ADT7476ARQZ ON Semiconductor, ADT7476ARQZ Datasheet - Page 23

• Manufacturer Part Number: ADT7476ARQZ
• Description: IC REMOTE THERMAL CTRLR 24QSOP
• Manufacturer: ON Semiconductor
• Series: dBCool®r

Specifications of ADT7476ARQZ

• 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: 24-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

Interrupt Mask Register 2 (0x75)
Bit 7 (D2) = 1, masks SMBALERT for Diode 2 errors.
Bit 6 (D1) = 1, masks SMBALERT for Diode 1 errors.
Bit 5 (FAN4) = 1, masks SMBALERT for Fan 4 failure.
bit masks SMBALERT for a THERM event. If the TACH4
pin is being used as GPIO6, setting this bit masks interrupts
related to GPIO6.
Bit 4 (FAN3) = 1, masks SMBALERT for Fan 3.
Bit 3 (FAN2) = 1, masks SMBALERT for Fan 2.
Bit 2 (FAN1) = 1, masks SMBALERT for Fan 1.
Bit 1 (OVT) = 1, masks SMBALERT for overtemperature
(exceeding THERM temperature limits).
Bit 0 (12 V/VC) = 1, masks SMBALERT for 12 V channel
or for a VID code change, depending on the function used.
Enabling the SMBALERT Interrupt Output
default. Pin 10 or Pin 14 can be reconfigured as an
SMBALERT output to signal out−of−limit conditions.
Assigning THERM Functionality to a Pin
SMBALERT, THERM, GPIO6, and TACH4. The user
chooses the required functionality by setting Bit 0 and Bit 1
of Configuration Register 4 (0x7D).
If THERM is enabled on Bit 1, Configuration Register 3
(0x78):
•
•
If THERM is not enabled:
•
•
THERM as an Input
assertions on the THERM pin. This can be useful for
Table 11. Configuring Pin 10 as SMBALERT Output
Table 12. Configuring Pin 14
Configuration Register 3
(0x78)
If the TACH4 pin is being used as the THERM input, this
The SMBALERT interrupt function is disabled by
Pin 14 on the ADT7476 has four possible functions:
When THERM is configured as an input, the user can time
Pin 22 becomes THERM.
If Pin 14 is configured as THERM on Bit 0 and Bit 1 of
Configuration Register 4 (0x7D), THERM is enabled
on this pin.
Pin 22 becomes a 2.5 V measurement input.
If Pin 14 is configured as THERM, then THERM is
disabled on this pin.
Bit 1
0
0
1
1
Register
Bit 0
0
1
0
1
[1] Pin 10 = SMBALERT
[0] Pin 10 = PWM2
Bit Setting
SMBALERT
Function
THERM
TACH4
GPIO6
http://onsemi.com
23
connecting to the PROCHOT output of a CPU to gauge
system performance.
can also set up the ADT7476 to run the fans at 100%. The
fans run at 100% for the duration of time that the THERM
pin is pulled low. This is done by setting the BOOST bit
(Bit 2) in Configuration Register 3 (0x78) to 1. This works
only if the fan is already running, for example, in manual
mode, when the current duty cycle is above 0x00, or in
automatic mode when the temperature is above T
manual mode is set to 0x00, pulling the THERM low
externally has no effect. See Figure 31 for more information.
THERM Timer
assertion time. For example, the THERM input can be
connected to the PROCHOT output of a Pentium 4 CPU to
measure system performance. The THERM input can also
be connected to the output of a trip−point temperature
sensor.
THERM input and stopped when THERM is de−asserted.
The timer counts THERM times cumulatively; that is, the
timer resumes counting on the next THERM assertion. The
THERM timer continues to accumulate THERM assertion
times until the timer is read (where it is cleared), or until it
reaches full scale. If the counter reaches full scale, it stops
at that reading until cleared.
so that Bit 0 is set to 1 on the first THERM assertion. Once
the cumulative THERM assertion time has exceeded
45.52 ms, Bit 1 of the THERM timer is set and Bit 0 now
becomes the LSB of the timer with a resolution of 22.76 ms
(see Figure 32).
T
THERM
THERM ASSERTED TO LOW AS AN INPUT:
FANS DO NOT GO TO 100% BECAUSE
TEMPERATURE IS BELOW T
MIN
When the THERM pin is driven low externally, the user
If the temperature is below T
The ADT7476 has an internal timer to measure THERM
The timer is started on the assertion of the ADT7476’s
The 8−bit THERM timer status register (0x79) is designed
Figure 31. Asserting THERM Low as an Input in
Automatic Fan Speed Control Mode
THERM ASSERTED TO LOW AS AN INPUT:
FANS GO TO 100% BECAUSE TEMPERATURE
IS ABOVE T
MIN
MIN
.
AND FANS ARE ALREADY RUNNING.
MIN
or if the duty cycle in
MIN
.