ADJ

N.C.

N.C.

-

N.C.

VIA to ground plane

VIA to power plane

+

N.C.

N.C.

R1

LM135, LM135A, LM235, LM235A, LM335, LM335A

SNIS160E – MAY 1999 – REVISED FEBRUARY 2015

www.ti.com

9 Power Supply Recommendations

Ensure the LM335 is biased properly with a current ranging 0.4 mA to 5 mA.

10 Layout

10.1 Layout Guidelines

The LM135 is applied easily in the same way as other integrated-circuit temperature sensors. Glue or cement the

device to a surface and the temperature should be within about 0.01°C of the surface temperature.

Efficient temperature transfer assumes that the ambient air temperature is almost the same as the surface

temperature where the LM135 leads are attached. If there is a great difference between the air temperature and

the surface temperature, the actual temperature of the LM135 die would be at an intermediate temperature

between the two temperatures. For example, the TO-92 plastic package, where the copper leads are the

principal thermal path to carry heat into the device, can be greatly affected by airflow. The temperature sensed

by the TO92 package could greatly depend on velocity of the airflow as well.

To lessen the affect of airflow, ensure that the wiring to the LM135 (leads and wires connected to the leads) is

held at the same temperature as the surface temperature that is targeted for measurement. To insure that the

temperature of the LM135 die is not affected by the air temperature, mechanically connect the LM135 leads with

a bead of epoxy to the surface being measured. If air temperature is targeted for measurement ensure that the

PCB surface temperature is close to the air temperature. Keep the LM135 away from offending PCB heat

sources such as power regulators. One method commonly used for thermal isolation is to route a thermal well as

shown in Figure 33 with the smallest possible geometry traces connecting back to rest of the PCB.

10.2 Layout Example

Figure 33. Layout Example

16

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Product Folder Links: LM135 LM135A LM235 LM235A LM335 LM335A