LTC2997H 查看數據表（PDF） - Linear Technology

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LTC2997H

Remote/Internal Temperature Sensor

Linear Technology 

LTC2997

APPLICATIONS INFORMATION

Choosing a Sensor

The LTC2997 is factory calibrated for an ideality factor of

1.004, which is typical of the popular MMBT3904 NPN

transistor. Semiconductor purity and wafer-level processing

intrinsically limit device-to-device variation, making these

devices interchangeable between most manufacturers with

a temperature error of typically less than 0.5°C. Some

recommended sources are listed in Table 1:

Table 1. Recommended Transistors for Use as Temperature

Sensors.

MANUFACTURER

PART NUMBER

PACKAGE

Fairchild

Semiconductor

MMBT3904

SOT-23

Central Semiconductor

CMPT3904

SOT-23

Diodes, Inc.

MMBT3904

SOT-23

On Semiconductor

MMBT3904LT1

SOT-23

NXP

MMBT3904

SOT-23

Infineon

MMBT3904

SOT-23

Rohm

UMT3904

SC-70

Discrete two terminal diodes usually have ideality factors

significantly higher than 1.004 and are therefor not recom-

mended as remote sensing devices.

Protection

The LTC2997 can withstand up to ±4kV of electrostatic

discharge (ESD, human body). ESD beyond this voltage

can damage or degrade the device including lowering the

remote sensor measurement accuracy due to increased

leakage currents on D+ and D–.

To protect the sensing inputs against larger ESD strikes,

external protection can be added using TVS diodes to

ground (Figure 4). Care must be taken to choose diodes

with low capacitance and low leakage currents in order

not to degrade the external sensor measurement accuracy

(see Typical Performance Characteristics).

MMBT3904

PESD5Z6.0

10Ω

D+

LTC2997

220pF

10Ω

D–

GND

2997 F04

Figure 4. Increasing ESD Robustness with TVS Diodes

Ideality Factor Scaling

While an ideality factor value of 1.004 is typical of many

sensor devices, small deviations can yield significant tem-

perature errors. The ideality factor acts as a temperature

scaling factor. The temperature error for a 1% deviation

is 1% of the Kelvin temperature. Thus, at 25°C (298K) a

+1% accurate ideality factor error yields a +2.98 degree

error. At 85°C (358K) a +1% error yields a 3.58 degree

error. It is possible to scale the PTAT voltage if an external

sensor with an ideality factor other than 1.004 is used.

The scaling equation for the compensated PTAT voltage

is listed below. www.DataSheet.net/

LTC2997 Ideality Calibration Value:

ηCAL = 1.004

Actual Remote Sensor Ideality Value:

ηACT

Compensated PTAT Voltage:

VPTAT

_ COMP

=

ηCAL

η ACT

•

VPTAT _ MEAS

Compensated Kelvin Temperature:

TKELVIN _ COMP

=

ηCAL

η ACT

•

TKELVIN _ MEAS

Compensated Celsius Temperature:

TCELSIUS

_ COMP

=

ηCAL

η ACT

•(TKELVIN _ MEAS)

–

273.15

10

2997fa

Datasheet pdf - http://www.DataSheet4U.co.kr/

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