LM73 datasheet(9/18 Pages) NSC

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1.0 Functional Description (Continued)

13-bit (12-bit plus sign)

Temperature

Digital Output

Binary

Hex

+150˚C

0100 1011 0000 0000

4B00h

+25˚C

0000 1100 1000 0000

0C80h

+1˚C

0000 0000 1000 0000

0080h

+0.0625˚C

0000 0000 0000 1000

0008h

0˚C

0000 0000 0000 0000

0000h

−0.0625˚C

1111 1111 1111 1000

FFF8h

−1˚C

1111 1111 1000 0000

FF80h

−25˚C

1111 0011 1000 0000

F380h

−40˚C

1110 1100 0000 0000

EC00h

14-bit (13-bit plus sign)

Temperature

Digital Output

Binary

Hex

+150˚C

0100 1011 0000 0000

4B00h

+25˚C

0000 1100 1000 0000

0C80h

+1˚C

0000 0000 1000 0000

0080h

+0.03125˚C

0000 0000 0000 0100

0004h

0˚C

0000 0000 0000 0000

0000h

−0.03125˚C

1111 1111 1111 1100

FFFCh

−1˚C

1111 1111 1000 0000

FF80h

−25˚C

1111 0011 1000 0000

F380h

−40˚C

1110 1100 0000 0000

EC00h

1.4 SMBus INTERFACE

The LM73 operates as a slave on the SMBus. The SMBDAT

line is bidirectional. The SMBCLK line is is an input only. The

LM73 never drives the SMBCLK line and it does not support

clock stretching.

The LM73 uses a 7-bit slave address. It is available in two

versions. Each version can be configured for one of three

unique slave addresses, for a total of six unique address.

Part Number

Address Pin

Device

Address

LM73-0

Float

Ground

1001 000

1001 001

1001 010

LM73-1

Float

Ground

1001 100

1001 101

1001 110

The SMBDAT output is an open-drain output and does not

have internal pull-ups. A “high” level will not be observed on

this pin until pull-up current is provided by some external

source, typically a pull-up resistor. Choice of resistor value

depends on many system factors but, in general, the pull-up

resistor should be as large as possible without effecting the

SMBus desired data rate. This will minimize any internal

temperature reading errors due to internal heating of the

LM73.

The LM73 features an integrated low-pass filter on both the

SMBCLK and the SMBDAT line. These filters increase com-

munications reliability in noisy environments.

If either the SMBCLK or SMBDAT line is held low for a time

greater than t

TIMEOUT (see Logic Electrical Characteristics

for the value of t

TIMEOUT), the LM73 state machine will reset

to the SMBus idle state, releasing the data line. Once the

SMBDAT is released high, the master may initiate an SMBus

start.

1.5 ALERT FUNCTION

The ALERT output is an over-temperature indicator. At the

end of every temperature conversion, the measured tem-

perature is compared to the value in the T

HIGH Register. If

the measured temperature exceeds the value stored in

HIGH, the ALERT output goes active (see Figure Figure 1).

This over-temperature condition will also cause the ALRT-

_STAT bit in the Control/Status Register to change value

(this bit mirrors the logic level of the ALERT pin).

The ALERT pin and the ALRT_STAT bit are cleared when

any of the following occur:

The measured temperature falls below the value stored

in the T

LOW Register

A "1" is written to the ALERT Reset bit in the Configura-

tion Register

The master resets it through an SMBus Alert Response

Address (ARA) procedure

If ALERT has been cleared by the master writing a "1" to the

ALERT Reset bit, while the measured temperature still ex-

ceeds the T

HIGH setpoint, ALERT will go active again after

the completion of the next temperature conversion.

Each temperature reading is associated with a Temperature

High (THI) and a Temperature Low (TLOW) flag in the

Control/Status Register. A digital comparison determines

whether that reading is above the T

HIGH setpoint or below

the T

LOW setpoint. If so, the corresponding flag is set. All

digital comparisons to the T

HIGH, and TLOW values are based

on an 11-bit temperature comparison. Regardless of the

resolution setting of the LM73, the lower three temperature

LSBs will not affect the state of the ALERT output, THI flag,

and TLOW flag.

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