TMP121

TMP123

SBOS273C − JUNE 2003 − REVISED FEBRUARY 2005

www.ti.com

5

APPLICATIONS INFORMATION

The TMP121 and TMP123 are 12-bit plus sign read-only

digital

temperature

sensors

optimal

for

thermal

management and thermal protection applications. The

TMP121 and the TMP123 communicate through a serial

interface that is SPI-compatible. Temperature is converted

to a 12-bit plus sign data word with 0.0625

°C resolution.

The TMP121 and TMP123 are specified for a temperature

range of −40

°C to +125°C, with operation extending from

−55

°C to +150°C.

The TMP121 and TMP123 are optimal for low power

applications, with a 0.5s conversion period for reduced

power consumption. The TMP121 and TMP123 are

specified for a supply voltage range of 2.7V to 5.5V, and

also feature a hardware shutdown to provide additional

power savings.

The

TMP121

and

TMP123

require

no

external

components for operation, though a 0.1

µF supply bypass

capacitor is recommended. Figure 1 shows typical

connections for the TMP121 and TMP123.

TMP121

0.1

µF

V+

GND

2

5

1

3

CS

4

6

SCK

SO

TMP123

0.1

µF

V+

GND

1

5

2

3

CS

NC = No Connection

4

6

SCK

SO

NOTE: (1) Pins labeled NC should be left floating or connected to GND.

Figure 1. Typical Connections of the TMP121 and

TMP123

The sensing device of both the TMP121 and TMP123 is

the chip itself; the die flag of the lead frame is thermally

connected to pin 2 of the TMP121, and of the TMP123.

Thermal paths run through the package leads as well as

the plastic package, and the lower thermal resistance of

metal causes the leads to provide the primary thermal

path. The GND pin (pin 2) of the TMP121 and the NC pin

(pin 2) of the TMP123 are thermally connected to the metal

lead frame, and are the best choice for thermal input.

To maintain accuracy in applications requiring air or

surface temperature measurement, care should be taken

to isolate the package and leads from ambient air

temperature.

TEMPERATURE REGISTER

The Temperature Register of the TMP121 and TMP123 is

a 16-bit, signed read-only register that stores the output of

the most recent conversion. Up to 16 bits can be read to

obtain data and are described in Table 1. The first 13 bits

are used to indicate temperature with bits D2 = 0, and D1,

D0 in a high impedance state. Data format for temperature

is summarized in Table 2. Following power-up or reset, the

Temperature Register will read 0

°C until the first

conversion is complete.

D15

D14

D13

D12

D11

D10

D9

D8

T12

T11

T10

T9

T8

T7

T6

T5

D7

D6

D5

D4

D3

D2

D1

D0

T4

T3

T2

T1

T0

0

Z

Z

Table 1. Temperature Register

TEMPERATURE

(

°C)

DIGITAL OUTPUT(1)

(BINARY)

HEX

150

0100 1011 0000 0000

4B00

125

0011 1110 1000 0000

3E80

25

0000 1100 1000 0000

0C80

0.0625

0000 0000 0000 1000

0008

0

0000 0000 0000 0000

0000

−0.0625

1111 1111 1111 1000

FFF8

−25

1111 0011 1000 0000

F380

−55

1110 0100 1000 0000

E480

(1) The last two bits are high impedance and are shown as 00 in the

table.

Table 2. Temperature Data Format

COMMUNICATING WITH THE TMP121

The

TMP121

and

TMP123

continuously

convert

temperatures to digital data while CS is high. CS must be

high for a minimum of one conversion time (320ms max)

to update the temperature data. Reading temperature data

from the TMP121 and TMP123 is initiated by pulling CS

low, which will cause any conversion in progress to

terminate, and place the device into analog shutdown.

Quiescent current is reduced to 1

µA during analog

shutdown. Once CS is pulled low, temperature data from

the last completed conversion prior to dropping CS is

latched into the shift register and clocked out at SO on the

falling SCK edge. The 16-bit data word is clocked out sign

bit first, followed by the MSB. Any portion of the 16-bit word

can be read before raising CS. The TMP121 and TMP123

typically require 0.25s to complete a conversion and

consume 50

µA of current during this period. If CS is held

high for longer than one conversion time period the

TMP121 and TMP123 will go into idle mode for 0.25s,

requiring only 20

µA of current. A new conversion begins

every 0.5s. Figure 2 describes the conversion timing for

the TMP121 and TMP123.