S

S

S

1

1

1

1

0

0

0

0

P0

D0

P1

D1

P2

D2

P3

D3

P4

D4

P5

D5

P6

D6

P7

D7

P

P

P

Calibration Byte (55h)

Command with Address Pointer

Register Data (8 LSBs)

S

P

= Start Condition of SMAART Wire Protocol

= Stop Condition of SMAART Wire Protocol

1-bit default delay

for bus direction change.

Driven by TMP104

TMP104

SBOS564A

– NOVEMBER 2011 – REVISED NOVEMBER 2011

www.ti.com

APPLICATION INFORMATION

GENERAL DESCRIPTION

The TMP104 is a digital output temperature sensor in a wafer chip-scale package (WCSP) that is optimal for

thermal management and thermal profiling. The TMP104 includes a SMAART wire interface that is capable of

communicating in a daisy-chain with up to 16 devices on a single bus. The interface requires two pins from the

host; the first device in the daisy-chain receives data from the host and the last device in the daisy-chain returns

data to the host. In addition, the TMP104 has the capability of executing multiple device access (MDA)

commands that allow multiple TMP104s to respond to a single global bus command. MDA commands reduce

communication time and power in a bus that contains multiple TMP104 devices. The TMP104 is specified over a

temperature range of

–40ºC to +125ºC.

The TMP104 also has the capability of configuring the bus in a transparent mode, where the input from the host

is sent directly to the next device in the chain without delay. Additionally, the TMP104 can disconnect the chain

and create a serial communication controlled by each TMP104 on the bus, thereby allowing each device to have

configurable addressing and interrupt capabilities. The input pin, RX, is a high-impedance node. The output pin,

TX, has an internal push-pull output stage that can drive the host to GND or V+.

After an initialization sequence, each device on the bus is programmed with its own interface address that allows

it to respond to its own address and also respond to general commands that permit the user to read or write to all

of the devices on the bus without having to send its individual address and command to each individual device.

The temperature sensor in the TMP104 is the chip itself. Thermal paths run through the package bumps as well

as the package. The lower thermal resistance of metal causes the bumps to provide the primary thermal path. To

maintain accuracy in applications that require air or surface temperature measurement, care should be taken to

isolate the package from ambient air temperature. A thermally-conductive adhesive can help to achieve accurate

surface temperature measurement.

COMMUNICATION PROTOCOL

Each communication of the SMAART wire protocol consists of 8-bit words, transferred least significant bit (LSB)

first. Each 8-bit word begins with a Start bit that is logic low, and ends with a Stop bit that is logic high. By using

a Start bit and Stop bit for each 8-bit word, the TMP104 can calibrate each word and maintain synchronous

communication throughout the process. The host commences the communication by sending a Start bit followed

by the calibration byte (55h), allowing the TMP104 to sync to the baud rate of the host, followed by the Stop bit.

Then, another Start bit is sent, followed by the command register byte and a Stop bit. Finally, a third Start bit is

sent followed by the data byte, where master sends data if the instruction is a write command, or the TMP104

breaks the chain and sends data if the instruction is a read command. The process finishes with a Stop bit. The

sequence is shown in Table 1 and Figure 5.

Table 1. Communication Format

Command

Data

Start bit

Calibration

Stop bit

Start bit

Stop bit

Start bit

Stop bit

byte

byte

Figure 5. Generic Communication BitStream

6

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© 2011, Texas Instruments Incorporated

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