LTC2995
1
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
n Monitors Temperature and Two Voltages
n Voltage Output Proportional to Temperature
n Adjustable Thresholds for Temperature and Voltage
n ±1°C Remote Temperature Accuracy
n ±2°C Internal Temperature Accuracy
n ±1.5% Voltage Threshold Accuracy
n 3.5ms Update Time
n 2.25V to 5.5V Supply Voltage
n Input Glitch Rejection
n Adjustable Reset Timeout
n 220A Quiescent Current
n Open Drain Alert Outputs
n Available in 3mm × 3mm QFN Package
n Network Servers
n Core, I/O Voltage Monitors
n Desktop and Notebook Computers
n 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.
VPTAT vs Remote
Diode Temperature
REMOTE DIODE TEMPERATURE (°C)
–50
0.8
VPTAT (V)
1.0
1.2
1.4
050
100 150
2995 TA01b
1.6
1.8
–25 25 75 125
VCC
PS
DS
VH1
VL1
VH2
VL2
VPTAT
TO2
TO1
OV
UV
D+
D
LTC2995
2.5V
1.2V
0.1µF
64.4k
10.2k
45.3k
2995 TA01a
VT1VT2 GND TMRVREF
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
LTC2995
2
2995f
PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
20 19 18 17 16
7 8
TOP VIEW
21
UD PACKAGE
20-LEAD (3mm × 3mm) PLASTIC QFN
910
VL1
VH2
VL2
VT2
VT1
UV
OV
TO2
T01
VREF
VH1
PS
DS
GND
TMR
D+
D
VPTAT
VCC
GND
12
11
13
14
15
4
5
3
2
1
6
TJMAX = 150°C, θJA = 59°C/W
EXPOSED PAD PCB GROUND CONNECTED OPTIONAL
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VCC Supply Voltage l2.25 5.5 V
UVLO Supply Undervoltage Lockout Threshold VCC Falling l1.7 1.9 2.1 V
ICC Average Supply Current l220 300 µA
Temperature Measurement
VREF Reference Voltage LTC2995
LTC2995C
LTC2995I
LTC2995H
l
l
l
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
VREF Load Regulation ILOAD = ±200A l±1.5 mV
Remote Diode Sense Current –8 –192 µA
ORDER INFORMATION
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 .............................................40°C to 85°C
LTC 2995H ......................................... 40°C to 125°C
Storage Temperature Range ..................65°C to 150°C
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC2995CUD#PBF LTC2995CUD#TRPBF LFQV 20-Lead (3mm × 3mm) Plastic QFN 0°C to 70°C
LTC2995IUD#PBF LTC2995IUD#TRPBF LFQV 20-Lead (3mm × 3mm) Plastic QFN –40°C to 85°C
LTC2995HUD#PBF LTC2995HUD#TRPBF LFQV 20-Lead (3mm × 3mm) Plastic QFN –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
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.
LTC2995
3
2995f
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.
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: All currents into pins are positive; all voltages are referenced to
GND unless otherwise noted.
Note 3: Remote diode temperature, not LTC2995 temperature.
Note 4: Guaranteed by design and test correlation.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Tconv Temperature Update Interval l3.5 5 ms
KTVPTAT Slope Ideality Factor η = 1.004 4mV/K
VPTAT Load Regulation ILOAD = ±200A ±1.5 mV
Tint Internal Temperature Accuracy
TAMB = –40°C to 125°C
±0.5
±2
±1 °C
°C
TRMT Remote Temperature Error, η = 1.004 0°C to 85°C (Notes 3, 4)
–40°C to 0°C (Notes 3, 4)
85°C to 125°C (Notes 3, 4)
±0.25
±0.25
±0.25
±1
±1.5
±1.5
°C
°C
°C
Temperature Noise 0.15
0.01
°CRMS
°CRMS/√Hz
TVCC Temperature Error vs Supply l±0.5 °C/V
TRS Series Resistance Cancellation Error RSERIES = 100 l±0.25 ±1 °C
Temperature and Voltage Monitoring
VUOT Undervoltage/Overvoltage Threshold l492 500 508 mV
TOFF VT1, VT2 Offset l–3 –1 1 °C
∆THYST VT1, VT2 Temperature Hysteresis l2 5 10 °C
tUOD UV, OV Input 5mV Above/Below Threshold l0.5 2 ms
IIN VH1, VL1, VH2, VL2, VT1, VT2, Input Current l±20 nA
tUOTO UV/OV Time-Out-Period CTMR = TMR Open
CTMR = 1nF l5
0.5
10 20
ms
ms
ITMR TMR Current l±2.5 µA
Three State Pins DS, PS
VDS,PS(H,TH) PS, DS Input High Threshold lVCC – 0.4 VCC – 0.1 V
VDS,PS(H,TL) PS, DS Input Low Threshold l0.1 0.4 V
IDS,PS(IN,HL) PS, DS High, Low Input Current DS, PS at 0V or VCC l±4 µA
IDS,PS(IN,Z) Allowable Leakage Current l±1 µA
Digital Outputs
VOH High Level Output Voltage,
TO1, TO2, UV, OV
I = –0.5A lVCC – 1.2 V
VOL Low Level Output Voltage,
TO1, TO2, UV, OV
I = 3mA l0.4 V
LTC2995
4
2995f
TIMING DIAGRAMS
VLn
OV
VUOT
1V
tUOD tUOTO
2995 TD02
VHn
UV
VUOT
1V
tUOD tUOD
2995 TD03
VLn
OV
VUOT
1V
tUOD tUOD
2995 TD04
VHn Monitor Timing
VHn Monitor Timing (TMR Pin Strapped to VCC)
VLn Monitor Timing
VLn Monitor Timing (TMR Pin Strapped to VCC)
VHn
UV
VUOT
1V
tUOD tUOTO
2995 TD01
LTC2995
5
2995f
TYPICAL PERFORMANCE CHARACTERISTICS
Remote Temperature Error
vs Series Resistance
Remote Temperature Error
vs CDECOUPLE (Between D+ and D)
Temperature Error with LTC2995 at
Same Temperature as Remote Diode
Remote Temperature Error
vs Ambient Temperature
Internal Temperature Error
vs Ambient Temperature
UVLO vs Temperature
VCC Rising, Falling
Buffered Reference Voltage
vs Temperature
Temperature Error vs Supply
Voltage
VPTAT Noise vs Averaging Time
TA = 25°C, VCC = 3.3V unless otherwise noted.
TA (°C)
–50
–3
TINT ERROR (°C)
–2
0
–1
75 150100
2995 G03
3
1
2
–25 0 25 50 125
TA (°C)
–50
–3
TRMT ERROR (°C)
–2
0
–1
75 150100
2995 G01
3
1
2
–25 0 25 50 125
TINTERNAL = TREMOTE
TA (°C)
–50
–3
TRMT ERROR (°C)
–2
0
–1
75 150100
2995 G02
3
1
2
–25 0 25 50 125
TREMOTE = 25°C
SERIES RESISTANCE ()
0
–6
ERROR (°C)
–4
0
–2
800600
2995 G05
2
6
4
200 400 12001000
DECOUPLE CAPACITOR (nF)
0
ERROR (°C)
0
–2
–4
–6 86
2995 G06
4
2
6
24 10
TA (°C)
–50
UVLO (V)
1.8
2.0
1.6 25 75 150
2995 G08
2.2
0–25 50 100 125
VCC RISING
VCC FALLING
TA (°C)
1.790
VREF (V)
1.795
2995 G09
1.800
1.810
1.805
–50 25 75 150
0–25 50 100 125
VCC (V)
ERROR (°C)
–0.2
0
–0.4
–0.6 35
2995 G04
0.2
0.6
0.4
246
AVERAGING TIME (ms)
0.01
0
VPTAT NOISE (°C RMS)
0.05
0.15
0.20
0.10
11000100
2995 G07
0.1 10
LTC2995
6
2995f
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Temperature
Load Regulation of VPTAT
Voltage vs Current
Single Wire Remote Temperature
Error vs Ground Noise
Load Regulation of VREF
Voltage vs Current
TA = 25°C, VCC = 3.3V unless otherwise noted.
Delay vs Comparator Overdrive
UV, OV, TO1, TO2 vs Output Sink
Current
Reset Timeout Period
vs Capacitance
OVERDRIVE (mV)
0
DELAY (µs)
200
110
2995 G13
800
600
400
1200
1000
100
FREQUENCY (kHz)
0.1
0.01
ABSOLUTE TEMPERATURE ERROR (°C)
0.1
110 1000
2995 G12
1
10
100
VAC = 50mVP-P
TMR PIN CAPACITANCE (nF)
RESET TIMEOUT tUOTO (ms)
0.1 1 10 100
2995 G15
100
10
1
10000
1000
1000
I (mA)
VUV/OV/TO1/TO2 (V)
0 5 10 15 20 25 30
2995 G14
0.6
0.4
0.2
0
1
0.8
35
LOAD CURRENT (mA)
1.78
VREF (V)
1.80
1.79
0
2995 G10
1.82
1.81
–4 –2 2 4
VCC = 2.25V
VCC = 3.5V
VCC = 4.5V
VCC = 5.5V
LOAD CURRENT (mA)
–4
1.14
VPTAT (V)
1.18
1.16
–2 0 4
2995 G11
1.20
1.22
2
VCC = 2.25V
VCC = 3.5V
VCC = 4.5V
VCC = 5.5V
SUPPLY CURRENT (µA)
240
230
220
2995 G16
250
TA (°C)
–50
200
210
50 100
–25 0 25 75 125 150
LTC2995
7
2995f
PIN FUNCTIONS
D+: Diode Sense Current Source. D+ sources the remote
diode sensing current. Connect D+ to the anode of the re-
mote 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+ i s t i e d t o V CC, 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. Tie D to GND for single
wire remote temperature measurement (see Applications
Information) or internal temperature sensing.
DS: Diode Select Input. Three state pin that selects tem-
perature sensor location. Tie DS to VCC to monitor the
temperature of the internal diode or to GND to monitor the
temperature of the external diode. When DS is left uncon-
nected, the LTC2995 monitors both sensors alternately.
If D+ is tied to VCC, the LTC2995 measures the internal
sensor temperature regardless of the state of DS.
Exposed Pad: Exposed pad may be left open or soldered
to GND for better thermal coupling.
GND: Device Ground
OV: Overvoltage Logic Output. Open drain logic output
that pulls to GND when either the voltage at VL1 or VL2
is above 0.5V. Held low for a programmable delay time
set by the capacitor connected to pin TMR. OV has a weak
400k pull-up to VCC and may be pulled above VCC using
an external pull-up. Leave OV open if unused.
PS: Polarity Select Input. Selects the polarity of tempera-
ture thresholds VT1 and VT2. Connect PS to VCC to config-
ure VT1 as undertemperature and VT2 as overtemperature
threshold. Leave PS unconnected to configure both VT1
and VT2 as overtemperature thresholds. Connect PS to
GND to configure both VT1 and VT2 as undertemperature
thresholds. Tie to VCC if temperature thresholds are unused.
TMR: Reset Delay Timer. Attach an external capacitor
(CTMR) to GND to set the delay time until alerts on TO1,
TO2, UV and OV are reset. Leaving the pin open generates
a minimum delay of 500s. Capacitance on this pin adds
an additional 8ms/nF reset delay time. Tie TMR to VCC to
bypass the timer.
TO1: Temperature Logic Output 1. Open drain logic output
that pulls to GND when VPTAT crosses the threshold voltage
on pin VT1 with a polarity set by the PS pin (see Table 3
in Applications Information). When VPTAT crosses the
threshold voltage on pin VT1 with opposite polarity, an
additional hysteresis of 20mV is required to release TO1
high after a delay adjustable by the capacitor on TMR. TO1
has a weak 400k pull-up to VCC and may be pulled above
VCC using an external pull-up. Leave TO1 open if unused.
TO2: Temperature Logic Output 2. Open drain logic output
that pulls to GND when VPTAT crosses the threshold voltage
on pin VT2 with a polarity set by the PS pin (see Table 3
in Applications Information). When VPTAT crosses the
threshold voltage on pin VT2 with opposite polarity, an
additional hysteresis of 20mV is required to release TO2
high after a delay adjustable by the capacitor on TMR. TO2
has a weak 400k pull-up to VCC and may be pulled above
VCC using an external pull-up. Leave TO2 open if unused.
UV: Undervoltage Logic Output. Open drain logic output
that pulls to GND when either the voltage at VH1 or VH2
is below 0.5V. Held low for an adjustable delay time set
by the capacitor connected to pin TMR. UV has a weak
400k pull-up to VCC and may be pulled above VCC using
an external pull-up. Leave pin open if unused.
VCC: Supply Voltage. Bypass this pin to GND with a 0.1F
(or greater) capacitor. VCC operating range is 2.25V to 5.5V.
VH1, VH2: Voltage High Inputs 1 and 2. When the voltage
on either pin is below 0.5V, an undervoltage condition is
triggered. Tie pin to VCC if unused.
VL1, VL2: Voltage Low Inputs 1 and 2. When the voltage
on either pin is above 0.5V, an overvoltage condition is
triggered. Tie pin to GND if unused.
VPTAT: Proportional to Absolute Temperature Voltage
Output. The voltage on this pin is proportional to the
selected sensors absolute temperature. An internal or
external sensor is chosen with the DS pin. V
PTAT can
drive up to ±200A of load current and up to 1000pF of
capacitive load. For larger load capacitances insert a 1k
LTC2995
8
2995f
resistor between VPTAT and the load to ensure stability.
VPTAT is pulled low when the supply voltage goes below
the under voltage lockout threshold.
VREF: Voltage Reference Output. VREF provides a 1.8V
reference voltage. VREF can drive up to ±200A of load
current and up to 1000pF of capacitive load. For larger
load capacitances insert 1k between VREF and the load
to ensure stability. Leave VREF open if unused.
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.
VT2: Temperature Threshold 2. When VPTAT crosses the
voltage on VT2 with a polarity set by the PS pin, TO2 is
pulled low. Tie VT2 to VCC if unused.
PIN FUNCTIONS
BLOCK DIAGRAM
2995 BD
VH1 CH1
CH2
CL2
CT2
CT1
CL1
UVLO
2V
VCC
VL1
VH2
VL2
VT2
VREF
VT1
VPTAT
20
1
2
3
+
+
+
+
+
+
+
+
1.3M
500k
0.5V
200k
200k
1.2V
1.8V
400k
UVLO
11
4
5
8
18 7DD+
DS PS GND
619
T TO V
CONVERTER
TO1/TO2
PULSE
GENERATOR
UV PULSE
GENERATOR
OSCILLATOR
UV
VCC
400k
TMR
OV
VCC
400k
TO2
VCC
400k
TO1
VCC
400k
OV PULSE
GENERATOR
3 STATE
DECODE
17
3 STATE
DECODE
12
13
14
15
16
VCC
9
1
LTC2995
9
2995f
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 0.5V
reference allowing two systems voltages to be monitored
for undervoltage and overvoltage conditions.
Diode Temperature Sensor
Temperature measurements are conducted by measuring
the voltage of either an internal or an external diode with
multiple test currents. The relationship between diode
voltage VD and diode current ID can be solved for absolute
Temperature in degrees Kelvin T:
T=q
ηtktVD
ln ID
IS
where IS is a process dependent factor on the order of
10–13A, η is the diode ideality factor, k is the Boltzmann
constant and q is the electron charge. This equation shows
a relationship between temperature and voltage dependent
on the process depended variable IS. Measuring the same
diode (with the same value IS) at two different currents
(ID1 and ID2) yields an expression independent of IS:
ln ID2
ID1
T=q
ηtktVD2 –V
D1
Series Resistance Cancellation
Resistance in series with the remote diode causes a positive
temperature error by increasing the measured voltage at
each test current. The composite voltage equals:
VD+VERROR kT
qtln ID
IS+RStID
The LTC2995 removes this error term from the sensor
signal by subtracting a cancellation voltage VCANCEL. A
resistance extraction circuit uses one additional current
measurement to determine the series resistance in the
measurement path. Once the correct value of the resistor is
determined, VCANCEL equals VERROR. Now the temperature
to voltage converter input signal is free from errors due
to series resistance.
LTC2995 can cancel series resistances up several hundred
ohms (see Typical Performance Characteristics curves).
Higher series resistances cause the cancelation voltage
to saturate.
LTC2995
10
2995f
Temperature Measurements
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 gain of VPTAT is calibrated to 4mV/K for the measure-
ment of the internal diode as well as for remote diodes
with an ideality factor of 1.004.
TKELVIN =VPTAT
4mV /K (η=1.004)
If an external sensor with an ideality factor different from
1.004 is used, the gain of VPTAT will be scaled by the ratio
of the actual ideality factor (ηACT) to 1.004. In these cases,
the temperature of the external sensor can be calculated
from VPAT by:
TKELVIN =VPTAT
4mV / K 1.004
ηACT
Temperature in degrees Celsius can be deduced from
degrees Kelvin by:
T
CELSIUS = TKELVIN – 273.15
The three-state diode select pin (DS) determines whether
the temperature of the external or the internal diode is
measured and displayed at VPTAT as described in Table 1.
Table 1. Diode Selection
DIODE LOCATION DS PIN
Internal VCC
External GND
Both Open
If the DS pin is left open, the LTC2995 measures both
diodes alternately and VPTAT changes every 30ms from the
voltage corresponding to the temperature of the internal
sensor to the voltage corresponding to the temperature
of the external sensor. If D+ is tied to VCC, the LTC2995
measures the internal diode regardless of the state of
the DS pin.
APPLICATIONS INFORMATION
Choosing an External Sensor
The LTC2995 is factory calibrated for an ideality factor of
1.004, which is typical of the popular MMBT3904 NPN
transistor. Semiconductor purity and wafer level process-
ing intrinsically limit device-to-device variation, making
these devices interchangeable between manufacturers
with a temperature error of typically less than 0.5°C. Some
recommended sources are listed in Table 2:
Table 2 Recommended Transistors for Use As Temperature
Sensors
MANUFACTURER PART NUMBER PACKAGE
Fairchild
Semiconductor
MMBT3904 SOT-23
Central
Semiconductor
CMBT3904 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 are not recommended as
remote sensing devices as their ideality factor is typically
much higher than 1.004. Also MOS transistors are not
suitable as they don’t exhibit the required current to tem-
perature relationship. Furthermore gold doped transistors
(low beta), high frequency and high voltage transistors
should be avoided as remote sensing devices.
Connecting an External Sensor
The change in sensor voltage per °C is hundreds of
microvolts, so electrical noise must be kept to a mini-
mum. Bypass D+ and D with a 470pF capacitor close to
the LTC2995 to suppress external noise. Recommended
shielding and PCB trace considerations for best noise
immunity are illustrated in Figure 1.
Figure 1. Recommended PCB Layout
D+
D
LTC2995
2995 F01
GND
470pF
GND SHIELD TRACE
NPN SENSOR
LTC2995
11
2995f
D+
D
470pF
LTC2995
2N3904
2995 F02
GND
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).
Note that bypass capacitors greater than 1nF will cause
settling time errors in the different measurement cur-
rents and therefore introduce an error in the temperature
measurement (see Typical Performance Characteristics).
The LTC2995 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. The cable
length between the sensor and the LTC2995 is only limited
by the mutual capacitance introduced between D+ and
D which degrades measurement accuracy (see Typical
Performance Characteristics).
For example an AT6 cable with 50pF/m should be kept
shorter than ~20m to keep the capacitance less than 1nF.
To save wiring, the cathode of the remote sensor can
also be connected to remote GND and D to local GND
as shown below.
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).
The LTC2995 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+ or D.
To protect the sensing inputs against larger ESD strikes,
external protection can be added using TVS diodes to
ground (Figure 3). 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 curves).
The temperature measurement of the LTC2995 relies only
on differences between the diode voltage at multiple test
circuits. Therefore DC offsets smaller than 300mV between
remote and local GND do not impact the precision of the
temperature measurement. The cathode of the sensor
can accommodate modest ground shifts across a system
which is beneficial in applications where a good thermal
connectivity of the sensor to a device whose temperature
is to be monitored (shunt resistor, coil, etc.) is required.
Care must be taken if the potential difference between
the cathode and D does not only content DC but also AC
Figure 2. Single Wire Remote Temperature Sensing
Figure 3. Increasing ESD Robustness with TVS Diodes
To make the connection of the cable to the IC polarity
insensitive during installation, two sensor transistors
with opposite polarity at the end of a two wire cable can
be used as shown on Figure 4.
Again, care must be taken that the leakage current of the
second transistor does not degrade the measurement
accuracy.
Figure 4. Polarity Insensitive Remote Diode Sensor
D+
D
220pF
10 LTC2995
MMBT3904
PESD5Z6.0 2995 F03
GND
10
D+
D
LTC2995
MMBT3904 470pF
2995 F04
GND
LTC2995
12
2995f
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:
2
tAVG =0.01[]
°CHz
TNOISE
where tAVG 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. See Typical Performance Characteristics.
Temperature Monitoring
The LTC2995 continuously compares the voltage at VPTAT
to the voltages at the pins VT1 and VT2 to detect either an
overtemperature (OT) or undertemperature (UT) condition.
The VT1 comparator output drives the open-drain logic
output pin TO1 and the VT2 comparator output drives the
open-drain logic output pin TO2. The polarity of these
comparisons is configured via the three-state polarity
select pin (PS) (Table 3).
Table 3. Temperature Polarity Selection
PS PIN FUNCTION CONDITION OUTPUT
VCC
VT1 Undertemperature
Threshold VPTAT < VT1 TO1 Pulled Low
VT2 Overtemperature
Threshold VPTAT > VT2 TO2 Pulled Low
Open
VT1 Overtemperature
Threshold VPTAT > VT1 TO1 Pulled Low
VT2 Overtemperature
Threshold VPTAT > VT2 TO2 Pulled Low
GND
VT1 Undertemperature
Threshold VPTAT < VT1 TO1 Pulled Low
VT2 Undertemperature
Threshold VPTAT < VT2 TO2 Pulled Low
If pin PS is connected to VCC, the voltage on VT1 becomes
an undertemperature threshold and the voltage on VT2
an overtemperature threshold. In this configuration TO1 is
pulled low if the voltage VPTAT falls during five consecutive
conversions below the undertemperature threshold VT1.
Once pulled low, TO1 is released high again if VPTAT rises
above VT1 plus an additional hysteresis of about 20mV.
Accordingly, T02 is pulled low if the voltage VPTAT rises
above the overtemperature threshold VT2 and –once pulled
lowTO2 is released high if VPTAT falls below VT2 minus
an additional hysteresis of about 20mV. Leaving PS uncon-
nected configures both VT1 and VT2 as overtemperature
thresholds and connecting PS to GND configures them
both as undertemperature thresholds. If the internal and
external sensors are monitored alternately by leaving DS
unconnected, VT1 becomes a dedicated threshold for the
internal sensor and VT2 becomes a dedicated threshold
for the external sensor.
Temperature Monitor Design Example
The LTC2995 can be configured to give an early warning
if the temperature of the internal sensor rises above 60°C
and an alarm if the temperature passes 90°C. Tie the DS
pin to VCC to select the internal sensor and leave the pin
PS unconnected to configure both input voltages VT1 and
VT2 as overtemperature thresholds. The voltages at VT1
and VT2 are set to:
VT1 =(60K +273.15K) 4mV
K=1.332V
VT2 =(90K +273.15K) 4mV
K=1.452V
When VPTAT reaches the threshold voltage on pin VT1, TO1
is pulled low indicating an overtemperature early warning.
If the temperature reaches 90°C TO2 is also pulled low,
indicating an overtemperature alarm.
Once the temperature drops below each threshold, the
corresponding TO pins will return high after a time-out-
period (tUOTO) set by the capacitor connected to TMR.
LTC2995
13
2995f
D+DS
D
1.2V
200k
400k
1.8V
VCC
VREF
RTC
VT2
VT1
VCC
VPTAT
PS
TO2
TO1
3.3V
LTC2995
2995 F06
OT ALARM
OT WARNING
RTB
RTA
GND
+
+
+
TO1/TO2
PULSE
GENERATOR
UVLO
VCC
400k
VCC
400k
T/V
Figure 5. Temperature Thresholds
Figure 6. Monitoring Internal Temperature with Two Overtemperature Thresholds
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.
The following design procedure can be used to size the
resistive divider.
1. Calculate Threshold Voltages:
VT1 =T1 4mV
KηACT
1.004
VT2 =T2 4mV
KηACT
1.004
where ηACT denotes the actual ideality factor if an ex ternal
sensor is used and T1 and T2 are the desired threshold
temperatures in degrees Kelvin.
2. Choose RTA to obtain the desired VT1 threshold for
a desired current through the resistive divider
(IREF):
RTA =VT1
IREF
3. Choose RTB to obtain the desired VT2 threshold:
RTB =VT2 VT1
IREF
2995 F05
VPTAT
RTC
RTB
RTA
VREF = 1.8V
1.8V
SLOPE = t

ACT
η
OT
200k T1T2L
VT2
VT1
O.8V
K
mV
LTC2995
14
2995f
APPLICATIONS INFORMATION
4. Finally RTC is determined by:
RTC =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 10A, the required values for RTA,
RTB and RTC can be calculated as:
RTA =1.332V
10µA =133.2k
RTB =1.452V 1.332V
10µA =12k
RTC =1.8V 1.452V
10µA =34.8k
Voltage Monitoring
In addition to temperature measurement, the LTC2995
features a low power dual voltage monitoring circuit. Each
voltage monitor has two inputs (VH1/VL1 and VH2/VL2)
for detecting undervoltage and overvoltage conditions. If
either VH1 or VH2 falls below 0.5V (typical), the LTC2995
communicates an undervoltage condition by pulling UV
low. Similar, an overvoltage condition is flagged by pulling
OV low if either VL1 or VL2 rises above 0.5V.
When configured to monitor a positive voltage Vn using
the 3-resistor circuit configuration shown in Figure 5,
VHn will be connected to the high side tap of the resistive
divider and VLn will be connected to the low side tap of
the resistive divider.
Voltage Monitor Design Procedure
The following 3-step design procedure selects appropriate
resistances to obtain the desired UV and OV trip points
for the voltage monitor circuit in Figure 7.
For supply monitoring, Vn is the desired nominal operat-
ing voltage, In is the desired nominal current through the
resistive divider, VOV is the desired overvoltage trip point,
and VUV is the desired undervoltage trip point.
1. RA is chosen to set the desired trip point for the
overvoltage monitor:
RA=0.5V
IN
VN
VOV
(1)
2. Once RA is known, RB is chosen to set the desired
trip point for the undervoltage monitor:
RB=0.5V
IN
VN
VUV
–RA
(2)
3. Once, RA and RB are known, RC is determined by:
RC=VN
IN
–RA–R
B
(3)
Voltage Monitor Example
A typical voltage monitor application is shown in Figure 2.
The monitored voltage is a 5V ±10% supply. Nominal
current in the resistive divider is 10µA.
1. Find RA to set the OV trip point of the monitor:
RA=0.5V
10µA 5V
5.5V 45.3k
Figure 7. 3-Resistor Positive UV/OV Monitoring
+
+
+
0.5V
LTC2995
UVn
VHn
RC
RB
RA
2995 F07
Vn
VLn
OVn
LTC2995
15
2995f
APPLICATIONS INFORMATION
2. Find RB to set the UV trip point of the monitor:
RB=0.5V
10µA 5V
4.5V 453 10k
3. Determine RC to complete the design:
RC=5V
10µA –453Ω 100Ω≈442k
Power-Up and Undervoltage Lockout
As soon as V
CC reaches approximately 1V during
power-up, the OV as well as TO1 and TO2 we ak l y p ul l t o VCC
while the UV output asserts low indicating an undervolt-
age lockout condition. Above VCC = 2V (typical), the VH
and VL inputs take control. Once both VH inputs and VCC
are valid, an internal timer is started. After an adjustable
delay time, UV weakly pulls high.
When VCC falls below 1.9V, the LTC2995 indicates again
an undervoltage lockout (UVLO) condition by pulling low
UV while OV is cleared.
Threshold Accuracy
Reset threshold accuracy is important in a supply sensitive
system. Ideally, such a system would only reset if supply
voltages fell outside the exact threshold for a specified
margin. All LTC2995 VHn/VLn inputs have a relative
threshold accuracy of ±1.5% over the full operating
temperature range. For example, when the LTC2995 is
configured to monitor a 5V input with a 10% tolerance,
the desired UV trip point is 4.5V. Because of the ±1.5%
relative accuracy of the LTC2995, the UV trip point can be
anywhere between 4.433V and 4.567V which is 4.5V ±1.5%.
Likewise, the accuracy of the resistances chosen for RA,
RB, and RC can affect the UV and OV trip points as well.
Using the previous example, if the resistances used to set
the UV trip point have 1% accuracy, the UV trip range can
grow to between 4.354V and 4.650V. This is illustrated in
the following calculations.
The UV trip point is given as:
VUV =0.5V t1+RC
RA+RB
The two extreme conditions, with a relative accuracy of
1.5% and resistance accuracy of 1%, result in:
VUV(MIN) =0.5V t0.985 t1+RCt0.99
(RA+RB)t1.01
and
VUV(MAX) =0.5V t1.015 t1+RCt1.01
(RA+RB)t0.99
For a desired trip point of 4.5V,
RC
RA+RB
=8
Therefore,
VUV(MIN) =0.5V t0.985 t1+80.99
1.01 =4.3545V
and
VUV(MAX) =0.5V t1.015 t1+81.01
0.99 =4.650V
Glitch Immunity
In any supervisory application, noise on the monitored DC
voltage can cause spurious resets. To solve this problem
without adding hysteresis to the VH/VL comparators, which
would add error to the trip voltage, the LTC2995 lowpass
filters the output of the comparator. This filter causes the
output of the comparator to be integrated before assert-
ing the UV or OV logic. Any transient at the input of the
comparator must be of sufficient magnitude and duration
before the comparator will trigger the output logic. The
Typical Performance Characteristics section shows a graph
of the Typical Transient Duration vs Comparator Overdrive.
In temperature monitoring, the voltage at VPTAT must
exceed a threshold for five consecutive temperature up-
date intervals before the respective TO pin is pulled low.
Once the VPTAT voltage crosses back the threshold with
an additional 20mV of hysteresis, the respective TO pin
is released after a single update interval and an additional
delay adjustable by the capacitor on TMR.
LTC2995
16
2995f
Timing of Alert Outputs
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.
A voltage monitoring example: When any VH drops below
its threshold, the UV pin asserts low. When all VH inputs
recover above their thresholds, the output timer starts. If
all inputs remain above their thresholds when the timer
finishes, the UV pin weakly pulls high. However, if any
input falls below its threshold during this timeout period,
the timer resets and restarts when all inputs are again
above the thresholds.
A temperature monitoring example: Tying PS to VCC
configures TO2 as overtemperature output. In case of
an overtemperature condition pin TO2 asserts low. The
output timer starts when the temperature crosses back
below the threshold minus the temperature hysteresis If
the temperature remains below the threshold, the timer
finishes and pin TO2 releases high.
Selecting the Timing Capacitor
The timeout period (tUOTO) for the LTC2995 is adjustable in
order to accommodate a variety of applications. Connect-
ing a capacitor, CTMR, between the TMR pin and ground
sets the timeout period. The value of capacitor needed for
a particular timeout period is:
CTMR =tUOTO –0.5ms
8[ms / nF]
The Reset Timeout Period vs Capacitance graph found in
the Typical Performance Characteristics section shows the
desired delay time as a function of the value of the timer
capacitor that should be used. Leaving the TMR pin open
with no external capacitor generates a timeout period of
approximately 500s. For long timeout periods, the only
limitation is the availability of a large value capacitor with
low leakage. Capacitor leakage current must not exceed
the minimum TMR charging current of 1.5A.
Tying the TMR pin to VCC will bypass the timeout period
and no delay will occur.
Digital Output Characteristics
The DC characteristics of the UV, OV, TO1 and TO2 pull-up
and pull-down strength are shown in the Typical Perfor-
mance Characteristics section. Each pin has a weak 400k
internal pull-up to VCC and a strong pull-down to ground
and can be pulled above VCC.
This arrangement allows these pins to have open-drain
behavior while possessing several other beneficial char-
acteristics. The weak pull-up eliminates the need for an
external pull-up resistor when the rise time on the pin is
not critical. On the other hand, the open drain configuration
allows for wired-OR connections and can be useful when
more than one signal needs to pull-down on the output.
At VCC = 1V, the weak pull-up current is barely turned on.
Therefore, an external pull-up resistor of no more than
100k is recommended on the pin if the state and pull-up
strength of the pin is crucial at very low VCC.
Note however, by adding an external pull-up resistor, the
pull-up strength on the pin is increased. Therefore, if it
is connected in a wired-OR connection, the pull-down
strength of any single device needs to accommodate this
additional pull-up strength.
Output Rise and Fall Time Estimation
The UV, OV, TO1 and TO2 outputs have strong pull-down
capability. The following formula estimates the output fall
time (90% to 10%) for a particular external load capaci-
tance (CLOAD):
t
FALL ≈ 2.2 • RPD • CLOAD
where RPD is the on-resistance of the internal pull-down
transistor estimated to be typically 40 at VDD > 1V and
at room temperature (25°C), and CLOAD is the external
load capacitance on the pin. Assuming a 150pF load
capacitance, the fall time is about 13ns. The rise time on
the UV, OV, TO1 and TO2 pins is limited by a 400k pull-up
resistance to VDD. A similar formula estimates the output
rise time (10% to 90%):
t
RISE ≈ 2.2 • RPU • CLOAD
where RPU is the pull-up resistance.
APPLICATIONS INFORMATION
LTC2995
17
2995f
±10% Voltage Monitor (1.8V and 2.5V) and Internal/Remote Overtemperature Monitor
TYPICAL APPLICATIONS
±20% Voltage Monitor (12V and 5V) and 0°C to 70°C Internal UT/OT Monitoring with Common
Temperature and Powergood LED
POWER
SUPPLIES
TEMPERATURE AND
POWER GOOD LED
VH1
VL1
VH2
VL2
D+
D
LTC2995
442k
113k
12V
5V
41.2k
2995 TA03
VT1VT2
43k 28k 110k
OT T > 70°C
UT T < 0°C
+20%
–20%
GND TMRVREF
4.12k
2.15k
21.5k
VPTAT
TO2
TO1
OV
UV
VCC
PS
DS
0.1µF 2.15k
VH1
VL1
VH2
VL2
D+
D
LTC2995
194k
124k
2.5V
1.8V
45.3k
2995 TA02
VT1VT2
20k 20k 140k
OT T > 125°C FOR EXTERNAL SENSOR
MMBT390
OT T > 75°C FOR INTERNAL SENSOR
+10%
–10%
GND TMRVREF
45.3k
10.2k
10.2k
VPTAT
TO2
TO1
OV
UV
VCC
PS
DS
5nF
470pF
0.1µF
POWER
SUPPLIES
LTC2995
18
2995f
TYPICAL APPLICATIONS
Celsius Thermometer and ±10% Voltage Monitor (1.8V and 2.5V)
±10% Voltage Monitor (12V and 5V) and –20°C to 70°C Internal UT/OT Monitor with
Manual Undervoltage Reset Button
POWER
SUPPLIES
VH1
VL1
VH2
VL2
D+
D
LTC2995
44.2k
115k
12V
5V
4.53k VT1VT2
43k 36k 102k
OT T > 70°C
UT T < –20°C
+10%
–10%
GND TMRVREF
4.53k
1k
MANUAL
RESET BUTTON
(NORMALLY OPEN)
1k
VPTAT
TO2
TO1
OV
UV
VCC
PS
DS
0.1µF
SYSTEM
RESET
2995 TA05
POWER
SUPPLIES
VH1
VL1
VH2
VL2
D+
D
LTC2995
194k
124k
2.5V
1.8V
45.3k
2995 TA04
VT1VT2
+10%
–10%
1.8V 100k
1k
4mV/K
GND TMR TO2 TO1
45.3k
10.2k
10.2k
VPTAT
OV
UV
VCC
PS
DS
0.1µF
5nF
470pF MMBT3904
VREF
+
62k
143k 1µF
0.1µF
LTC1150
5V
–5V
10mV/°C
0V AT 0°C
150k 1.8k
LTC2995
19
2995f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibilit y is assumed for its use. Linear Technology Corporation makes no representa-
t i o n t h a t t h e i n t e r c o n n e c t i o n o f i t s c i r c u i t s a s d e s c r i b e d h e r e i n w i l l n o t i n f r i n g e o n e x i s t i n g p a t e n t r i g h t s .
PACKAGE DESCRIPTION
3.00 ± 0.10
(4 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
1.65 ± 0.05
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
PIN 1
TOP MARK
(NOTE 6)
0.40 ± 0.10
BOTTOM VIEW—EXPOSED PAD
1.65 ± 0.10
(4-SIDES)
0.75 ± 0.05 R = 0.115
TYP
R = 0.05
TYP
0.20 ± 0.05
1
PIN 1 NOTCH
R = 0.20 TYP
OR 0.25 × 45°
CHAMFER
19 20
2
0.40 BSC
0.200 REF
2.10 ± 0.05
3.50 ± 0.05
(4 SIDES)
0.70 ±0.05
0.00 – 0.05
(UD20) QFN 0306 REV A
0.20 ±0.05
0.40 BSC
PACKAGE
OUTLINE
UD Package
20-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1720 Rev A)
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
LTC2995
20
2995f
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2012
LT 0412 • PRINTED IN USA
RELATED PARTS
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
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LTC2900 Programmable Quad Supply Monitor Adjustable RESET, 10-Lead MSOP and 3mm × 3mm 10-Lead DFN
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One Adjustable
Separate VCC Pin, RST/RST Outputs
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One Adjustable
Separate VCC, Adjustable Reset Timer
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Adjustable)
8-Lead SOT-23 and DDB Packages
LTC2909 Prevision Dual Input UV, OV and Negative Voltage
Monitor
2 ADJ Inputs, Monitors Negative Voltages
LTC2912 Single UV/OV Positive Voltage Monitor Separate VCC Pin, 8-Lead TSOT and 3mm × 2mm DFN Packages
LTC2913 Dual UV/OV Positive Voltage Monitor Separate VCC Pin, 10-Lead MSOP and 3mm × 3mm DFN Packages
LTC2914 Quad UV/OV Positive/Negative Voltage Monitor Separate VCC Pin, 16-Lead SSOP and 5mm × 2mm DFN Packages
Dual OV/UV ±10% Supply and 75°C/125°C OT/OT Remote Temperature Monitor
ASIC/
CPU/
FPGA
VH1
VL1
VH2
VL2
D+
D
LTC2995
194k
64.4k
2.5V
1.2V
45.3k
2995 TA06
VT1 VT2 VREF
+10%
–10%
GNDTMR
45.3k
10.2k
10.2k
VPTAT
TO2
TO1
OV
UV
VCC
PS
DS
0.1µF
5nF 140k 20k 20k
470pF
OT T > 125°C
OT T > 75°C
A/D