Rainbow-electronics MAX1619 Bedienungsanleitung PDF herunterladen (Seite 11)

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 (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°C, and

HYST

is +95°C.

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. 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 T

MAX

and won’t go high again until the

temperature drops below T

HYST

. The power-up default

settings for T

MAX

and T

HYST

(+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 V

- 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.

MAX1619

Remote/Local Temperature Sensor with Dual-

Alarm Outputs and SMBus Serial Interface

______________________________________________________________________________________ 11

DIGITAL OUTPUT

DATA BITS

0 111 1111+127+127.00

0 111 1111

0 111 1110+126+126.00

+127+126.50

0 001 1001

0 000 0001+1+0.50

0 000 0000

0 000 000000.00

ROUNDED

TEMP.

(°C)

TEMP.

(°C)

0+0.25

+25+25.25

0 000 0000

0 000 00000-0.50

1 111 1111

1 111 1111-1-1.00

-1-0.75

1 110 0111

1 110 0111-25-25.50

1 100 1001

1 100 1001-55-55.00

0-0.25

-55-54.75

-25-25.00

1 011 1111

1 011 1111-65-70.00

-65-65.00

Table 2. Data Format (Two’s Complement)

SIGN MSB LSB

0 111 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

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 19 20

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