TMP06_15 datasheet(18/28 Pages) AD

18 / 28 page

TMP05/TMP06

Data Sheet

Rev. C | Page 18 of 28

LAYOUT CONSIDERATIONS

Digital boards can be electrically noisy environments and

glitches are common on many of the signals in the system.

The likelihood of glitches causing problems to the TMP05/

TMP06 OUT pin is very minute. The typical impedance of the

TMP05/TMP06 OUT pin when driving low is 55 Ω. When

driving high, the TMP05 OUT pin is similar. This low imped-

ance makes it very difficult for a glitch to break the VIL and VIH

thresholds. There is a slight risk that a sizeable glitch could

cause problems. A glitch can only cause problems when the

OUT pin is low during a temperature measurement. If a glitch

occurs that is large enough to fool the master into believing that

the temperature measurement is over, the temperature read

would not be the actual temperature. In most cases, the master

spots a temperature value that is erroneous and can request

another temperature measurement for confirmation. One area

that can cause problems is if this very large glitch occurs near

the end of the low period of the mark-space waveform, and the

temperature read back is so close to the expectant temperature

that the master does not question it.

One layout method that helps in reducing the possibility of a

glitch is to run ground tracks on either side of the OUT line.

Use a wide OUT track to minimize inductance and reduce noise

pickup. A 10 mil track minimum width and spacing is

recommended. Figure 31 shows how glitch protection traces

could be laid out.

GND

OUT

GND

10 MIL

Figure 31. Use Separate Traces to Reduce Power Supply Noise

Another method that helps reduce the possibility of a glitch is to

use a 50 ns glitch filter on the OUT line. The glitch filter

eliminates any possibility of a glitch getting through to the

master or being passed along a daisy chain.

TEMPERATURE MONITORING

The TMP05/TMP06 are ideal for monitoring the thermal

environment within electronic equipment. For example, the

surface-mounted package accurately reflects the exact thermal

conditions that affect nearby integrated circuits.

The TMP05/TMP06 measure and convert the temperature at

the surface of their own semiconductor chip. When the

TMP05/TMP06 are used to measure the temperature of a

nearby heat source, the thermal impedance between the heat

source and the TMP05/TMP06 must be considered. Often, a

thermocouple or other temperature sensor is used to measure

the temperature of the source, while the TMP05/TMP06

temperature is monitored by measuring TH and TL. Once the

thermal impedance is determined, the temperature of the heat

source can be inferred from the TMP05/TMP06 output.

One example of using the TMP05/TMP06’s unique properties is

in monitoring a high power dissipation microprocessor. Each

TMP05/TMP06 part, in a surface-mounted package, is

mounted directly beneath the microprocessor’s pin grid array

(PGA) package. In a typical application, the TMP05/TMP06

output is connected to an ASIC, where the pulse width is

measured. The TMP05/TMP06 pulse output provides a

significant advantage in this application because it produces a

linear temperature output while needing only one I/O pin and

without requiring an ADC.

DAISY-CHAIN APPLICATION

This section provides an example of how to connect two

TMP05s in daisy-chain mode to a standard 8052 microcon-

troller core. The ADuC812 is the microcontroller used and the

core processing engine is the 8052. Figure 31 shows how to

interface to the 8052 core device. The TMP05 Program Code

Example 1 section shows how to communicate from the

ADuC812 to two daisy-chained TMP05s. This code can also be

used with the ADuC831 or any microprocessor running on an

8052 core.

TIMER T0

STARTS

TEMPSEGMENT = 1

TEMPSEGMENT = 2 TEMPSEGMENT = 3

TEMP_HIGH2

TEMP_HIGH1

TEMP_LOW0

TEMP_LOW1

TEMP_HIGH0

INTO

Figure 32. Reference Diagram for Software Variables

in the TMP05 Program Code Example 1

Figure 32 is a diagram of the input waveform into the ADuC812

from the TMP05 daisy chain. It illustrates how the code’s variables

are assigned and it should be referenced when reading the

TMP05 Program Code Example 1. Application notes showing

the TMP05 working with other types of microcontrollers are

available from Analog Devices at www.analog.com.

Figure 33 shows how the three devices are hardwired together.

Figure 34 to Figure 36 are flow charts for this program.

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