ADT7460ARQZ ON Semiconductor, ADT7460ARQZ Datasheet - Page 27

• Manufacturer Part Number: ADT7460ARQZ
• Description: IC REMOTE THRML/FAN CTRLR 16QSOP
• Manufacturer: ON Semiconductor
• Series: dBCool®r

Specifications of ADT7460ARQZ

• Function: Fan Control, Temp Monitor
• Topology: ADC, Comparator, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 120°C, External Sensor
• Output Type: SMBus™
• Output Alarm: No
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 120°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Full Temp Accuracy: +/- 3 C
• Digital Output - Bus Interface: Serial (3-Wire)
• Maximum Operating Temperature: + 120 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Fan Pulses per Revolution
pulses per revolution. Once the number of fan TACH pulses
is determined, it can be programmed into the fan pulses per
revolution register (Reg. 0x7B) for each fan. Alternatively,
this register can be used to determine the number of
pulses/revolution output by a given fan. By plotting fan
speed measurements at 100% speed with different
pulses/revolution settings, the smoothest graph with the
lowest ripple determines the correct pulses/revolution
value.
2−Wire Fan Speed Measurements
2−wire fans, that is, fans without TACH outputs. To do this,
the fan must be interfaced as shown in the Fan Drive
Circuitry section. In this case, the TACH inputs need to be
reprogrammed as analog inputs, AIN.
AIN Switching Threshold
2−wire measurements, the user can select the sensing
threshold for the AIN signal.
Table 29. Fan Pulses/Revolution Register (Reg. 0x7B)
Table 30. Fan Pulses/Revolution Register Bit Values
Table 31. Configuration Register 2 (Reg. 0x73)
Bit
<1:0>
<3:2>
<5:4>
<7:6>
Different fan models can output either 1, 2, 3, or 4 TACH
The ADT7460 is capable of measuring the speed of
Having configured the TACH inputs as AIN inputs for
3
2
1
0
Bit
Mnemonic
Value
AIN4
AIN3
AIN2
AIN1
00
01
10
11
FAN1 Default
FAN2 Default
FAN3 Default
FAN4 Default
Mnemonic
1 indicates that Pin 9 is reconfigured to
measure the speed of a 2−wire fan
using an external sensing resistor and
coupling capacitor.
1 indicates that Pin 4 is reconfigured to
measure the speed of a 2−wire fan
using an external sensing resistor and
coupling capacitor.
1 indicates that Pin 7 is reconfigured to
measure the speed of a 2−wire fan
using an external sensing resistor and
coupling capacitor.
1 indicates that Pin 6 is reconfigured to
measure the speed of a 2−wire fan
using an external sensing resistor and
coupling capacitor.
2 pulses per revolution
3 pulses per revolution
4 pulses per revolution
1 pulse per revolution
2 pulses per revolution
2 pulses per revolution
2 pulses per revolution
2 pulses per revolution
Description
Description
Description
http://onsemi.com
ADT7460
27
Fan Spin−Up
the fan at 100% PWM duty cycle until two TACH pulses are
detected on the TACH input. Once two pulses are detected,
the PWM duty cycle goes to the expected running value, for
example, 33%. The advantage of this is that fans have
different spin−up characteristics and take different amounts
of time to overcome inertia. The ADT7460 runs the fans just
fast enough to overcome inertia and is quieter on spin−up
than fans programmed to spinup for a given spin−up time.
Fan Startup Timeout
up (since it is below running speed), the ADT7460 includes
a fan startup timeout function. This is the time limit allowed
for two TACH pulses to be detected on spin−up. For
example, if 2 seconds fan startup timeout is chosen and no
TACH pulses occur within 2 seconds of the start of spin−up,
a fan fault is detected and flagged in the interrupt status
registers.
Disabling Fan Startup Timeout
than fixed−time spin−ups, the option exists to use fixed
spin−up times. Bit 5 (FSPDIS) = 1 in Configuration Register
1 (Reg. 0x40) disables the spin−up for two TACH pulses.
Instead, the fan spins up for the fixed time as selected in
Registers 0x5C to 0x5E.
PWM Logic State
duty cycle (non−inverted) or low for 100% duty cycle
(inverted).
Table 32. Configuration Register 4 (Reg. 0x7D)
Table 33. PWM1 to PWM3 Configuration
(Reg. 0x5C to 0x5E)
<3:2>
<2:0>
The ADT7460 has a unique fan spin−up function. It spins
To prevent false interrupts being generated as a fan spins
Although fan startup makes fan spin−ups much quieter
The PWM outputs can be programmed high for 100%
Bit
Bit
Mnemonic
Mnemonic
SPIN
AINL
These two bits define the input
threshold for 2−wire fan speed
measurements.
00 = ±20 mV
01 = ±40 mV
10 = ±80 mV
11 = ±130 mV
These bits control the startup
timeout for PWM1.
000 = no startup timeout
001 = 100 ms
010 = 250 ms (default)
011 = 400 ms
100 = 667 ms
101 = 1 s
110 = 2 s
111 = 4 s
Description
Description