TMP03/TMP04

REV. A

–10–

APPLICATIONS INFORMATION

Supply Bypassing

Precision analog products, such as the TMP03, require a well-

filtered power source. Since the TMP03 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 induc-

tance.

If possible, the TMP03 should be powered directly from the

system power supply. This arrangement, shown in Figure 3, will

isolate the analog section from the logic switching transients. Even

if a separate power supply trace is not available, however, gener-

ous supply bypassing will reduce supply-line induced errors.

Local supply bypassing consisting of a 10

µF tantalum electro-

lytic in parallel with a 0.1

µF ceramic capacitor is recommended

(Figure 4a).

TTL/CMOS

LOGIC

CIRCUITS

TMP03/

TMP04

10 F

TANT

0.1 F

5V

POWER SUPPLY

+

Figure 3. Use Separate Traces to Reduce Power Supply

Noise

TMP03/

TMP04

10 F

0.1 F

V+

GND

5V

TMP03/

TMP04

10 F

0.1 F

V+

GND

5V

50

a.

b.

Figure 4. Recommended Supply Bypassing for the

TMP03

The quiescent power supply current requirement of the TMP03

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 4b).

TMP03 Output Configurations

The TMP03 (Figure 5a) 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

pulsewidth and introduce measurement errors. The NPN tran-

sistor has a breakdown voltage of 18 V.

V+

TMP03

TMP04

a.

b.

Figure 5. TMP03 Digital Output Structure

The TMP04 has a “totem-pole” CMOS output (Figure 5b) 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 ca-

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

external buffer may improve accuracy. See the “Remote Tem-

perature 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 6, 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.

TMP03

5V

GND

3.3V

3.3k

V+

TO LOW VOLTAGE

LOGIC GATE INPUT

Figure 6. Interfacing to Low Voltage Logic

Remote Temperature Measurement

When measuring a temperature in situations where high com-

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

the output (Figure 7a). 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 7b). An opto-

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

from Quality Technology, can also be used (Figure 8).