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TMP05/TMP06

Rev. 0 | Page 17 of 28

APPLICATION HINTS

THERMAL RESPONSE TIME

The time required for a temperature sensor to settle to a

specified accuracy is a function of the thermal mass of the

sensor and the thermal conductivity between the sensor and the

object being sensed. Thermal mass is often considered

equivalent to capacitance. Thermal conductivity is commonly

specified using the symbol Q, and can be thought of as thermal

resistance. It is commonly specified in units of degrees per watt

of power transferred across the thermal joint. Thus, the time

required for the TMP05/TMP06 to settle to the desired

accuracy is dependent on the package selected, the thermal

contact established in that particular application, and the

equivalent power of the heat source. In most applications, the

settling time is probably best determined empirically.

SELF-HEATING EFFECTS

The temperature measurement accuracy of the TMP05/TMP06

might be degraded in some applications due to self-heating.

Errors introduced are from the quiescent dissipation and power

dissipated when converting, that is, during TL. The magnitude of

these temperature errors is dependent on the thermal conduc-

tivity of the TMP05/TMP06 package, the mounting technique,

and the effects of airflow. Static dissipation in the TMP05/

TMP06 is typically 10 W operating at 3.3 V with no load. In the

5-lead SC-70 package mounted in free air, this accounts for a

temperature increase due to self-heating of

ΔT = PDISS × θJA = 10 µW × 211.4°C/W = 0.0021°C

(5)

In addition, power is dissipated by the digital output, which is

capable of sinking 800 µA continuously (TMP05). Under an

800 µA load, the output can dissipate

PDISS = (0.4 V)(0.8 mA)((TL)/TH + TL))

(6)

For example, with TL = 80 ms and TH = 40 ms, the power

dissipation due to the digital output is approximately 0.21 mW.

In a free-standing SC-70 package, this accounts for a tempera-

ture increase due to self-heating of

ΔT = PDISS × θJA = 0.21 mW × 211.4°C/W = 0.044°C (7)

This temperature increase adds directly to that from the

quiescent dissipation and affects the accuracy of the TMP05/

TMP06 relative to the true ambient temperature.

It is recommended that current dissipated through the device be

kept to a minimum, because it has a proportional effect on the

temperature error.

SUPPLY DECOUPLING

The TMP05/TMP06 should be decoupled with a 0.1 µF ceramic

capacitor between VDD and GND. This is particularly important,

if the TMP05/TMP06 are mounted remotely from the power

supply. Precision analog products such as the TMP05/TMP06

require a well-filtered power source. Because the TMP05/

TMP06 operate from a single supply, it might seem convenient

to simply tap into the digital logic power supply. Unfortunately,

the logic supply is often a switch-mode design, which generates

noise in the 20 kHz to 1 MHz range. In addition, fast logic gates

can generate glitches hundreds of mV in amplitude due to

wiring resistance and inductance.

If possible, the TMP05/TMP06 should be powered directly

from the system power supply. This arrangement, shown in

Figure 31, isolates the analog section from the logic switching

transients. Even if a separate power supply trace is not available,

however, generous supply bypassing reduces supply-line-

induced errors. Local supply bypassing consisting of a 0.1 µF

ceramic capacitor is critical for the temperature accuracy

specifications to be achieved. This decoupling capacitor must

be placed as close as possible to the TMP05/TMP06’s VDD pin.

A recommended decoupling capacitor is Phicomp’s 100 nF,

50 V X74.

Keep the capacitor package size as small as possible, because

ESL (equivalent series inductance) increases with increasing

package size. Reducing the capacitive value below 100 nF

increases the ESR (equivalent series resistance). Use of a

capacitor with an ESL of 1 nH and an ESR of 80 mΩ is

recommended.

0.1

µF

TMP05/

TMP06

TTL/CMOS

LOGIC

CIRCUITS

POWER

SUPPLY

Figure 31. Use Separate Traces to Reduce Power Supply Noise

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