Detailed Description

The LM75 temperature sensor measures temperature

and converts the data into digital form using a band-

gap type temperature sensor and a 9-bit sigma-delta

access to conversion results. The LM75 accepts stan-

perature alarm (OS) trip thresholds, and configure other

characteristics. While reading the Temperature register,

any changes in temperature are ignored until the read

is completed. The Temperature register is updated for

the new temperature measurement upon completion of

the read operation.

In comparator mode (see Figure 1), the open-drain OS

output asserts when the temperature rises above the

high impedance when the temperature falls below the

operates as a thermostat, and the OS output can be

used to take action to reduce the temperature (e.g.,

turn on a cooling fan, reduce clock speed, or shut

down the system).

remains asserted until a read operation is performed on

any of the registers. Once OS has asserted due to

The output then remains asserted until it is reset by a

read. It is then asserted again if the temperature rises

mode also resets OS.

Power-Up and Power-Down

The LM75 powers up to a known state, as indicated in

Table 2. Some of these settings are summarized as fol-

lowing:

• Comparator mode

• OS active low

• Command byte pointer = 0x00

From a software perspective, the LM75 appears as a set

of byte-wide registers that contain temperature data,

compatible, 2-wire serial interface reads temperature

data and writes control bits and alarm threshold data.

which is selected using A0, A1, and A2. See Table 1.

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

_______________________________________________________________________________________

5

OS OUTPUT

(COMPARATOR MODE)

OS SET ACTIVE LOW

OS OUTPUT

(INTERRUPT MODE)

OS SET ACTIVE LOW

READ

OPERATION

READ

OPERATION

READ

OPERATION

TEMPERATURE

Figure 1. OS Output Temperature Response Diagram

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

1

0

0

1

A2A1A0

RD/

W

Table 1. Slave Address

REGISTER NAME

ADDRESS

(hex)

POR STATE

(hex)

POR STATE (binary)

POR STATE (°C)

READ/

WRITE

Temperature

00

000X

0000 0000 0XXX XXXX

—

Read only

Configuration

01

00

0000 0000

—

R/W

02

4B0X

0100 1011 0XXX XXXX

75

R/W

03

500X

0101 0000 0XXX XXXX

80

R/W

Table 2. Register Functions

X

= Don’t care.