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 V
IL
and V
IH
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
10 MIL
10 MIL
10 MIL
10 MIL
03340-043
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 T
H
and T
L
. 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_HIGH2TEMP_HIGH1
TEMP_LOW0 TEMP_LOW1
TEMP_HIGH0
INTO
INTO INTO
03340-035
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.
