ADT7460ARQZ-RL7 ONSEMI [ON Semiconductor], ADT7460ARQZ-RL7 Datasheet - Page 25

• Manufacturer Part Number: ADT7460ARQZ-RL7
• Description: dBCOOL Remote Thermal Monitor and Fan Controller
• Manufacturer: ONSEMI [ON Semiconductor]

Laying Out 2−Wire and 3−Wire Fans
arrangement for 2−wire and 3−wire fans. Some components
are not populated, depending on whether a 2−wire or 3−wire
fan is used.
TACH Inputs
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 where
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 outputs.
CC
TACH/AIN
Figure 46 shows how to lay out a common circuit
Pins 4, 6, 7, and 9 are open−drain TACH inputs for fan
Signal conditioning in the ADT7460 accommodates the
Figure 47 to Figure 50 show circuits for most common fan
Figure 46. Planning for 2−Wire or 3−Wire Fans on a
is less than 5.0 V. In the event that these inputs are
CH1
CH3 50.0mV
Figure 45. Fan Speed Sensing Waveform at
100mV
R1
R2
R3
CH2 5.00mV
CH4 50.0mV
C1
12V OR 5.0V
TACH/AIN Pin
R4
PCB
Q1
MMBT2222
M 4.00ms
T
1N4148
ć1.00000ms
3.3V OR 5.0V
R5
FOR 3-WIRE FANS:
POPULATE R1, R2, R3 R4 = 0Ω
C1 = UNPOPULATED
FOR 2-WIRE FANS:
POPULATE R4, C1
R1, R2, R3 UNPOPULATED
A CH1
PWM
@: –258mV
n: 250 mV
–2.00mV
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ADT7460
25
be connected directly to the fan input, as shown in Figure 47.
voltage greater than 5.0 V), the fan output can be clamped
with a Zener diode, as shown in Figure 48. The Zener diode
voltage should be greater than V
less than 5.0 V, allowing for the voltage tolerance of the
Zener. A value of between 3 V and 5.0 V is suitable.
a totem−pole output, a series resistor can be added to limit
the Zener current, as shown in Figure 49. Alternatively, a
resistive attenuator may be used, as shown in Figure 50. R1
and R2 should be chosen such that:
160 kW to ground. This should be taken into account when
calculating resistor values.
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.
Totem−Pole Output, Clamped with Zener and Resistor
5.0V OR 12V
If the fan TACH output has a resistive pullup to V
If the fan output has a resistive pullup to 12 V (or other
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 pullup resistor less than
Figure 49. Fan with Strong TACH Pullup to > V
Figure 48. Fan with TACH Pullup to Voltage . 5.0 V,
FAN
2 V < V
for Example, 12 V, Clamped with Zener Diode
12V
Figure 47. Fan with TACH Pullup to V
12V
TOTEM POLE
PULLUP TYP
PULLUP
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 y V
<1kΩ OR
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 y V
TYPICAL
TYPICAL
PULLUP
PULLUP
4.7kΩ
4.7kΩ
× R2/(R
TACH
OUTPUT
TACH
OUTPUT
TACH
OUTPUT
PULLUP
TACH
ZD1
ZENER*
IH
ZD1*
TACH
TACH
of the TACH input but
+ R1 + R2) < 5.0 V
ADT7460
FAN SPEED
COUNTER
V
ADT7460
FAN SPEED
ADT7460
FAN SPEED
COUNTER
CC
COUNTER
V
V
CC
CC
CC
CC
CC
CC
CC
, it can
or