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LTC2997

2997fa

TYPICAL APPLICATION

FEATURES DESCRIPTION

Remote/Internal

Temperature Sensor

The LTC

2997 is a high-accuracy analog output temperature

sensor. It converts the temperature of an external sensor or

its own temperature to an analog voltage output. A built-in

algorithm eliminates errors due to series resistance be-

tween the LTC2997 and the sensor diode.

The LTC2997 gives accurate results with low-cost diode-

connected NPN or PNP transistors or with integrated

temperature transistors on microprocessors or FPGAs.

Tying pin D

to V

configures the LTC2997 to measure

its internal temperature.

The LTC2997 provides an additional 1.8V reference voltage

output which can be used as an ADC reference input or

for generating temperature threshold voltages to compare

against the V

PTAT

output.

The LTC2997 provides a precise and versatile micropower

solution for accurate temperature sensing.

Single Remote Temperature Sensor

APPLICATIONS

Converts Remote Sensor or Internal Diode

Temperature to Analog Voltage

±1°C Remote Temperature Accuracy

±1.5°C Internal Temperature Accuracy

Built-In Series Resistance Cancellation

2.5V to 5.5V Supply Voltage

1.8V Reference Voltage Output

3.5ms V

PTAT

Update Time

4mV/°K Output Gain

170A Quiescent Current

Available in 6-Pin 2mm × 3mm DFN Package

Temperature Measurement

Remote Temperature Measurement

Environmental Monitoring

System Thermal Control

Desktop and Notebook Computers

Network Servers

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

PTAT

vs Remote Sensor Temperature

REF

4mV/K

1.8V

2.5V TO 5.5V

0.1µF

–

LTC2997

MMBT 3904

470pF

2997 TA01a

PTAT

GND

REMOTE SENSOR TEMPERATURE (°C)

–50

0.8

PTAT

(V)

1.0

1.2

1.4

050

100

150

2997 TA01b

1.6

1.8

–25 25

125

Summary of content (18 pages)

PAGE 1
LTC2997 Remote/Internal Temperature Sensor FEATURES DESCRIPTION n The LTC®2997 is a high-accuracy analog output temperature sensor. It converts the temperature of an external sensor or its own temperature to an analog voltage output. A built-in algorithm eliminates errors due to series resistance between the LTC2997 and the sensor diode. n n n n n n n n n Converts Remote Sensor or Internal Diode Temperature to Analog Voltage ±1°C Remote Temperature Accuracy ±1.
PAGE 2
LTC2997 ABSOLUTE MAXIMUM RATINGS (Notes 1, 2) Terminal Voltages VCC........................................................... –0.3V to 6V D+, D –, VPTAT, VREF ......................–0.3V to VCC + 0.3V Operating Ambient Temperature Range LTC2997C ................................................ 0°C to 70°C LTC2997I .............................................–40°C to 85°C LTC2997H .......................................... –40°C to 125°C Storage Temperature Range ..................
PAGE 3
LTC2997 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, unless otherwise noted. SYMBOL PARAMETER VCC Supply Voltage UVLO Supply Undervoltage Lockout Threshold ICC Average Supply Current CONDITIONS VCC Falling MIN TYP l MAX UNITS 2.5 3.3 5.5 V l 1.7 1.9 2.1 V l 120 170 250 μA 1.797 1.793 1.790 1.787 1.8 1.8 1.8 1.8 1.803 1.804 1.807 1.808 V V V V ±1.
PAGE 4
LTC2997 TYPICAL PERFORMANCE CHARACTERISTICS Remote Temperature Error vs TA with Remote Diode at 25°C 3 2 2 2 1 1 1 0 –1 TINT ERROR (°C) 3 0 –1 –2 –2 –3 –50 –25 0 25 50 75 TA (°C) –3 –50 –25 100 125 150 –1 0 25 50 75 TA (°C) –3 –50 –25 100 125 150 0 25 50 75 TA (°C) 100 125 150 2997 G02 Temperature Error vs VCC - Remote/Internal, T VCC 2997 G03 Remote Temperature Error vs CDECOUPLE (Between D+ and D –) Remote Temperature Error vs Series Resistance, TRS 0.4 1.5 0.2 1.0 0.
PAGE 5
LTC2997 TYPICAL PERFORMANCE CHARACTERISTICS Load Regulation of VPTAT – Voltage vs Current 1.28 VCC = 2.5V VCC = 3.5V VCC = 4.5V VCC = 5.5V 1.810 Supply Current vs Temperature 200 VCC = 2.5V VCC = 3.5V VCC = 4.5V VCC = 5.5V 1.27 190 SUPPLY CURRENT (μA) Load Regulation of VREF – Voltage vs Current 1.820 TA = 25°C, VCC = 3.3V unless otherwise noted. VPTAT (V) VREF (V) 1.26 1.800 1.25 1.24 1.790 0 –2 2 LOAD CURRENT (mA) –4 4 1.
PAGE 6
LTC2997 PIN FUNCTIONS D+: Diode Sense Current Source. D+ sources the remote diode sensing current. Connect D+ to the anode of the remote sensor device. It is recommended to connect a 470pF bypass capacitor between D+ and D–. Larger capacitors may cause settling time errors (see Typical Performance Characteristics). If D+ is tied to VCC, the LTC2997 measures the internal sensor temperature. Tie D+ to VCC if unused. VPTAT : VPTAT Voltage Output.
PAGE 7
LTC2997 BLOCK DIAGRAM VSUPPLY 4 VCC + – UVLO TEMPERATURE TO VOLTAGE CONVERTER + – 1 2 3 1.2V EXT/INT MUX + D+ 1.
PAGE 8
LTC2997 OPERATION The Block Diagram shows the main components of the LTC2997. The LTC2997 measures temperature using either a remote or internal diode and provides a buffered voltage proportional to absolute temperature (VPTAT) and a buffered 1.8V reference voltage. Remote temperature measurements usually use a diode connected transistor as a temperature sensor, allowing the remote sensor to be a discrete NPN (ex. MMBT3904) or an embedded PNP device in a microprocessor or FPGA.
PAGE 9
LTC2997 APPLICATIONS INFORMATION Power Up and UVLO The basic LTC2997 application using an external NPN transistor is shown in Figure 2. 2.5V TO 5.5V Input Noise Filtering 0.1μF D+ MMBT3904 VCC VREF 1.8V LTC2997 470pF D– GND VPTAT 4mV/K 2997 F02 Figure 2. Basic Application Circuit The VCC pin must exceed the undervoltage threshold of 1.9V (typical) for normal operation. For VCC below UVLO the LTC2997 enters power-on reset and VPTAT is pulled low.
PAGE 10
LTC2997 APPLICATIONS INFORMATION Choosing a Sensor 10Ω 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.
PAGE 11
LTC2997 TYPICAL APPLICATIONS 2.5V TO 5.5V 0.1μF MMBT3904 VCC D+ VREF 1.8V LTC2997 470pF D– GND VPTAT 4mV/K 2997 F05 Figure 5. Single Remote Temperature Sensor 2.5V TO 5.5V 0.1μF D+ VCC VREF μC 1.8V LTC2997 D– GND VPTAT 4mV/K A/D 2997 F06 Figure 6. Internal Temperature Sensor 2.5V TO 5.5V 0.1μF D+ CPU/ FPGA/ ASIC VCC VREF 1.8V LTC2997 470pF D– GND VPTAT 4mV/K 2997 F07 Figure 7.
PAGE 12
LTC2997 TYPICAL APPLICATIONS 2.5V TO 5.5V 0.1μF D+ 2N3904 VCC 1.8V VREF LTC2997 470pF D– GND 4mV/K VPTAT 2997 F08 Figure 8. Single Wire Remote Temperature Sensor 0.30 2.5V TO 5.5V D+ VCC >1k VPTAT LTC2997 VPTAT(FILTER) CFILTER D– GND 2997 F09 VPTAT NOISE (°C RMS) 0.25 0.1μF 0.20 0.15 0.10 0.05 0 0.005 5 0.5 0.05 RC TIME CONSTANT (ms) 50 Figure 9. Output Noise Filter 2.5V TO 5.5V CAT6 STP CABLE 10m MAXIMUM 0.1μF D+ MMBT 3904 VCC VREF 1.
PAGE 13
LTC2997 TYPICAL APPLICATIONS MEASURE TEMPERATURE AND SET TARGET TEMPERATURE WITH RESISTIVE DIVIDER INTEGRATE TEMPERATURE ERROR PWM OSCILLATOR 5V 100μF 10M 0.1μF 100pF 10M 200k ZXM64PO35 D + VCC 1k – VPTAT 100k LTC2997 470pF 5V LTC6079 – + D– GND VREF + LTC6079 CET 3904 22k VTARGET 75k VREF 100k 1M 10Ω RHEATER 2997 F11 Figure 11. Analog PWM Heater Controller CET 3904 5V 10Ω RHEATER 0.1μF D+ VCC VPTAT – 4mV/K LTC2997 470pF D– GND VREF + 1.
PAGE 14
LTC2997 TYPICAL APPLICATIONS 2.5V TO 5.5V 0.1μF VCC D+ VREF LTC2997 470pF MMBT3904 1.8V D– GND VPTAT 4mV/K 2997 F13 Figure 13. Remote Diode Sensor Insensitive to Cable Connection Polarity 12V 5V 0.1μF 39k B6015L12F 68k FAN MMBT 3904 D+ VCC 10k VREF – LTC2997 470pF VPTAT D– GND VCC + IRF3708 OUT MOD LTC6078 LTC6692 DIV SET 390k GND 2997 F14 Figure 14.
PAGE 15
LTC2997 TYPICAL APPLICATIONS 0.1μF 150k 2.5V TO 5.5V 1.8k 0.1μF 5V D+ VCC VREF 1.8V LTC2997 D– VPTAT 4mV/K 100k 1k – 62k GND 143k 7 LTC1150 1 + 4 10mV/°C 0V AT 0°C 1μF –5V 2997 F15 Figure 15. Celsius Thermometer 0.1μF 255k 2.5V TO 5.5V 0.1μF D+ VREF 1.8V LTC2997 D– 5V 270k VCC VPTAT 4mV/K 100k – 7 LTC1150 1 + 4 62k 10mV/°F 0V AT 0°F 1μF GND 2997 F16 –5V Figure 16.
PAGE 16
LTC2997 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DCB Package 6-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1715 Rev A) 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 (2 SIDES) 2.15 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 1.35 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 2.00 ±0.10 (2 SIDES) R = 0.05 TYP 3.00 ±0.10 (2 SIDES) 0.40 ± 0.10 4 6 1.65 ± 0.10 (2 SIDES) PIN 1 NOTCH R0.20 OR 0.
PAGE 17
LTC2997 REVISION HISTORY REV DATE DESCRIPTION A 9/11 Changed 4mV/°C to 4mV/°K in Features 1 Updated Description 1 Updated Electrical Characteristics 3 Added Graph G15 5 Updated Pin Functions PAGE NUMBER 6 Updated Applications Information 9, 10 Updated Figures 9, 10, 13, 15, 16 12, 14, 15 Updated Related Parts 18 2997fa 17
PAGE 18
LTC2997 TYPICAL APPLICATION 5V + OUT = 4mV/K LTC6078 TYPE K THERMOCOUPLE – 1.3k 5V 127k 10k 5.6pF 0.1μF D+ VCC VPTAT LTC2997 D– GND VREF 2997 F17 Figure 17. Thermocouple Thermometer with Cold Junction Compensation RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC2990 Remote/Internal Temperature, Voltage and Current Monitor Measures Two Remote Diode Temperatures, ±1°C Accuracy, 0.