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LTC2995

2995f

TYPICAL APPLICATION

FEATURES DESCRIPTION

Temperature Sensor and

Dual Voltage Monitor with

Alert Outputs

The LTC

2995 is a high accuracy temperature sensor

and dual supply monitor. It converts the temperature of

an external diode sensor and/or its own die temperature

to an analog output voltage while rejecting errors due to

noise and series resistance. Two supply voltages and the

measured temperature are compared against upper and

lower limits set with resistive dividers. If a threshold is

exceeded, the device communicates an alert by pulling

low the correspondent open drain logic output.

The LTC2995 gives ±1°C accurate temperature results

using commonly available NPN or PNP transistors or

temperature diodes built into modern digital devices. Volt-

ages are monitored with 1.5% accuracy. A 1.8V reference

output simplifies threshold programming and can be used

as an ADC reference input.

The LTC2995 provides an accurate, low power solution for

temperature and voltage monitoring in a compact 3mm ×

3mm QFN package.

Dual OV/UV Supply and Single OT/UT Remote Temperature Monitor

APPLICATIONS

Monitors Temperature and Two Voltages

Voltage Output Proportional to Temperature

Adjustable Thresholds for Temperature and Voltage

±1°C Remote Temperature Accuracy

±2°C Internal Temperature Accuracy

±1.5% Voltage Threshold Accuracy

3.5ms Update Time

2.25V to 5.5V Supply Voltage

Input Glitch Rejection

Adjustable Reset Timeout

220A Quiescent Current

Open Drain Alert Outputs

Available in 3mm × 3mm QFN Package

Network Servers

Core, I/O Voltage Monitors

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

050

100

150

2995 TA01b

1.6

1.8

–25 25

125

VH1

VL1

VH2

VL2

PTAT

TO2

TO1

–

LTC2995

2.5V

1.2V

0.1µF

64.4k

10.2k

45.3k

2995 TA01a

VT1VT2 GND TMRV

REF

20k 20k 140k

470pF

TEMPERATURE

SENSOR

ASIC

SYSTEM

MONITOR

OT T > 125°C

4mV/K

UT T < 75°C

+10%

–10%

45.3k

10.2k

194k

5nF

Summary of content (20 pages)

PAGE 1
LTC2995 Temperature Sensor and Dual Voltage Monitor with Alert Outputs DESCRIPTION FEATURES n n n n n n n n n n n n n Monitors Temperature and Two Voltages Voltage Output Proportional to Temperature Adjustable Thresholds for Temperature and Voltage ±1°C Remote Temperature Accuracy ±2°C Internal Temperature Accuracy ±1.5% Voltage Threshold Accuracy 3.5ms Update Time 2.25V to 5.
PAGE 2
LTC2995 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Notes 1, 2) VCC .............................................................. –0.3V to 6V TMR, D+, D–, DS, PS, VPTAT, VREF........ –0.3V to VCC + 0.3V UV, OV, TO1, T02 .......................................... –0.3V to 6V VH1, VL1, VH2, VL2, VT1, VT2 ..................... –0.3V to 6V Operating Ambient Temperature Range LTC2995C ................................................ 0°C to 70°C LTC2995I .............................................
PAGE 3
LTC2995 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 CONDITIONS MIN l Temperature Error vs Supply TRS Series Resistance Cancellation Error 5 UNITS ms mV/K ±1.5 mV ±0.
PAGE 4
LTC2995 TIMING DIAGRAMS VLn Monitor Timing VHn Monitor Timing VHn VUOT VLn tUOD UV VUOT tUOTO tUOD OV 1V tUOTO 1V 2995 TD01 VHn Monitor Timing (TMR Pin Strapped to VCC) VHn VUOT VLn Monitor Timing (TMR Pin Strapped to VCC) VLn tUOD UV 2995 TD02 VUOT tUOD tUOD OV 1V 2995 TD03 tUOD 1V 2995 TD04 2995f 4
PAGE 5
LTC2995 TYPICAL PERFORMANCE CHARACTERISTICS Remote Temperature Error vs Ambient Temperature Temperature Error with LTC2995 at Same Temperature as Remote Diode 3 TINTERNAL = TREMOTE TRMT ERROR (°C) TRMT ERROR (°C) 2 1 0 –1 –2 Internal Temperature Error vs Ambient Temperature 3 TREMOTE = 25°C 2 2 1 1 TINT ERROR (°C) 3 TA = 25°C, VCC = 3.3V unless otherwise noted. 0 –1 –2 –3 –50 –25 0 25 50 75 TA (°C) 0 25 50 75 TA (°C) 0.4 4 4 0.2 2 2 ERROR (°C) 6 ERROR (°C) 6 0 –2 –2 –0.
PAGE 6
LTC2995 TYPICAL PERFORMANCE CHARACTERISTICS Load Regulation of VREF – Voltage vs Current 1.80 10 VCC = 2.25V VCC = 3.5V VCC = 4.5V VCC = 5.5V 1.20 VPTAT (V) VREF (V) 1.22 VCC = 2.25V VCC = 3.5V VCC = 4.5V VCC = 5.5V 1.81 Single Wire Remote Temperature Error vs Ground Noise Load Regulation of VPTAT – Voltage vs Current ABSOLUTE TEMPERATURE ERROR (°C) 1.82 TA = 25°C, VCC = 3.3V unless otherwise noted. 1.18 1.16 1.79 1.78 1.14 –4 –2 2 0 LOAD CURRENT (mA) 4 –4 2 –2 0 LOAD CURRENT (mA) 0.
PAGE 7
LTC2995 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 LTC2995 measures the internal sensor temperature. Tie D+ to VCC if unused. D –: Diode Sense Current Sink. Connect D – to the cathode of the remote sensor device.
PAGE 8
LTC2995 PIN FUNCTIONS resistor between VPTAT and the load to ensure stability. VPTAT is pulled low when the supply voltage goes below the under voltage lockout threshold. VT1: Temperature Threshold 1. When VPTAT crosses the voltage on VT1 with a polarity set by the PS pin, TO1 is pulled low. Tie VT1 to GND if unused. VREF: Voltage Reference Output. VREF provides a 1.8V reference voltage. VREF can drive up to ±200μA of load current and up to 1000pF of capacitive load.
PAGE 9
LTC2995 OPERATION Overview The LTC2995 combines the functionality of a temperature measurement and monitor device with a dual voltage supervisor. It 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). The LTC2995 also provides four voltage threshold inputs that are continuously compared to an internal 0.
PAGE 10
LTC2995 APPLICATIONS INFORMATION Temperature Measurements Choosing an External Sensor The LTC2995 continuously measures the sensor diode at different test currents and generates a voltage proportional to the absolute temperature of the sensor at the VPTAT pin. The voltage at VPTAT is updated every 3.5ms. The LTC2995 is factory calibrated for an ideality factor of 1.004, which is typical of the popular MMBT3904 NPN transistor.
PAGE 11
LTC2995 APPLICATIONS INFORMATION Leakage currents at D+ affect the precision of the remote temperature measurements. 100nA leakage current leads to an additional error of 2°C (see Typical Performance Characteristics). components. Noise around odd multiples of 6kHz (±20%)is amplified by the measurement algorithm and converted at a DC offset in the temperature measurement (see Typical Performance Characteristics).
PAGE 12
LTC2995 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 0.015°C RMS, set the averaging time to one second.
PAGE 13
LTC2995 APPLICATIONS INFORMATION Temperature Thresholds The threshold voltages at VT1 and VT2 can be set with the 1.8V reference voltage (VREF) and a resistive divider as shown in Figure 5. VREF = 1.8V RTC η VPTAT SLOPE = ACT t mV K The following design procedure can be used to size the resistive divider. 1. Calculate Threshold Voltages: VT1 = T1 • 4 mV ηACT • K 1.004 VT2 = T2 • 4 1.8V VT2 mV ηACT • K 1.
PAGE 14
LTC2995 APPLICATIONS INFORMATION 4. Finally RTC is determined by: R TC = 1.8V – VT2 IREF In the Temperature Monitor example discussed earlier with thresholds at VT1 = 60°C and VT2 = 90°C and a desired reference current of 10μA, the required values for RTA, RTB and RTC can be calculated as: 1.332V R TA = = 133.2k 10μA Vn RC LTC2995 VHn – + + – RB UVn 0.5V – VLn + OVn RA 2995 F07 R TB = R TC = 1.452V – 1.332V = 12k 10μA 1.8V – 1.452V = 34.
PAGE 15
LTC2995 APPLICATIONS INFORMATION 2. Find RB to set the UV trip point of the monitor: RB = 0.5V 5V • – 453 ≅ 10k 10μA 4.5V 3. Determine RC to complete the design: RC = 5V – 453Ω – 100Ω ≈ 442k 10μA The two extreme conditions, with a relative accuracy of 1.5% and resistance accuracy of 1%, result in: ⎛ RC t 0.99 ⎞ VUV(MIN) = 0.5V t 0.985 t ⎜1+ ⎟ ⎝ (RA + RB) t 1.01⎠ and ⎛ RC t 1.01 ⎞ VUV(MAX) = 0.5V t 1.015 t ⎜1+ ⎟ ⎝ (RA + RB) t 0.
PAGE 16
LTC2995 APPLICATIONS INFORMATION Timing of Alert Outputs Digital Output Characteristics The LTC2995 has an adjustable timeout period (tUOTO) that holds UV, OV, TO1 or TO2 asserted after any faults have cleared. This delay will minimize the effect of input noise with a frequency above 1/tUOTO. The DC characteristics of the UV, OV, TO1 and TO2 pull-up and pull-down strength are shown in the Typical Performance Characteristics section.
PAGE 17
LTC2995 TYPICAL APPLICATIONS ±10% Voltage Monitor (1.8V and 2.5V) and Internal/Remote Overtemperature Monitor 2.5V POWER SUPPLIES 1.8V VCC 0.1μF D+ PS 470pF DS 124k MMBT390 D– VH1 LTC2995 10.2k VPTAT VL1 45.3k TO2 194k TO1 VH2 OV 10.2k UV VL2 VT2 VREF 45.
PAGE 18
LTC2995 TYPICAL APPLICATIONS Celsius Thermometer and ±10% Voltage Monitor (1.8V and 2.5V) 2.5V POWER SUPPLIES 1.8V 0.1μF D+ VCC 0.1μF 470pF PS 100k + LTC1150 LTC2995 10.2k 4mV/K VL1 VPTAT VH2 OV +10% UV –10% 62k 1k 194k 10.2k VL2 VT2 VT1 GND TO2 TMR 10mV/°C 0V AT 0°C – 143k 45.3k 1.8k 5V 1.8V VREF VH1 45.
PAGE 19
LTC2995 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UD Package 20-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1720 Rev A) 0.70 ±0.05 3.50 ± 0.05 (4 SIDES) 1.65 ± 0.05 2.10 ± 0.05 PACKAGE OUTLINE 0.20 ±0.05 0.40 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 3.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD R = 0.115 TYP 0.75 ± 0.05 R = 0.
PAGE 20
LTC2995 TYPICAL APPLICATION Dual OV/UV ±10% Supply and 75°C/125°C OT/OT Remote Temperature Monitor ASIC/ CPU/ FPGA 2.5V 1.2V D+ 470pF VCC 0.1μF D– PS DS 64.4k VH1 LTC2995 10.2k VL1 45.3k TO2 194k TO1 VH2 10.2k VL2 TMR 45.