TMP03/TMP04

REV. 0

–10–

APPLICATIONS INFORMATION

Supply Bypassing

Precision analog products, such as the TMP03/TMP04, require

a well filtered power source. Since the TMP03/TMP04 operate

from a single +5 V supply, it seems 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 hundred of millivolts in amplitude due to

wiring resistance and inductance.

If possible, the TMP03/TMP04 should be powered directly

from the system power supply. This arrangement, shown in

Figure 27, will isolate the analog section from the logic switching

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

however, generous supply bypassing will reduce supply-line

induced errors. Local supply bypassing consisting of a 10

µF

tantalum electrolytic in parallel with a 0.1

µF ceramic capacitor

is recommended (Figure 28a).

10µF

TANT

0.1µF

TMP03/

TMP04

TTL/CMOS

LOGIC

CIRCUITS

+5V

POWER SUPPLY

Figure 27. Use Separate Traces to Reduce Power Supply

Noise

0.1µF

10µF

+5V

V+

GND

TMP03/

TMP04

0.1µF

10µF

+5V

V+

GND

TMP03/

TMP04

50

Ω

a.

b.

Figure 28. Recommended Supply Bypassing for the

TMP03/TMP04

The quiescent power supply current requirement of the

TMP03/TMP04 is typically only 900

µA. The supply current

will not change appreciably when driving a light load (such as a

CMOS gate), so a simple RC filter can be added to further

reduce power supply noise (Figure 28b).

TMP03/TMP04 Output Configurations

The TMP03 (Figure 29a) has an open-collector NPN output

which is suitable for driving a high current load, such as an

opto-isolator. Since the output source current is set by the pull-

up resistor, output capacitance should be minimized in TMP03

applications. Otherwise, unequal rise and fall times will skew the

pulse width and introduce measurement errors. The NPN

transistor has a breakdown voltage of 18 V.

TMP03

TMP04

V+

a.

b.

Figure 29. TMP03/TMP04 Digital Output Structure

The TMP04 has a “totem-pole” CMOS output (Figure 29b)

and provides rail-to-rail output drive for logic interfaces. The

rise and fall times of the TMP04 output are closely matched, so

that errors caused by capacitive loading are minimized. If load

capacitance is large, for example when driving a long cable, an

external buffer may improve accuracy. See the “Remote

Temperature Measurement” section of this data sheet for

suggestions.

Interfacing the TMP03 to Low Voltage Logic

The TMP03’s open-collector output is ideal for driving logic

gates that operate from low supply voltages, such as 3.3 V. As

shown in Figure 30, a pull-up resistor is connected from the low

voltage logic supply (2.9 V, 3 V, etc.) to the TMP03 output.

Current through the pull-up resistor should be limited to about

1 mA, which will maintain an output LOW logic level of

<200 mV.

+5V

V+

GND

TMP03

3.3k

Ω

TO LOW VOLTAGE

LOGIC GATE INPUT

+3.3V

Figure 30. Interfacing to Low Voltage Logic

Remote Temperature Measurement

When measuring a temperature in situations where high

common-mode voltages exist, an opto-isolator can be used to

isolate the output (Figure 31a). The TMP03 is recommended in

this application because its open-collector NPN transistor has a

higher current sink capability than the CMOS output of the

TMP04. To maintain the integrity of the measurement, the

opto-isolator must have relatively equal turn-on and turn-off

times. Some Darlington opto-isolators, such as the 4N32, have

a turn-off time that is much longer than their turn-on time. In

this case, the T1 time will be longer than T2, and an erroneous

reading will result. A PNP transistor can be used to provide

greater current drive to the opto-isolator (Figure 31b). An opto-

isolator with an integral logic gate output, such as the H11L1

from Quality Technology, can also be used (Figure 32).