TMP125 Datasheet, PDF (5/12 Pages) Texas Instruments – Accurate Digital Temperature Sensor with SPI Interface

TMP125
www.ti.com
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 1µA 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 0.1µF supply bypass capacitor is
recommended. Figure 1 shows typical connection for the
TMP125.
V+
SCK ₄
3
2
SO ₆ TMP125
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1
0.1µF
SI
CS
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
SBOS323A − DECEMBER 2004 − REVISED JUNE 2005
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
20µA 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
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