ADT7475 查看數據表（PDF） - ON Semiconductor

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ADT7475

dBCOOL® Remote Thermal Monitor and Fan Controller

ON Semiconductor 

ADT7475

actually being measured, exceeding the limit indicates a

slow or stalled fan.

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

Once all limits have been programmed, the ADT7475 can

be enabled for monitoring. The ADT7475 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.

High Limit > Comparison Performed

Low Limit ≤ Comparison Performed

Voltage and temperature channels use a window

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 analog monitoring cycle begins when a 1 is written to

the start bit (Bit 0) of Configuration Register 1 (0x40).

By default, the ADT7475 powers up with this bit set. 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.

As the ADC is normally left to free−run in this manner, the

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.

For applications where the monitoring cycle time is

important, it can easily be calculated. The total number of

channels measured is

• One dedicated supply voltage input (VCCP pin)

• Supply voltage (VCC pin)

• Local temperature

• Two remote temperatures

As mentioned previously, the ADC performs round−robin

conversions. The total monitoring cycle time for averaged

voltage and temperature monitoring is 146 ms. The total

monitoring cycle time for voltage and temperature

monitoring with averaging disabled is 19 ms. The ADT7475

is a derivative of the ADT7467. As a result, the total

conversion time in the ADT7475 is the same as the total

conversion time of the ADT7467.

Fan TACH measurements are made in parallel and are not

synchronized with the analog measurements in any way.

Interrupt Status Registers

The results of limit comparisons are stored in Interrupt

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.

The state of the various measurement channels can be

polled by reading the status registers over the serial bus. In

Bit 7 (OOL) of Interrupt Status Register 1 (0x41), 1 means

that an out−of−limit event has been flagged in Interrupt

Status Register 2. This means that the user needs only to read

Interrupt Status Register 2 when this bit is set. Alternatively,

Pin 5 or Pin 9 can be configured as an SMBALERT output.

This 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). The only

way to clear the status bit is to read the status register after

the event has gone away. Interrupt status 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 interrupt status registers.

Interrupt Status Register 1 (0x41)

Bit 7 (OOL) = 1, denotes that a bit in Status Register 2 is set

and that 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 2 (VCC) = 1, VCC high or low limit has been exceeded.

Bit 1 (VCCP) = 1, VCCP high or low limit has been exceeded.

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 that Fan 4 has dropped below

minimum speed. Alternatively, indicates that the THERM

limit has been exceeded, if the THERM function is used.

Bit 4 (FAN3) = 1, indicates that Fan 3 has dropped below

minimum speed.

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