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LTC2996

2996f

Typical applicaTion

FeaTures DescripTion

Temperature Sensor with

Alert Outputs

The LTC

2996 is a high accuracy temperature sensor

with adjustable overtemperature and undertemperature

thresholds and open drain alert outputs. It converts the

temperature of an external diode sensor or its own die

temperature to an analog output voltage while rejecting

errors due to noise and series resistance. The measured

temperature is compared against upper and lower limits

set with resistive dividers. If a threshold is exceeded, the

device communicates an alert by pulling low the corre-

spondent open drain logic output.

The LTC2996 gives ±1°C accurate temperature results

using commonly available NPN or PNP transistors or

temperature diodes built into modern digital devices. A

1.8V reference output simplifies threshold programming

and can be used as an ADC reference input.

The LTC2996 provides an accurate, low power solution

for temperature monitoring in a compact 3mm × 3mm

DFN package.

Remote Temperature Monitor with Overtemperature

and Undertemperature Thresholds

applicaTions

Converts Remote or Internal Diode Temperature to

Analog Voltage

Adjustable Overtemperature and Undertemperature

Thresholds

Voltage Output Proportional to Temperature

±1°C Remote Temperature Accuracy

±2°C Internal Temperature Accuracy

Built-In Series Resistance Cancellation

Open Drain Alert Outputs

2.25V to 5.5V Supply Voltage

1.8V Reference Voltage Output

200μA Quiescent Current

10-Lead 3mm × 3mm DFN Package

Temperature Monitoring and Measurement

System Thermal Control

Network Servers

Desktop and Notebook Computers

Environmental Monitoring

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

Diode Temperature

REMOTE DIODE TEMPERATURE (°C)

–50

0.8

PTAT

(V)

1.0

1.2

1.4

0 50

100

150

2996 TA01b

1.6

1.8

–25 25

125

REF

VTH

VTL

PTAT

–

LTC2996

1.8V

2.25V TO 5.5V

0.1µF

43k

36k

102k

2996 TA01a

GND

470pF MMBT3904

OT T > 70°C

UT T < –20°C

4mV/K

TEMPERATURE

CONTROL

SYSTEM

Summary of content (16 pages)

PAGE 1
LTC2996 Temperature Sensor with Alert Outputs Features n n n n n n n n n n n Description Converts Remote or Internal Diode Temperature to Analog Voltage Adjustable Overtemperature and Undertemperature Thresholds Voltage Output Proportional to Temperature ±1°C Remote Temperature Accuracy ±2°C Internal Temperature Accuracy Built-In Series Resistance Cancellation Open Drain Alert Outputs 2.25V to 5.5V Supply Voltage 1.
PAGE 2
LTC2996 Absolute Maximum Ratings Pin Configuration (Notes 1, 2) VCC ............................................................... –0.3V to 6V D+, D–, VPTAT, VREF.............................. –0.3V to VCC + 0.3V OT, UT, VTH, VTL.......................................... –0.3V to 6V Operating Ambient Temperature Range LTC2996C................................................. 0°C to 70°C LTC2996I..............................................–40°C to 85°C LTC2996H..........................................
PAGE 3
LTC2996 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 TCONV Temperature Update Interval KT VPTAT Slope Ideality Factor η = 1.004 VPTAT Load Regulation ILOAD = ±200μA TINT TRMT Internal Temperature Accuracy Remote Temperature Error, η = 1.
PAGE 4
LTC2996 Typical Performance Characteristics Remote Temperature Error vs Ambient Temperature Temperature Error with LTC2996 at Same Temperature as Remote Diode 3 TINTERNAL = TREMOTE Internal Temperature Error vs Ambient Temperature 3 TREMOTE = 35°C 2 2 1 1 1 0 –1 TINT ERROR (°C) 2 TRMT ERROR (°C) TRMT ERROR (°C) 3 TA = 25°C, VCC = 3.3V unless otherwise noted.
PAGE 5
LTC2996 Typical Performance Characteristics Load Regulation of VREF Voltage vs Current 1.22 VCC = 2.5V VCC = 3.5V VCC = 4.5V VCC = 5.5V 1.810 Single Wire Remote Temperature Error vs Ground Noise Load Regulation of VPTAT Voltage vs Current 10 VCC = 2.5V VCC = 3.5V VCC = 4.5V VCC = 5.5V 1.21 VPTAT (V) VREF (V) 1.20 1.800 1.19 1.18 1.790 1.17 1.780 –4 0 –2 2 LOAD CURRENT (mA) 4 1.16 –4 2 –2 0 LOAD CURRENT (mA) 2996 G10 UT, OT, vs Output Sink Current 0.1 0.01 0.
PAGE 6
LTC2996 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 LTC2996 measures the internal sensor temperature. Tie D+ to VCC if unused. OT: Overtemperature Logic Output.
PAGE 7
LTC2996 Block Diagram 6 VCC 8 VREF 1.8V 200k + 1.
PAGE 8
LTC2996 Operation Overview The LTC2996 provides a buffered voltage proportional to the absolute temperature of either an internal or a remote diode (VPTAT) and compares this voltage to thresholds that can be set by external resistor dividers from the on-board reference (VREF). 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 device in a microprocessor or FPGA.
PAGE 9
LTC2996 Applications Information Temperature Measurements Before each conversion, a voltage comparator connected to D+ automatically sets the LTC2996 into external or internal mode. Tying D+ to VCC enables internal mode, where VPTAT represents the die temperature. For VD+ more than 300mV below VCC (typical), the LTC2996 assumes that an external sensor is connected.
PAGE 10
LTC2996 Applications Information Note that bypass capacitors greater than 1nF will cause settling time errors of the different measurement currents and therefore introduce an error in the temperature measurement (see Typical Performance Characteristics). The LTC2996 compensates series resistance in the measurement path and thereby allows accurate remote temperature measurements even with several meters of distance between the sensor and the device.
PAGE 11
LTC2996 Applications Information Output Noise Filtering The VPTAT output typically exhibits 0.6mV RMS (0.25°C RMS) noise. For applications which require lower noise, digital or analog averaging can be applied to the output. Choose the averaging time according to: t AVG 2  [°C Hz ] 0.01  =   TNOISE where t AVG is the averaging time and TNOISE the desired temperature noise in °C RMS. For example, if the desired noise performance is 0.01°C RMS, set the averaging time to one second.
PAGE 12
LTC2996 Applications Information where ηACT denotes the actual ideality factor if an external sensor is used and T1 and T2 are the desired threshold temperatures in degrees Kelvin. In the Temperature Monitor example discussed earlier with thresholds at VTL = 0°C and VTH = 90°C and a desired reference current of 10μA, the required values for RTA, RTB and RTC can be calculated as : 2.
PAGE 13
LTC2996 Applications Information Remote Temperature Monitor with Overtemperature and Undertemperature Thresholds 2.25V TO 5.5V 0.1µF 1.8V VREF 43k VCC OT T > 70°C OT LTC2996 UT VTH 36k UT T < –20°C 4mV/K VPTAT VTL 102k TEMPERATURE CONTROL SYSTEM D+ 470pF MMBT3904 D– GND 2996 TA02 ASIC/FPGA/Processor Temperature Monitor 2.25V TO 5.5V 0.1µF 1.8V VREF 20.5k VCC OT OT T > 125°C LTC2996 UT T < 30°C UT VTH 38.
PAGE 14
LTC2996 Typical Applications Battery Stack Temperature Supervisor 2.25V TO 5.5V 0.1µF VCC VREF LTC2996 D+ TALERT 43.2k VTH UT VTL VPTAT BATTERY SUPERVISOR 10k OT INT 28k 110k GND D– LOW IF TEMPERATURE OF ANY CELL TCELL > 70°C OR TCELL < 0°C 0.1µF VCC VREF LTC2996 D+ OT 43.
PAGE 15
LTC2996 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev C) 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ±0.10 (4 SIDES) R = 0.125 TYP 6 0.40 ±0.10 10 1.65 ±0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.
PAGE 16
LTC2996 Typical Application Celsius Thermometer and 20°C to 25°C Thermostat 5V 220V AC 5LPCV24110 0.1µF VCC D+ MMBT3904 OT LTC2996 1.8V D– VPTAT GND 4mV/K VTL VTH VREF 118k 150k HEATER UT 470pF 0.1µF – 100k 1k + 62k 143k 1.8k 5V LTC1077 VOLTMETER 10mV/°C 0V AT 0°C 215mV CORRESPONDS TO 21.5°C 2996 TA06 1µF 63.