O.S.

GND

8

3

4

LM75

C1

100 nF

+12V

+12V/300 mA

Fan Motor

R1

10k

R2

10k

Q2

NDP410A

series

Q1

2N3904

R3

10k

7

6

5

1

2

A0

A1

A2

SCL

SDA

Optional but

Recommended

Pull-up

In Stand-alone

Mode

LM75B, LM75C

SNIS153D – JULY 2009 – REVISED OCTOBER 2015

www.ti.com

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

including base stations, electronic test equipment, office electronics, personal computers, and any other system

where thermal management is critical to performance.

8.2 Typical Application

8.2.1 Simple Fan Controller, Interface Optional

When using the two-wire interface: program O.S. for active high and connect O.S. directly to Q2's gate.

Figure 12. Simple Fan Controller, Interface Optional

8.2.1.1 Design Requirements

The LM75 requires a positive supply voltage of 2.7 V to 5.5 V to be applied between +Vs and GND. For best

results, bypass capacitors of 100 nF and 10 µF are recommended. Pull-up resistors of 10 k

Ω are required on

SCL and SDA.

8.2.1.2 Detailed Design Procedure

Accessing the conversion result of the LM75 consists of writing an address byte followed by retrieving the

corresponding number of data bytes. The first data byte is the most significant byte with the most significant bit

first, permitting only as much data as necessary to be read to determine temperature condition. For instance, if

the first four bits of the temperature data indicates an overtemperature condition, the host processor could

immediately take action to remedy the excessive temperatures. At the end of a read, the LM75 can accept either

Acknowledge or No Acknowledge from the Master (No Acknowledge is typically used as a signal for the slave

that the Master has read its last byte). Temperature data is two's complement format and one LSB is equivalent

to 0.5°C.

18

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