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ZHCSCH2E January 2014 – October 2017 LMT87

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- MPDS025J
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9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

9.1 Application Information

The LMT87 features make it suitable for many general temperature-sensing applications. It can operate down to 2.7-V supply with 5.4-µA power consumption. Package options like the through-hole TO-92 package also allow the LMT87 to be mounted onboard, off-board, to a heat sink, or on multiple unique locations in the same application.

9.2 Typical Applications

9.2.1 Connection to ADC

LMT87 suggested_conn_sampling_analog_to_digital_nis170.gif

Figure 13. Suggested Connection to a Sampling Analog-to-Digital Converter Input Stage

9.2.1.1 Design Requirements

Most CMOS ADCs found in microcontrollers and ASICs have a sampled data comparator input structure. When the ADC charges the sampling cap, it requires instantaneous charge from the output of the analog source such as the LMT87 temperature sensor and many op amps. This requirement is easily accommodated by the addition of a capacitor (C_FILTER).

9.2.1.2 Detailed Design Procedure

The size of C_FILTER depends on the size of the sampling capacitor and the sampling frequency. Because not all ADCs have identical input stages, the charge requirements will vary. This general ADC application is shown as an example only.

9.2.1.3 Application Curve

Figure 14. Analog Output Transfer Function

9.2.2 Conserving Power Dissipation With Shutdown

LMT87 conversing_power_dissipation_with_shutdown_nis170.gif

Figure 15. Simple Shutdown Connection of the LMT87

9.2.2.1 Design Requirements

Because the power consumption of the LMT87 is less than 9 µA, it can simply be powered directly from any logic gate output and therefore not require a specific shutdown pin. The device can even be powered directly from a microcontroller GPIO. In this way, it can easily be turned off for cases such as battery-powered systems where power savings are critical.

9.2.2.2 Detailed Design Procedure

Simply connect the V_DD pin of the LMT87 directly to the logic shutdown signal from a microcontroller.

9.2.2.3 Application Curves

INDENT:

Time: 500 μs/div; Top trace: V_DD 1 V/div;
Bottom trace: OUT 1 V/div

Figure 16. Output Turnon Response Time Without a Capacitive Load and V_DD = 3.3 V

INDENT:

Time: 500 μs/div; Top trace: V_DD 2 V/div;
Bottom trace: OUT 1 V/div

Figure 18. Output Turnon Response Time Without a Capacitive Load and V_DD = 5 V

INDENT:

Time: 500 μs/div; Top trace: V_DD 1 V/div;
Bottom trace: OUT 1 V/div

Figure 17. Output Turnon Response Time With a 1.1-nF Capacitive Load and V_DD = 3.3 V

INDENT:

Time: 500 μs/div; Top trace: V_DD 2 V/div;
Bottom trace: OUT 1 V/div

Figure 19. Output Turnon Response Time With a 1.1-nF Capacitive Load and V_DD = 5 V