7.1 Overview

The LMT88 device is a precision analog output CMOS integrated-circuit temperature sensor that operates over a temperature range of −55°C to 130°C . The power supply operating range is 2.4 V to 5.5 V. The transfer function of LMT88 is predominately linear, yet has a slight predictable parabolic curvature. The accuracy of the LMT88 when specified to a parabolic transfer function is typically ±1.5°C at an ambient temperature of 30°C. The temperature error increases linearly and reaches a maximum of ±5°C at the temperature range extremes. The temperature range is affected by the power supply voltage. At a power supply voltage of 2.7 V to 5.5 V, the temperature range extremes are 130°C and −55°C. Decreasing the power supply voltage to 2.4 V changes the negative extreme to −30°C, while the positive remains at 130°C.

The LMT88 quiescent current is less than 10 μA. Therefore, self-heating is less than 0.02°C in still air. Shutdown capability for the LMT88 is intrinsic because its inherent low power consumption allows it to be powered directly from the output of many logic gates or does not necessitate shutdown at all.

The temperature sensing element is comprised of a simple base emitter junction that is forward biased by a current source. The temperature sensing element is then buffered by an amplifier and provided to the OUT pin. The amplifier has a simple class A output stage thus providing a low impedance output that can source 16 µA and sink 1 µA.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 LMT88 Transfer Function

The LMT88 transfer function can be described in different ways with varying levels of precision. A simple linear transfer function, with good accuracy near 25°C, is:

Equation 1. V_O = −11.69 mV/°C × T + 1.8663 V

Over the full operating temperature range of −55°C to 130°C, best accuracy can be obtained by using the parabolic transfer function.

Equation 2. V_O = (−3.88×10⁻⁶×T²) + (−1.15×10⁻²×T) + 1.8639

solving for T:

Equation 3.

Using Equation 2 the following temperature to voltage output characteristic table can be generated.

Table 1. Temperature to Voltage Output Characteristic Table

TEMP (°C)	VOUT (V)		TEMP (°C)	VOUT (V)		TEMP (°C)	VOUT (V)		TEMP (°C)	VOUT (V)		TEMP (°C)	VOUT (V)		TEMP (°C)	VOUT (V)		TEMP (°C)	VOUT (V)
-55	2.4847		-28	2.1829		-1	1.8754		26	1.5623		53	1.2435		80	0.9191		107	0.5890
-54	2.4736		-27	2.1716		0	1.8639		27	1.5506		54	1.2316		81	0.9069		108	0.5766
-53	2.4625		-26	2.1603		1	1.8524		28	1.5389		55	1.2197		82	0.8948		109	0.5643
-52	2.4514		-25	2.1490		2	1.8409		29	1.5271		56	1.2077		83	0.8827		110	0.5520
-51	2.4403		-24	2.1377		3	1.8294		30	1.5154		57	1.1958		84	0.8705		111	0.5396
-50	2.4292		-23	2.1263		4	1.8178		31	1.5037		58	1.1838		85	0.8584		112	0.5272
-49	2.4181		-22	2.1150		5	1.8063		32	1.4919		59	1.1719		86	0.8462		113	0.5149
-48	2.4070		-21	2.1037		6	1.7948		33	1.4802		60	1.1599		87	0.8340		114	0.5025
-47	2.3958		-20	2.0923		7	1.7832		34	1.4684		61	1.1480		88	0.8219		115	0.4901
-46	2.3847		-19	2.0810		8	1.7717		35	1.4566		62	1.1360		89	0.8097		116	0.4777
-45	2.3735		-18	2.0696		9	1.7601		36	1.4449		63	1.1240		90	0.7975		117	0.4653
-44	2.3624		-17	2.0583		10	1.7485		37	1.4331		64	1.1120		91	0.7853		118	0.4529
-43	2.3512		-16	2.0469		11	1.7369		38	1.4213		65	1.1000		92	0.7731		119	0.4405
-42	2.3401		-15	2.0355		12	1.7253		39	1.4095		66	1.0880		93	0.7608		120	0.4280
-41	2.3289		-14	2.0241		13	1.7137		40	1.3977		67	1.0760		94	0.7486		121	0.4156
-40	2.3177		-13	2.0127		14	1.7021		41	1.3859		68	1.0640		95	0.7364		122	0.4032
-39	2.3065		-12	2.0013		15	1.6905		42	1.3741		69	1.0519		96	0.7241		123	0.3907
-38	2.2953		-11	1.9899		16	1.6789		43	1.3622		70	1.0399		97	0.7119		124	0.3782
-37	2.2841		-10	1.9785		17	1.6673		44	1.3504		71	1.0278		98	0.6996		125	0.3658
-36	2.2729		-9	1.9671		18	1.6556		45	1.3385		72	1.0158		99	0.6874		126	0.3533
-35	2.2616		-8	1.9557		19	1.6440		46	1.3267		73	1.0037		100	0.6751		127	0.3408
-34	2.2504		-7	1.9442		20	1.6323		47	1.3148		74	0.9917		101	0.6628		128	0.3283
-33	2.2392		-6	1.9328		21	1.6207		48	1.3030		75	0.9796		102	0.6505		129	0.3158
-32	2.2279		-5	1.9213		22	1.6090		49	1.2911		76	0.9675		103	0.6382		130	0.3033
-31	2.2167		-4	1.9098		23	1.5973		50	1.2792		77	0.9554		104	0.6259		—	—
-30	2.2054		-3	1.8984		24	1.5857		51	1.2673		78	0.9433		105	0.6136		—	—
-29	2.1941		-2	1.8869		25	1.5740		52	1.2554		79	0.9312		106	0.6013		—	—

Solving Equation 2 for T:

Equation 4.

For other methods of calculating T see Detailed Design Procedure.

7.4 Device Functional Modes

The LMT88's only functional mode is that it has an analog output inversely proportional to temperature.