OUT

LMT87

GND

OPTIONAL

BYPASS

CAPACITANCE

J

A

JA

DD S

DD

OUT

L

T = T +

(V I ) + (V

- V

) I

T

ª

º

¬

¼

LMT87, LMT87-Q1

www.ti.com

SNIS170C – JAN 2014 – REVISED OCTOBER 2015

8.4 Device Functional Modes

8.4.1 Mounting and Thermal Conductivity

The LMT87 and LMT87-Q1 can be applied easily in the same way as other integrated-circuit temperature

sensors. It can be glued or cemented to a surface.

To ensure good thermal conductivity, the backside of the LMT87 and LMT87-Q1 die is directly attached to the

GND pin (Pin 2 of the SC70 DCK package). The temperatures of the lands and traces to the other leads of the

LMT87 and LMT87-Q1 will also affect the temperature reading.

Alternatively, the LMT87 and LMT87-Q1 can be mounted inside a sealed-end metal tube, and can then be

dipped into a bath or screwed into a threaded hole in a tank. As with any IC, the LMT87 and LMT87-Q1 and

accompanying wiring and circuits must be kept insulated and dry, to avoid leakage and corrosion. This is

especially true if the circuit may operate at cold temperatures where condensation can occur. If moisture creates

Printed-circuit coatings are often used to ensure that moisture cannot corrode the leads or circuit traces.

junction temperature due to its power dissipation. The equation used to calculate the rise in the LMT87 and

LMT87-Q1's die temperature is:

(7)

= 2

μA, the junction temperature would be 30.014°C, showing a self-heating error of only 0.014°C. Since the

junction temperature of the LMT87 and LMT87-Q1 is the actual temperature being measured, care should be

taken to minimize the load current that the LMT87 and LMT87-Q1 is required to drive. Thermal Information

shows the thermal resistance of the LMT87 and LMT87-Q1.

8.4.2 Output Noise Considerations

A push-pull output gives the LMT87 and LMT87-Q1 the ability to sink and source significant current. This is

beneficial when, for example, driving dynamic loads like an input stage on an analog-to-digital converter (ADC).

In these applications the source current is required to quickly charge the input capacitor of the ADC. The LMT87

and LMT87-Q1 is ideal for this and other applications which require strong source or sink current.

measured during bench tests. Its typical attenuation is shown in Figure 8 found in the Typical Characteristics

section. A load capacitor on the output can help to filter noise.

For operation in very noisy environments, some bypass capacitance should be present on the supply within

approximately 5 centimeters of the LMT87 and LMT87-Q1.

8.4.3 Capacitive Loads

The LMT87 and LMT87-Q1 handles capacitive loading well. In an extremely noisy environment, or when driving

a switched sampling input on an ADC, it may be necessary to add some filtering to minimize noise coupling.

Without any precautions, the LMT87 and LMT87-Q1 can drive a capacitive load less than or equal to 1100 pF, as

shown in Figure 10. For capacitive loads greater than 1100 pF, a series resistor may be required on the output,

as shown in Figure 11.

Figure 10. LMT87 No Decoupling Required for Capacitive Loads Less than 1100 pF

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Product Folder Links: LMT87 LMT87-Q1