SNIS177B March 2013 – September 2015 LMT90
PRODUCTION DATA.
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.
The LMT90 has a wide supply range and a 10 mV/°C output slope with a 500-mV DC offset at 25 °C. Therefore, it can easily be applied in many temperature-sensing applications where a single supply is required for positive and negative temperatures.
The LMT90 handles capacitive loading very well. Without any special precautions, the LMT90 can drive any capacitive load. The LMT90 has a nominal 2-kΩ output impedance (as can be seen in the Functional Block Diagram). The temperature coefficient of the output resistors is around 1300 ppm/°C. Taking into account this temperature coefficient and the initial tolerance of the resistors the output impedance of the LMT90 will not exceed 4 kΩ. In an extremely noisy environment it may be necessary to add some filtering to minimize noise pickup. TI recommends that 0.1 μF be added from VIN to GND to bypass the power supply voltage, as shown in Figure 13. In a noisy environment, it may be necessary to add a capacitor from the output to ground. A 1-μF output capacitor with the 4-kΩ output impedance will form a 40-Hz lowpass filter. Because the thermal time constant of the LMT90 is much slower than the 25-ms time constant formed by the RC, the overall response time of the LMT90 will not be significantly affected. For much larger capacitors this additional time lag will increase the overall response time of the LMT90.
For this design example, use the following design parameters in Table 1.
PARAMETER | VALUE | UNIT |
---|---|---|
Accuracy at 25°C | ±3.0 (maximum) | °C |
Accuracy Over –40°C to 125°C | ±4.0 (maximum) | °C |
Temperature slope | 10 | mV/°C |
Power Supply Voltage Range | 4.5 to 10 | V |
Output Impedance | 4 (maximum) | kΩ |
The LMT90 is a simple temperature sensor that provides an analog output. Therefore design requirements related to layout out weigh other requirements in importance, refer to Layout for a detailed description.