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 LMT85 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 13. Analog Output Transfer Function

9.2.2.1 Design Requirements

Because the power consumption of the LMT85-Q1 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 micro controller 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 LMT85-Q1 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 15. Output Turnon Response Time Without a Capacitive Load and V_DD = 3.3 V

INDENT:

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

Figure 17. Output Turnon Response Time With 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 16. Output Turnon Response Time Without a Capacitive Load and V_DD = 5 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 With 1.1-nF Capacitive Load and V_DD = 5 V