPZ-REEL7

• Function: Fan Control, Temp Monitor
• Topology: ADC, Comparator, 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 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 32-LFCSP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Fan Speed Measurement and Control
TACH Inputs
are TACH inputs intended for fan speed measurement.
slow rise and fall times typical of fan tachometer outputs.
The maximum input signal range is 0 V to 5.0 V, even when
V
supplied from fan outputs that exceed 0 V to 5.0 V, either
resistive attenuation of the fan signal or diode clamping
must be included to keep inputs within an acceptable range.
TACH circuits.
be connected directly to the fan input, as shown in Figure 43.
voltage greater than 5.0 V), the fan output can be clamped
with a Zener diode, as shown in Figure 44. The Zener diode
voltage should be chosen so that it is greater than V
TACH input but less than 5.0 V, allowing for the voltage
tolerance of the Zener diode. A value of between 3.0 V and
5.0 V is suitable.
Figure 42. Interfacing Two Fans in Parallel to a PWM
CC
Pin 1, Pin 2, Pin 3, Pin 4, Pin 7, Pin 8, Pin 21, and Pin 22
Signal conditioning in the ADT7462 accommodates the
Figure 43 to Figure 46 show circuits for most common fan
If the fan TACH output has a resistive pullup to V
If the fan output has a resistive pullup to 12 V (or other
ADT7462
is less than 5.0 V. In the event that these inputs are
Output Using a Single N−Channel MOSFET
TACH7
TACH3
PWM3
Figure 43. Fan with TACH Pullup to V
12 V
3.3 V
3.3 V
TYPICAL
PULLUP
10 kΩ
TYPICAL
10 kΩ
TYPICAL
10 kΩ
TYPICAL
4.7 kΩ
3.3 V
TACH
+V
TACH
OUTPUT
Q1
NDT3055L
TACH
5.0V or
12 V FAN
1N4148
ADT7462
FAN SPEED
COUNTER
TACH
V
CC
CC
+V
CC
5.0 V or
12 V FAN
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http://onsemi.com
, it can
of the
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a totem−pole output, a series resistor can be added to limit
the Zener current, as shown in Figure 45. Alternatively, a
resistive attenuator can be used, as shown in Figure 46. R1
and R2 should be chosen such that:
160 kW to ground, so this should be taken into account when
calculating resistor values.
than 1 kW, suitable values for R1 and R2 would be 100 kW
and 47 kW. This gives a high input voltage of 3.83 V.
Fan Speed Measurement
fans differs from that used with 4−wire fans. When 3−wire
FAN
Figure 44. Fan with TACH Pullup to Voltage > 5.0 V,
If the fan has a strong pullup (less than 1 kW) to 12 V or
The fan inputs have an input resistance of nominally
With a pullup voltage of 12 V and a pullup resistor of less
The method of fan speed measurement when using 3−wire
Figure 45. Fan with Strong TACH Pullup to >V
Figure 46. Fan with Strong TACH Pullup to >V
2.0 V < V
or Totem−Pole Output, Attenuated with R1/R2
12 V
(Example 12 V) Clamped with Zener Diode
5.0 V or 12 V
12 V
TOTEM POLE
or Totem−Pole Output, Clamped with
PULLUP TYP
< 1 kΩ
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 y V
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 y V
< 1 kΩ
TYPICAL
PULLUP
PULLUP
4.7 kΩ
Zener Diode and Resistor
or
TACH
OUTPUT
TACH
OUTPUT
× R2/(R
10 kΩ
TACH
OUTPUT
R1*
R1
*SEE TEXT
PULLUP
ZD1
ZENER*
R2*
ZD1*
TACH
TACH
TACH
+ R1 + R2) < 5.0 V
ADT7462
ADT7462
FAN SPEED
FAN SPEED
ADT7462
FAN SPEED
COUNTER
COUNTER
COUNTER
V
V
V
CC
CC
CC
CC.
CC.
CC
CC