VP

VN

19

LMT01-SP

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SNIS205 – JANUARY 2019

Product Folder Links: LMT01-SP

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Copyright © 2019, Texas Instruments Incorporated

9 Power Supply Recommendations

Because the LMT01-SP is only a 2-pin device the power pins are common with the signal pins, thus the LMT01-

SP has a floating supply that can vary greatly. The LMT01-SP has an internal regulator that provides a stable

voltage to internal circuitry.

Take care to prevent reverse biasing of the LMT01-SP as exceeding the absolute maximum ratings may cause

damage to the device.

Power supply ramp rate can effect the accuracy of the first result transmitted by the LMT01-SP. As shown in

Figure 32 with a 1-ms rise time, the LMT01-SP output code is at 1286, which converts to 30.125°C. The scope

photo shown in Figure 33 reflects what happens when the rise time is too slow. In Figure 33, the power supply

(yellow trace) is still ramping up to final value while the LMT01-SP (red trace) has already started a conversion.

This causes the output pulse count to decrease from the previously shown 1286, to 1282 (or 29.875°C). Thus,

for slow ramp rates, TI recommends that the first conversion be discarded. For even slower ramp rates, more

than one conversion may have to be discarded as TI recommends that either the power supply be within final

value before a conversion is used or that ramp rates be faster than 2.5 ms.

Yellow trace = 1 V/div, Red trace = 100 mV/div, Time Base = 20

ms/div

LMT01-SP Pulse Count = 1286

VP – VN = 3.3 V

Rise Time = 1 ms

Figure 32. Output Pulse Count With Appropriate Power

Supply Rise Time

Yellow trace = 1 V/div, Red trace = 100 mV/div, Time base = 20

ms/div

LMT01-SP Pulse Count = 1282

VP – VN = 3.3 V

Rise Time = 100 ms

Figure 33. Output Pulse Count With Slow Power Supply

Rise Time

10 Layout

10.1 Layout Guidelines

The LMT01-SP can be mounted as a through-hole component for ambient sensing or cemented to a surface

using a thermally conductive paste. The traces leading to the pads of the LMT01-SP should be kept as small as

possible to minimize their effect on the temperature the LMT01-SP is measuring. The metal lid of the device has

no internal connections to the die and is thus floating. If desired, a wire can be soldered from the lid to ground.

10.2 Layout Example

Figure 34. Layout Example (CTO-92/HTA Package)