TMP125

SBOS323A − DECEMBER 2004 − REVISED JUNE 2005

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5

APPLICATIONS

The TMP125 10-bit, read-only digital temperature sensor

is optimal for thermal management and thermal protection

applications. The TMP125 is specified for a temperature

range of −40

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

to −55

°C. It is specified for a supply voltage range of 2.7V

to 5.5V, and also features a hardware shutdown to provide

power savings. Quiescent current is reduced to 1

µA during

analog shutdown.

The TMP125 communicates through a serial interface that

is SPI-compatible. Temperature is converted to a 10-bit

data word with 0.25

°C resolution. The TMP125 is optimal

for low-power applications, with a 120ms conversion

period for reduced power consumption.

The sensing device of the TMP125 is the chip itself.

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 TMP125 requires no external components for

operation, though a 0.1

µF supply bypass capacitor is

recommended. Figure 1 shows typical connection for the

TMP125.

TMP125

0.1

µF

V+

1

5

2

3

CS

SI

4

6

SCK

SO

Figure 1. Typical Connections for the TMP125

COMMUNICATING WITH THE TMP125

The TMP125 continuously converts temperatures to

digital data. Temperature data is read by pulling CS low.

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. The SI pin is used to put the device

into shutdown mode. To enter shutdown mode, SI must be

high on the rising edge of the third bit of SCK (see

Figure 3). Also, all 16 bits must be clocked to allow

shutdown on the TMP125. To bring the device out of

shutdown, perform a 16-clock communication with SI set

to logic low. The 16-clock communication is the same as

the Data Read shown in Figure 3, except that the data on

SO will be the last conversion prior to putting the device

into shutdown mode. Note that SO is only used to control

the shutdown function; if not using this function, connect

this pin to ground.

The one-shot command can be used to force a single

conversion. When the command is issued, the part will

perform a single conversion and then go into shutdown

mode. After the conversion is complete, the conversion

result should be read with the power-down bit high (see

Figure 3) if you do not want to start a new conversion.

The TMP125 will go into idle mode for 60ms, requiring only

20

µA of current. A new conversion begins every 120ms.

Figure 2 describes the conversion timing for the TMP125.

TEMPERATURE REGISTER

The Temperature Register of the TMP125 is a 16-bit,

read-only register that stores the output of the most recent

conversion. However, temperature is represented by only

10-bits, which are in signed two’s complement format. The

first bit of the Temperature Register, D15, is a leading zero.

Bits D14 and D5 are used to indicate temperature. Bits D4

to D0 are the same as D5 (see Table 1). Data format for

temperature is summarized in Table 2. When calculating

the signed two’s complement temperature value, be sure

to use only the 10 data bits.

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

0

T9

T8

T7

T6

T5

T4

T3

D7

D6

D5

D4

D3

D2

D1

D0

T2

T1

T0

T0

T0

T0

T0

T0

Table 1. Temperature Register

TEMPERATURE

(

°C)

DIGITAL OUTPUT

D14

…D5

+127

01 1111 1100

+125

01 1111 0100

+100

01 1001 0000

+75

01 0010 1100

+50

00 1100 1000

+25

00 0110 0100

+10

00 0010 1000

+0.25

00 0000 0001

0

00 0000 0000

−0.25

11 1111 1111

−25

11 1001 1100

−50

11 0011 1000

−55

11 0010 0100

Table 2. Temperature Data Format