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TMP03FT9Z 데이터시트(PDF) 10 Page - Analog Devices |
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TMP03FT9Z 데이터시트(HTML) 10 Page - Analog Devices |
10 / 16 page 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+ DOUT GND 5V TMP03/ TMP04 10 F 0.1 F V+ DOUT 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+ DOUT DOUT 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 DOUT 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). |
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