MAX1989MUE+【PDF 11/17 页】IC TEMP SENSOR REMOTE 16TSSOP

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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 (typ) due to the diode current source, a

fault is detected. Note that the diode fault is not

checked until a conversion is initiated, so immediately

after power-on reset, the status byte indicates no fault

is present, even if the diode path is broken.

If any 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 set-

tings. In applications that are never subjected to 0癈 in

normal operation, a 0000 0000 result can be checked

to indicate a fault condition in which DXP_ is acciden-

tally short circuited. Similarly, if DXP_ is short circuited

to V

, the ADC reads +127癈 for all 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 a remote diode is disconnected

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

automatic conversions; new temperature data continues

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).

The alert response can activate several different slave

devices simultaneously, similar to the I

C general call. If

more than one slave attempts to respond, bus arbitra-

tion rules apply, and the device with the lower address

code wins. The losing device does not generate an

acknowledge and continues to hold the ALERT line low

until serviced (implies that the host interrupt input is

Multichannel Remote/Local

Temperature Sensors

______________________________________________________________________________________ 11

Table 2. Data Format (Twos Complement)

Table 3. Read Format for Alert Response

Address (0001100)

ADD6

Provide the current

MAX1668/MAX1805/MAX1989

slave address that was latched at

POR (Table 8)

FUNCTION

ADD5

ADD4

ADD3

ADD2

ADD1

ADD7

(MSB)

(LSB)

Logic 1

BIT

NAME

DIGITAL OUTPUT DATA BITS

TEMP

(癈)

ROUNDED

TEMP

(癈)

SIGN

MSB

LSB

+130.00

+127

111

1111

+127.00

+127

111

1111

+126.50

+127

111

1111

+126.00

+126

111

1110

+25.25

+25

001

1001

+0.50

000

0000

+0.25

000

0000

+0.00

000

0000

-0.25

000

0000

-0.50

000

0000

-0.75

-1

111

1111

-1.00

-1

111

1111

-25.00

-25

110

0111

-25.50

-25

110

0110

-54.75

-55

100

1001

-55.00

-55

100

1001

-65.00

-65

011

1111

-70.00

-65

011

1111

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