Rainbow-electronics MAX6681 Bedienungsanleitung PDF herunterladen (Seite 10)

MAX6680/MAX6681

To ensure valid extended data, read extended resolu-

tion temperature data using one of the following

approaches:

1) Put the MAX6680/MAX6681 into standby mode by

setting bit 6 of the Configuration register to 1. Initiate

a one-shot conversion using Send Byte command

0Fh. When this conversion is complete, read the

contents of the temperature data registers.

2) If the MAX6680/MAX6681 are in run mode, read the

Status register. If a conversion is in progress, the

BUSY bit is set to 1. Wait for the conversion to com-

plete as indicated by the BUSY bit being set to zero,

then read the temperature data registers.

Diode Fault Alarm

There is a continuity fault detector at DXP that detects

an open circuit between DXP and DXN, or a DXP short

to V

, GND, or DXN. If an open or short circuit exists,

the External Temperature register is loaded with 1000

0000. Additionally, if the fault is an open circuit, bit 2

(OPEN) of the Status byte is set to 1 and the ALERT

condition is activated at the end of the conversion.

Immediately after power-on reset, the Status register

indicates that no fault is present until the end of the first

conversion.

Alarm Threshold Registers

Four registers store ALERT threshold values—one high-

temperature (T

HIGH

) and one low-temperature (T

LOW

)

either measured temperature equals or exceeds the

corresponding ALERT threshold value, the ALERT out-

put is asserted.

The POR state of both ALERT T

HIGH

registers is 0111

1111 or +127°C and the POR state of T

LOW

registers is

1100 1001 or -55°C.

Two additional registers, RWOE and RWOI, store

remote and local alarm threshold data information cor-

responding to the OVERT output (see the

OVERT

Overtemperature Alarm section).

ALERT

The ALERT output operates in two modes—the typical

interrupt mode and comparator mode. The INT_SEL

input determines the mode. When INT_SEL is connect-

ed to V

high, using a weak pullup resistor, or left

floating, the ALERT functions in the interrupt mode.

ALERT

Interrupt Mode

An ALERT interrupt occurs when the internal or external

temperature reading exceeds a high or low tempera-

ture limit (user programmed) or when the remote diode

is disconnected (for continuity fault detection). The

ALERT interrupt output signal is latched and can be

cleared only by either reading the Status register or by

successfully responding to an Alert Response address.

In both cases, the alert is cleared even if the fault con-

dition still exists, but is reasserted at the end of the next

conversion. The interrupt does not halt automatic con-

versions. The interrupt output pin is open drain so that

multiple devices can share a common interrupt line.

The interrupt rate never exceeds the conversion rate.

Comparator Mode

Connecting INT_SEL to ground operates the ALERT

output in comparator mode. In the comparator mode,

whenever the temperature of the remote or local temp

sensor goes outside the limits set by T

HIGH

or T

LOW

the ALERT output becomes inactive after the tempera-

±1°C Fail-Safe Remote/Local Temperature

Sensors with SMBus Interface

10 ______________________________________________________________________________________

TEMP (°C)

LEGACY MODE

DIGITAL OUTPUT

EXTENDED

RANGE

DIGITAL OUTPUT

127.00 0111 1111 0111 1111

25 0001 1001 0001 1001

1 0000 0001 0000 0001

0.00 0000 0000 0000 0000

-1 0000 0000 1111 1111

-25 0000 0000 1110 0111

-64 0000 0000 1000 0000

Diode Fault

(Short or

Open)

1000 0000 1000 0000

Table 2. Data Format (Two’s Complement)

FRACTIONAL

TEMPERATURE

CONTENTS OF

EXTENDED REGISTER

0.000 000X XXXX

0.125 001X XXXX

0.250 010X XXXX

0.375 011X XXXX

0.500 100X XXXX

0.625 101X XXXX

0.750 110X XXXX

0.875 111X XXXX

Table 3. Extended Resolution Register

Note: Extended mode applies only for conversion rates of 4Hz

and slower.

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 16 17

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