MAX1619MEE+【PDF 11/20 页】IC TEMP SENSOR W/ALARM 16-QSOP

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tems, since a second master could overwrite the com-

mand byte without informing the first master.

The temperature data format is 7 bits plus sign in twos

complement form for each channel, with each data bit rep-

resenting 1癈 (Table 2), transmitted MSB first. Measure-

ments are offset by +1/2癈 to minimize internal rounding

errors; for example, +99.6癈 is reported as +100癈.

Alarm Threshold Registers

Two registers store ALERT threshold limits, with high-

temperature (T

HIGH

) and low-temperature (T

LOW

) reg-

isters for the remote A/D channel. There are no

comparison registers for the local A/D channel. If either

measured temperature equals or exceeds the corre-

sponding alarm threshold value, an ALERT interrupt is

asserted. The power-on-reset (POR) state of the T

HIGH

state of the T

LOW

Two additional alarm threshold registers control the

OVERT output (see OVERT Alarm Output section), T

MAX

and T

HYST

. The POR state of T

MAX

is +100癈, and

HYST

is +95癈.

OOVVEERRTT Alarm Output for Fan Control

The OVERT output is an unlatched open-drain output that

behaves as a thermostat to control a fan (Figure 4). When

using the SMBus interface, the polarity of the OVERT pin

(active-low at POR) can be inverted via bit 5 in the config-

uration byte. OVERTs current state can be read in the

status byte.

OVERT can also be used to control a fan without system

intervention. OVERT goes low when the remote tempera-

ture rises above T

MAX

and wont go high again until the

temperature drops below T

HYST

. The power-up default

settings for T

MAX

and T

HYST

(+100癈 and +95癈,

respectively) allow the MAX1619 to be used in stand-

alone thermostat applications where connection to an

SMBus serial bus isnt required.

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.

Remote/Local Temperature Sensor with Dual-

Alarm Outputs and SMBus Serial Interface

______________________________________________________________________________________ 11

DIGITAL OUTPUT

DATA BITS

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

ROUNDED

TEMP.

(癈)

TEMP.

(癈)

+0.25

+25

+25.25

000

0000

000

0000

-0.50

111

1111

111

1111

-1

-1.00

-1

-0.75

110

0111

110

0111

-25

-25.50

100

1001

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)

SIGN

MSB

LSB

111

1111

+127

+130.00

MAX1619

SMBCLK

ADD0

ADD1

STBY V

PGND

+12V

GND

DXP

DXN

+3V TO +5.5V

SMBUS

SERIAL

INTERFACE

(TO HOST)

2N3904

SMBDATA

ALERT

OVERT

Figure 4. Fan Control Application

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