J

A

JA

DD S

DD

O

L

T = T +

(V I ) + (V

- V ) I

T

ª

º

¬

¼

(-5.50 mV /

V =

T + 1035 mV

(-5.50 mV /

V - 925 mV =

(T - 20

760 mV - 925 mV

50

u

¹

·

V - 925 mV =

(T - 20

LMT84, LMT84-Q1

www.ti.com

SNIS167C – MARCH 2013 – REVISED OCTOBER 2015

For example, if we want to resolve this equation, over a temperature range of 20°C to 50°C, we would proceed

as follows:

(4)

(5)

(6)

Using this method of linear approximation, the transfer function can be approximated for one or more

temperature ranges of interest.

8.4 Device Functional Modes

8.4.1 Mounting and Thermal Conductivity

The LMT84/LMT84-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 LMT84/LMT84-Q1 die is directly attached to the GND

pin. The temperatures of the lands and traces to the other leads of the LMT84/LMT84-Q1 will also affect the

temperature reading.

Alternatively, the LMT84/LMT84-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 LMT84/LMT84-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 a short circuit from

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 LMT84/LMT84-

Q1's die temperature is:

(7)

2

μA, the junction temperature would be 30.015°C, showing a self-heating error of only 0.015°C. Since the

LMT84/LMT84-Q1's junction temperature is the actual temperature being measured, care should be taken to

minimize the load current that the LMT84/LMT84-Q1 is required to drive. Thermal Information(1) shows the

thermal resistance of the LMT84/LMT84-Q1.

8.4.2 Output Noise Considerations

A push-pull output gives the LMT84/LMT84-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 LMT84/LMT84-

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 LMT84/LMT84-Q1.

8.4.3 Capacitive Loads

The LMT84/LMT84-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 LMT84/LMT84-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.

(1)

For information on self-heating and thermal response time see section Mounting and Thermal Conductivity.

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