ADT7476AARQZ-REEL ON Semiconductor, ADT7476AARQZ-REEL Datasheet - Page 21

• Manufacturer Part Number: ADT7476AARQZ-REEL
• Description: IC REMOTE THERMAL CTRLR 24-QSOP
• Manufacturer: ON Semiconductor
• Series: dBCool®r

Specifications of ADT7476AARQZ-REEL

• 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
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Fan Limit Registers
Register 0x54, TACH1 Minimum Low Byte = 0xFF default
Register 0x55, TACH1 Minimum High Byte = 0xFF default
Register 0x56, TACH2 Minimum Low Byte = 0xFF default
Register 0x57, TACH2 Minimum High Byte = 0xFF default
Register 0x58, TACH3 Minimum Low Byte = 0xFF default
Register 0x59, TACH3 Minimum High Byte = 0xFF default
Register 0x5A, TACH4 Minimum Low Byte = 0xFF default
Register 0x5B, TACH4 Minimum High Byte = 0xFF default
Out-of-Limit Comparisons
can be enabled for monitoring. The ADT7476A measures
all voltage and temperature measurements in round robin
format and sets the appropriate status bit for out-of-limit
conditions. TACH measurements are not part of this round
robin cycle. Comparisons are done differently depending on
whether the measured value is being compared to a high or
low limit.
comparator for error detecting and, therefore, have high and
low limits. Fan speed measurements use only a low limit.
This fan limit is needed only in manual fan control mode.
Analog Monitoring Cycle Time
the start bit (Bit 0) of Configuration Register 1 (0x40). The
ADC measures each analog input in turn, and, as each
measurement is completed, the result is automatically stored
in the appropriate value register. This round robin
monitoring cycle continues unless disabled by writing a 0 to
Bit 0 of Configuration Register 1.
time taken to monitor all the analog inputs is normally not
of interest, because the most recently measured value of any
input can be read out at any time.
important, it can easily be calculated.
The total number of channels measured is:
•
•
•
•
conversions and takes 11 ms for each voltage measurement,
12 ms for a local temperature reading, and 39 ms for each
remote temperature reading. The total monitoring cycle time
for averaged voltage and temperature monitoring is,
therefore, nominally
( 5
Once all limits have been programmed, the ADT7476A
Voltage and temperature channels use a window
The analog monitoring cycle begins when a 1 is written to
As the ADC is normally left to free-run in this manner, the
For applications where the monitoring cycle time is
As mentioned previously, the ADC performs round robin
Four dedicated supply voltage inputs
Supply voltage (V
Local temperature
Two remote temperatures
High Limit: > Comparison Performed
Low Limit: ≤ Comparison Performed
11 ) ) 12 ) ( 2
CC
pin)
39 ) + 145 ms
(eq. 3)
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21
synchronized with the analog measurements in any way.
Status Registers
Status Register 1 and Interrupt Status Register 2. The status
register bit for each channel reflects the status of the last
measurement and limit comparison on that channel. If a
measurement is within limits, the corresponding status
register bit is cleared to 0. If the measurement is out-of-limits,
the corresponding status register bit is set to 1.
polled by reading the status registers over the serial bus. In
Bit 7 (OOL) of Interrupt Status Register 1 (0x41), 1 means
an out-of-limit event has been flagged in Interrupt Status
Register 2. This means the user also needs to read Interrupt
Status Register 2. Alternatively, Pin 10 or Pin 14 can be
configured as an SMBALERT output. This hard interrupt
automatically notifies the system supervisor of an
out-of-limit condition. Reading the status registers clears the
appropriate status bit as long as the error condition that
caused the interrupt has cleared. Status register bits are
sticky. Whenever a status bit is set, indicating an out-of-limit
condition, it remains set even if the event that caused it has
gone away (until read).
register after the event has gone away. Interrupt mask
registers (0x74 and 0x75) allow individual interrupt sources
to be masked from causing an SMBALERT. However, if one
of these masked interrupt sources goes out of limit, its
associated status bit is set in the status registers.
Interrupt Status Register 1 (0x41)
Bit 7 (OOL) = 1, denotes a bit in Interrupt Status Register 2
is set and Interrupt Status Register 2 should be read.
Bit 6 (R2T) = 1, Remote 2 temperature high or low limit has
been exceeded.
Bit 5 (LT) = 1, Local temperature high or low limit has been
exceeded.
Bit 4 (R1T) = 1, Remote 1 temperature high or low limit has
been exceeded.
Bit 3 (5.0 V) = 1, 5.0 V high or low limit has been exceeded.
Bit 2 (V
Bit 1 (V
Bit 0 (2.5 V) = 1, 2.5 V high or low limit has been exceeded.
If the 2.5 V input is configured as THERM, this bit
represents the status of THERM.
Interrupt Status Register 2 (0x42)
Bit 7 (D2) = 1, indicates an open or short on D2+/D2– inputs.
Bit 6 (D1) = 1, indicates an open or short on D1+/D1– inputs.
Bit 5 (F4P) = 1, indicates Fan 4 has dropped below minimum
speed. Alternatively, indicates that the THERM limit has
Fan TACH measurements are made in parallel and are not
The results of limit comparisons are stored in Interrupt
The state of the various measurement channels can be
The only way to clear the status bit is to read the status
CCP
CC
) = 1, V
) = 1, V
CC
CCP
high or low limit has been exceeded.
high or low limit has been exceeded.