MAX1617MEE+T【PDF 11/20 页】IC REMOTE/LOCAL TEMP SNSR 16QSOP

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Sheet目录42

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Remote/Local Temperature Sensor

with SMBus Serial Interface

MAX1617

Maxim Integrated

Alarm Threshold Registers

Four registers store alarm threshold data, with high-

temperature (T

HIGH

) and low-temperature (T

LOW

) reg-

isters for each A/D channel. If either measured

temperature equals or exceeds the corresponding

alarm threshold value, an ALERT interrupt is asserted.

The power-on-reset (POR) state of both T

HIGH

registers

is full scale (0111 1111, or +127癈). The POR state of

both T

LOW

registers is 1100 1001 or -55癈.

Diode Fault Alarm

There is a continuity fault detector at DXP that detects

whether the remote diode has an open-circuit condi-

tion. At the beginning of each conversion, the diode

fault is checked, and the status byte is updated. This

fault detector is a simple voltage detector; if DXP rises

above V

- 1V (typical) due to the diode current

source, a fault is detected. Note that the diode fault

isnt checked until a conversion is initiated, so immedi-

ately after power-on reset the status byte indicates no

fault is present, even if the diode path is broken.

If the remote channel is shorted (DXP to DXN or DXP to

GND), the ADC reads 0000 0000 so as not to trip either

the T

HIGH

or T

LOW

alarms at their POR settings. In

applications that are never subjected to 0癈 in normal

operation, a 0000 0000 result can be checked to indi-

cate a fault condition in which DXP is accidentally short

circuited. Similarly, if DXP is short circuited to V

, the

ADC reads +127癈 for both remote and local channels,

and the device alarms.

AALLEERRTT Interrupts

The ALERT interrupt output signal is latched and can

only be cleared by reading the Alert Response address.

Interrupts are generated in response to T

HIGH

and T

LOW

comparisons and when the remote diode is disconnect-

ed (for continuity fault detection). The interrupt does not

halt automatic conversions; new temperature data con-

tinues to be available over the SMBus interface after

ALERT is asserted. The interrupt output pin is open-drain

so that devices can share a common interrupt line. The

interrupt rate can never exceed the conversion rate.

The interface responds to the SMBus Alert Response

address, an interrupt pointer return-address feature

(see Alert Response Address section). Prior to taking

corrective action, always check to ensure that an inter-

rupt is valid by reading the current temperature.

Alert Response Address

The SMBus Alert Response interrupt pointer provides

quick fault identification for simple slave devices that

lack the complex, expensive logic needed to be a bus

master. Upon receiving an ALERT interrupt signal, the

host master can broadcast a Receive Byte transmission

to the Alert Response slave address (0001 100). Then

any slave device that generated an interrupt attempts

to identify itself by putting its own address on the bus

(Table 3).

111

1111

DIGITAL OUTPUT

DATA BITS

SIGN

MSB

LSB

111

1111

+127

+127.00

111

1111

111

1110

+126

+126.00

+127

+126.50

001

1001

000

0001

+0.50

000

0000

000

0000

+0.00

+127

+130.00

+0.25

+25

+25.25

000

0000

000

0000

-0.50

111

1111

111

1111

-1

-1.00

TEMP.

(癈)

-1

-0.75

110

0111

110

0110

-25

-25.50

100

1001

ROUNDED

TEMP.

(癈)

100

1001

-55

-55.00

-0.25

-55

-54.75

-25

-25.00

011

1111

011

1111

-65

-70.00

-65

-65.00

Table 2. Data Format (Twos-Complement)

Table 3. Read Format for Alert Response

Address (0001100)

ADD6

Provide the current MAX1617

slave address that was latched at

POR (Table 8)

FUNCTION

ADD5

ADD4

ADD3

ADD2

ADD1

ADD7

(MSB)

(LSB)

Logic 1

BIT

NAME

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