MAX1619 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX1619

Remote/Local Temperature Sensor with Dual Alarm Outputs and SMBus Serial Interface

Maxim Integrated 

Remote/Local Temperature Sensor with Dual-

Alarm Outputs and SMBus Serial Interface

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 two’s

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

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

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

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

Alarm Threshold Registers

Two registers store ALERT threshold limits, with high-

temperature (THIGH) and low-temperature (TLOW) 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 THIGH

register is full scale (0111 1111, or +127°C). The POR

state of the TLOW register is 1100 1001 or -55°C.

Two additional alarm threshold registers control the

OVERT output (see OVERT Alarm Output section), TMAX

and THYST. The POR state of TMAX is +100°C, and

THYST is +95°C.

OVERT 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. OVERT’s 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 TMAX and won’t go high again until the

temperature drops below THYST. The power-up default

settings for TMAX and THYST (+100°C and +95°C,

respectively) allow the MAX1619 to be used in stand-

alone thermostat applications where connection to an

SMBus serial bus isn’t 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 VCC - 1V (typical) due to the diode current

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

isn’t 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.

Table 2. Data Format (Two’s Complement)

TEMP.

(°C)

+130.00

+127.00

+126.50

+126.00

+25.25

+0.50

+0.25

0.00

-0.25

-0.50

-0.75

-1.00

-25.00

-25.50

-54.75

-55.00

-65.00

-70.00

ROUNDED

TEMP.

(°C)

+127

+127

+127

+126

+25

+1

0

0

0

0

-1

-1

-25

-25

-55

-55

-65

-65

DIGITAL OUTPUT

DATA BITS

SIGN

MSB

LSB

0

111

1111

0

111

1111

0

111

1111

0

111

1110

0

001

1001

0

000

0001

0

000

0000

0

000

0000

0

000

0000

0

000

0000

1

111

1111

1

111

1111

1

110

0111

1

110

0111

1

100

1001

1

100

1001

1

011

1111

1

011

1111

+3V TO +5.5V

+12V

STBY VCC

SMBUS

SERIAL

INTERFACE

(TO HOST)

MAX1619

SMBCLK

SMBDATA

ALERT

DXP

2N3904

DXN

ADD0

OVERT

ADD1

GND

PGND

Figure 4. Fan Control Application

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