1 C Digital Temperature Sensor with Series Resistance

NVT211
+15C Temperature Monitor
with Series Resistance
Cancellation
The NVT211 is a dual-channel digital thermometer and
undertemperature/overtemperature alarm, intended for use in thermal
management systems. It is register-compatible with the NCT1008 and
NCT72. A feature of the NVT211 is series resistance cancellation,
where up to 1.5 kW (typical) of resistance in series with the temperature
monitoring diode can be automatically cancelled from the temperature
result, allowing noise filtering. The NVT211 has a configurable ALERT
output and an extended, switchable temperature measurement range.
The NVT211 can measure the temperature of a remote thermal diode
accurate to ±1°C and the ambient temperature accurate to ±3°C. The
temperature measurement range defaults to 0°C to +127°C, compatible
with the NCT1008 and NCT72, but it can be switched to a wider
measurement range of −64°C to +191°C.
The NVT211 communicates over a 2-wire serial interface,
compatible with system management bus (SMBus/I2C) standards. The
default SMBus/I2C address of the NVT211 is 0x4C. An NVT211D is
available with an SMBus/I2C address of 0x4D. This is useful if more
than one NVT211 is used on the same SMBus/I2C.
An ALERT output signals when the on-chip or remote temperature is
out of range. The THERM output is a comparator output that allows
on/off control of a cooling fan. The ALERT output can be reconfigured
as a second THERM output, if required.
The NVT211 has been through Automotive Qualification according to
AEC−Q100 Grade 1 standards.
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WDFN8
MT SUFFIX
CASE 511AT
PIN ASSIGNMENT
1
VDD
•
•
•
•
•
•
•
•
•
On-chip and Remote Temperature Sensor
0.25°C Resolution/1°C Accuracy on Remote Channel
1°C Resolution/1°C Accuracy on Local Channel
Series Resistance Cancellation Up to 1.5 kW
Extended, Switchable Temperature Measurement Range
0°C to +127°C (Default) or –64°C to +191°C
Register-compatible with NCT1008 and NCT72
2-wire SMBus/I2C Serial Interface with SMBus Alert Support
Programmable Over/Undertemperature Limits
Offset Registers for System Calibration
Up to Two Overtemperature Fail-safe THERM Outputs
2 × 2 WDFN8 Package
240 mA Operating Current, 5 mA Standby Current
Automotive Qualification According to AEC−Q100, Grade 1
These are Pb−Free Devices
SDATA
ALERT/
THERM2
GND
D−
THERM
(Top View)
MARKING DIAGRAM
1
Features
•
•
•
•
•
SCLK
D+
NxMG
G
WDFN8
Nx
M
G
= Device Code (Where x = C or D)
= Date Code
= Pb-Free Package
(Note: Microdot may be in either location)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 18 of this data sheet.
Applications
• Automotive
• Embedded Systems
© Semiconductor Components Industries, LLC, 2013
December, 2013 − Rev. 0
1
Publication Order Number:
NVT211/D
NVT211
D−
3
ANALOG
MUX
LOCAL TEMPERATURE
VALUE REGISTER
LOCAL TEMPERATURE
LOW-LIMIT REGISTER
A-TO-D
CONVERTER
BUSY
RUN/STANDBY
LOCAL TEMPERATURE
HIGH-LIMIT REGISTER
REMOTE TEMPERATURE
VALUE REGISTER
DIGITAL MUX
2
ADDRESS POINTER
REGISTER
LIMIT COMPARATOR
D+
CONVERSION RATE
REGISTER
DIGITAL MUX
ON-CHIP
TEMPERATURE
SENSOR
REMOTE TEMPERATURE
LOW-LIMIT REGISTER
REMOTE TEMPERATURE
HIGH-LIMIT REGISTER
LOCAL THERM
LIMIT REGISTERS
REMOTE OFFSET
REGISTER
EXTERNAL THERM
LIMIT REGISTERS
CONFIGURATION
REGISTERS
EXTERNAL DIODE OPEN-CIRCUIT
INTERRUPT
MASKING
STATUS REGISTER
NVT211
SMBus/I2C INTERFACE
1
5
7
8
4
VDD
GND
SDATA
SCLK
THERM
6
ALERT/THERM2
Figure 1. Functional Block Diagram
Table 1. PIN ASSIGNMENT
Pin No.
Mnemonic
1
VDD
Positive Supply, 2.8 V to 3.6 V.
Description
2
D+
Positive Connection to Remote Temperature Sensor.
3
D−
Negative Connection to Remote Temperature Sensor.
4
THERM
5
GND
6
ALERT/THERM2
7
SDATA
Logic Input/Output, SMBus/I2C Serial Data. Open-drain Output. Requires pullup resistor.
8
SCLK
Logic Input, SMBus/I2C Serial Clock. Requires pullup resistor.
Open-drain Output. Can be used as an overtemperature shutdown pin. Requires pullup resistor.
Supply Ground Connection.
Open-drain Logic Output Used as Interrupt or SMBus ALERT. This can also be configured as a
second THERM output. Requires pullup resistor to VDD.
Table 2. ABSOLUTE MAXIMUM RATINGS
Parameter
Positive Supply Voltage (VDD) to GND
Rating
Unit
−0.3, +3.6
V
−0.3 to VDD + 0.3
V
D− to GND
−0.3 to +0.6
V
SCLK, SDATA, ALERT, THERM
−0.3 to +3.6
V
Input Current, SDATA, THERM
−1, +50
mA
±1
mA
1,500
V
150
°C
−65 to +150
°C
D+
Input Current, D−
ESD Rating, All Pins (Human Body Model)
Maximum Junction Temperature (TJ MAX)
Storage Temperature Range
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
NOTE: This device is ESD sensitive. Use standard ESD precautions when handling.
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NVT211
Table 3. SMBus/I2C TIMING SPECIFICATIONS (Note 1)
1.
2.
3.
4.
Parameter
Limit at TMIN and TMAX
Unit
fSCLK
400
kHz max
Description
−
tLOW
1.3
ms min
Clock Low Period, between 10% Points
tHIGH
0.6
ms min
Clock High Period, between 90% Points
tR
300
ns max
Clock/Data Rise Time
tF
300
ns max
Clock/Data Fall Time
tSU; STA
600
ns min
Start Condition Setup Time
tHD; STA (Note 2)
600
ns min
Start Condition Hold Time
tSU; DAT (Note 3)
100
ns min
Data Setup Time
tSU; STO (Note 4)
600
ns min
Stop Condition Setup Time
tBUF
1.3
ms min
Bus Free Time between Stop and Start Conditions
Guaranteed by design, but not production tested.
Time from 10% of SDATA to 90% of SCLK.
Time for 10% or 90% of SDATA to 10% of SCLK.
Time for 90% of SCLK to 10% of SDATA.
t LOW
tF
t HD; STA
tR
SCLK
t HD; STA
t HD; DAT
t HIGH
t SU; STA
t SU; DAT
t SU; STO
SDATA
t BUF
STOP START
START
Figure 2. Serial Bus Timing
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STOP
NVT211
Table 4. ELECTRICAL CHARACTERISTICS (TA = −40°C to +125°C, VDD = 2.8 V to 3.6 V, unless otherwise noted)
Conditions
Parameter
Min
Typ
Max
Unit
Power Supply
2.8
3.30
3.6
V
Average Operating Supply Current, IDD
0.0625 Conversions/Sec Rate (Note 1, 2)
Standby Mode
−
−
240
5.0
350
30
mA
Undervoltage Lockout Threshold
VDD input, disables ADC, rising edge
−
2.55
−
V
1.0
−
2.56
V
Supply Voltage, VDD
Power-on Reset Threshold
Temperature-to-Digital Converter
Local Sensor Accuracy
3.0 V to 3.6 V
0°C ≤ TA ≤ +70°C
0°C ≤ TA ≤ +85°C
−
−
−
−
±1.0
±1.5
°C
Local Sensor Accuracy
2.8 V to 3.6 V
−20°C ≤ TA ≤ +110°C
−
−
±2.5
°C
Resolution
−
1.0
−
°C
Remote Diode Sensor Accuracy
3.0 V to 3.6 V
0°C ≤ TA ≤ +70°C, −55°C ≤ TD (Note 3) ≤ +150°C
0°C ≤ TA ≤ +85°C, −55°C ≤ TD (Note 3) ≤ +150°C
−40°C ≤ TA ≤ +100°C, −55°C ≤ TD (Note 3) ≤ +150°C
−
−
−
−
−
−
±1.0
±1.5
±2.5
°C
Remote Diode Sensor Accuracy
2.8 V to 3.6 V
0°C ≤ TA ≤ +70°C, −20°C ≤ TD ≤ +110°C
−20°C ≤ TA ≤ +110°C, TD = +40°C
−
−
−
−
±1.5
±2.25
°C
−
0.25
−
°C
Resolution
Remote Sensor Source Current
High Level (Note 3)
Middle Level (Note 3)
Low Level (Note 3)
−
−
−
220
82
13.5
−
−
−
mA
Conversion Time
From Stop Bit to Conversion Complete, One-shot
Mode with Averaging Switched On
−
40
52
ms
One-shot Mode with Averaging Off
(that is, Conversion Rate = 16-, 32-, or
64-conversions per Second)
−
6.0
8.0
ms
Resistance Split Evenly on both the D+ and D– Inputs
−
1.5
−
kW
Maximum Series Resistance Cancelled
Open-drain Digital Outputs (THERM, ALERT/THERM2)
Output Low Voltage, VOL
IOUT = −6.0 mA
−
−
0.4
V
High Level Output Leakage Current, IOH
VOUT = VDD
−
0.1
1.0
mA
Logic Input High Voltage, VIH SCLK, SDATA
1.4
−
−
V
Logic Input Low Voltage, VIL SCLK, SDATA
−
−
0.8
V
Hysteresis
−
500
−
mV
SDA Output Low Voltage, VOL
−
−
0.4
mA
SMBus/I2C Interface (Note 4 and 5)
Logic Input Current, IIH, IIL
−1.0
−
+1.0
mA
SMBus/I2C Input Capacitance,
SCLK, SDATA
−
5.0
−
pF
SMBus/I2C Clock Frequency
−
−
400
kHz
User Programmable
−
25
64
ms
Master Clocking in Data
−
−
1.0
ms
SMBus/I2C
Timeout (Note 6)
SCLK Falling Edge to SDATA Valid Time
1.
2.
3.
4.
5.
6.
See Table 8 for information on other conversion rates.
THERM and ALERT pulled to VDD.
Guaranteed by characterization, but not production tested.
Guaranteed by design, but not production tested.
See SMBus/I2C Timing Specifications section for more information.
Disabled by default. Detailed procedures to enable it are in the Serial Bus Interface section of the datasheet.
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NVT211
TYPICAL PERFORMANCE CHARACTERISTICS
3.5
DEV 1
DEV 2
DEV 3
DEV 4
DEV 5
DEV 6
DEV 7
3.0
2.5
2.0
DEV 8
DEV 9
DEV 10
DEV 11
DEV 12
DEV 13
DEV 14
DEV 15
DEV 16
MEAN
HIGH 4R
LOW 4R
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR (°C)
3.5
1.5
1.0
0.5
0
−0.5
−1.0
−50
0
50
100
DEV 1
DEV 2
DEV 3
DEV 4
DEV 5
DEV 6
DEV 7
3.0
2.5
2.0
1.0
0.5
0
−0.5
0
TEMPERATURE (°C)
150
0
5
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR (°C)
100
Figure 4. Remote Temperature Error vs. Actual
Temperature
10
D+ To GND
0
−5
−10
D+ To VDD
−15
−20
1
10
−2
−4
−6
−8
−10
DEV 2
−14
DEV 4
−16
−18
100
DEV 3
−12
0
5
LEAKAGE RESISTANCE (MW)
1000
15
20
25
Figure 6. Temperature Error vs. D+/D− Capacitance
422
DEV 2BC
900
10
CAPACITANCE (nF)
Figure 5. Temperature Error vs. D+/D− Leakage
Resistance
420
800
DEV 2BC
418
700
600
500
IDD (mA)
IDD (mA)
50
TEMPERATURE (°C)
Figure 3. Local Temperature Error vs. Temperature
−25
DEV 15
DEV 16
HIGH 4R
LOW 4R
1.5
−1.0
−50
150
DEV 8
DEV 9
DEV 10
DEV 11
DEV 12
DEV 13
DEV 14
DEV 4BC
400
DEV 3BC
300
416
414
DEV 3BC
DEV 4BC
412
200
410
100
0
0.01
0.1
1
10
408
3.0
100
CONVERSION RATE (Hz)
3.1
3.2
3.3
3.4
3.5
3.6
VDD (V)
Figure 7. Operating Supply Current vs.
Conversion Rate
Figure 8. Operating Supply Current vs. Voltage
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NVT211
TYPICAL PERFORMANCE CHARACTERISTICS (Cont’d)
4.4
35
DEV 2BC
DEV 3BC
DEV 4BC
DEV 2
4.2
30
25
DEV 3
3.8
ISTBY (mA)
IDD (mA)
4.0
DEV 4
3.6
20
15
3.4
10
3.2
5
3.0
3.0
3.1
3.2
3.3
3.4
3.5
0
3.6
1
10
VDD (V)
Figure 9. Standby Supply Current vs. Voltage
80
20
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR (°C)
1000
Figure 10. Standby Supply Current vs. Clock
Frequency
25
100 mV
15
10
50 mV
20 mV
5
0
100
FSCL (kHz)
0
100
200
300
400
500
70
50
40
30
50 mV
20
10
20 mV
0
−10
600
100 mV
60
0
100
200
Figure 11. Temperature Error vs. Common-mode
Noise Frequency
TEMPERATURE ERROR (°C)
50
40
30
20
10
0
400
500
600
Figure 12. Temperature Error vs. Differential-mode
Noise Frequency
60
0
300
NOISE FREQUENCY (MHz)
NOISE FREQUENCY (MHz)
500
1000
1500
2000
SERIES RESISTANCE (W)
Figure 13. Temperature Error vs. Series Resistance
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NVT211
Theory of Operation
Temperature Measurement Method
The NVT211 is a local and remote temperature sensor and
over/under temperature alarm, with the added ability to
automatically cancel the effect of 1.5 kW (typical) of
resistance in series with the temperature monitoring diode.
When the NVT211 is operating normally, the on-board ADC
operates in a free running mode. The analog input
multiplexer alternately selects either the on-chip
temperature sensor to measure its local temperature or the
remote temperature sensor. The ADC digitizes these signals
and the results are stored in the local and remote temperature
value registers.
The local and remote measurement results are compared
with the corresponding high, low, and THERM temperature
limits, stored in eight on-chip registers. Out-of-limit
comparisons generate flags that are stored in the status
register. A result that exceeds the high temperature limit or
the low temperature limit causes the ALERT output to
assert. The ALERT output also asserts if an external diode
fault is detected. Exceeding the THERM temperature limits
causes the THERM output to assert low. The ALERT output
can be reprogrammed as a second THERM output.
The limit registers are programmed and the device
controlled and configured via the serial SMBus/I2C. The
contents of any register are also read back via the
SMBus/I2C.
Control and configuration functions consist of switching
the device between normal operation and standby mode,
selecting the temperature measurement range, masking or
enabling the ALERT output, switching Pin 6 between
ALERT and THERM2, and selecting the conversion rate.
A simple method of measuring temperature is to exploit
the negative temperature coefficient of a diode, measuring
the base emitter voltage (VBE) of a transistor operated at
constant current. However, this technique requires
calibration to null the effect of the absolute value of VBE,
which varies from device to device.
The technique used in the NVT211 measures the change
in VBE when the device operates at three different currents.
Previous devices used only two operating currents, but it is
the use of a third current that allows automatic cancellation
of resistances in series with the external temperature sensor.
Figure 14 shows the input signal conditioning used to
measure the output of an external temperature sensor. This
figure shows the external sensor as a substrate transistor, but
it can equally be a discrete transistor. If a discrete transistor
is used, the collector is not grounded but is linked to the base.
To prevent ground noise interfering with the measurement,
the more negative terminal of the sensor is not referenced to
ground, but is biased above ground by an internal diode at
the D− input. C1 may be added as a noise filter
(a recommended maximum value of 1,000 pF). However, a
better option in noisy environments is to add a filter, as
described in the Noise Filtering section. See the Layout
Considerations section for more information on C1.
To measure DVBE, the operating current through the
sensor is switched among three related currents. As shown
in Figure 14, N1 × I and N2 × I are different multiples of the
current, I. The currents through the temperature diode are
switched between I and N1 × I, giving DVBE1; and then
between I and N2 × I, giving DVBE2. The temperature is
then calculated using the two DVBE measurements. This
method also cancels the effect of any series resistance on the
temperature measurement.
The resulting DVBE waveforms are passed through a
65 kHz low-pass filter to remove noise and then to a
chopper-stabilized amplifier. This amplifies and rectifies the
waveform to produce a dc voltage proportional to DVBE.
The ADC digitizes this voltage producing a temperature
measurement. To reduce the effects of noise, digital filtering
is performed by averaging the results of 16 measurement
cycles for low conversion rates. At rates of 16-, 32-, and
64-conversions/second, no digital averaging occurs.
Signal conditioning and measurement of the internal
temperature sensor are performed in the same manner.
Series Resistance Cancellation
Parasitic resistance to the D+ and D− inputs to the
NVT211, seen in series with the remote diode, is caused by
a variety of factors, including PCB track resistance and track
length. This series resistance appears as a temperature offset
in the remote sensor’s temperature measurement. This error
typically causes a 0.5°C offset per ohm of parasitic
resistance in series with the remote diode.
The NVT211 automatically cancels the effect of this
series resistance on the temperature reading, giving a more
accurate result, without the need for user characterization of
this resistance. The NVT211 is designed to automatically
cancel typically up to 1.5 kW of resistance. By using an
advanced temperature measurement method, this process is
transparent to the user. This feature permits resistances to be
added to the sensor path to produce a filter, allowing the part
to be used in noisy environments. See the section on Noise
Filtering for more details.
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NVT211
I
N1 × I
N2 × I
IBIAS
VDD
D+
REMOTE
SENSING
TRANSISTOR
VOUT+
To ADC
C1*
D−
VOUT−
BIAS
DIODE
LOW-PASS FILTER
fC = 65 kHz
*CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1,000 pF MAX.
Figure 14. Input Signal Conditioning
Temperature Measurement Results
The extended temperature range is selected by setting
Bit 2 of the configuration register to 1. The temperature
range is 0°C to 127°C when Bit 2 equals 0. A valid result is
available in the next measurement cycle after changing the
temperature range.
In extended temperature mode, the upper and lower
temperature that can be measured by the NVT211 is limited
by the remote diode selection. The temperature registers can
have values from −64°C to +191°C. However, most
temperature sensing diodes have a maximum temperature
range of −55°C to +150°C. Above +150°C, they may lose
their semiconductor characteristics and approximate
conductors instead. This results in a diode short. In this case,
a read of the temperature result register gives the last good
temperature measurement. Therefore, the temperature
measurement on the external channel may not be accurate
for temperatures that are outside the operating range of the
remote sensor.
It should be noted that although both local and remote
temperature measurements can be made while the part is in
extended temperature mode, the NVT211 itself should not
be exposed to temperatures greater than those specified in
the absolute maximum ratings section. Further, the device is
only guaranteed to operate as specified at ambient
temperatures from −40°C to +120°C.
The results of the local and remote temperature
measurements are stored in the local and remote temperature
value registers and compared with limits programmed into
the local and remote high and low limit registers.
The local temperature value is in Register 0x00 and has a
resolution of 1°C. The external temperature value is stored
in two registers, with the upper byte in Register 0x01 and the
lower byte in Register 0x10. Only the two MSBs in the
external temperature low byte are used giving the external
temperature measurement a resolution of 0.25°C. Table 5
lists the data format for the external temperature low byte.
Table 5. EXTENDED TEMPERATURE RESOLUTION
(REMOTE TEMPERATURE LOW BYTE)
Extended Resolution
Remote Temperature
Low Byte
0.00°C
0 000 0000
0.25°C
0 100 0000
0.50°C
1 000 0000
0.75°C
1 100 0000
When reading the full external temperature value, read the
LSB first. This causes the MSB to be locked (that is, the
ADC does not write to it) until it is read. This feature ensures
that the results read back from the two registers come from
the same measurement.
Temperature Data Format
The NVT211 has two temperature data formats. When the
temperature measurement range is from 0°C to 127°C
(default), the temperature data format for both internal and
external temperature results is binary. When the
measurement range is in extended mode, an offset binary
data format is used for both internal and external results.
Temperature values are offset by 64°C in the offset binary
data format. Examples of temperatures in both data formats
are shown in Table 6.
Temperature Measurement Range
The temperature measurement range for both internal and
external measurements is, by default, 0°C to +127°C.
However, the NVT211 can be operated using an extended
temperature range. The extended measurement range is
−64°C to +191°C. Therefore, the NVT211 can be used to
measure the full temperature range of an external diode,
from −55°C to +150°C.
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NVT211
register. It is to this register address that the second byte of
a write operation is written, or to which a subsequent read
operation is performed.
The power-on default value of the address pointer register
is 0x00. Therefore, if a read operation is performed
immediately after power-on, without first writing to the
address pointer, the value of the local temperature is returned
because its register address is 0x00.
Table 6. TEMPERATURE DATA FORMAT
(TEMPERATURE HIGH BYTE)
Offset Binary
(Note 1)
Temperature
Binary
–55°C
0 000 0000
(Note 2)
0 000 1001
0°C
0 000 0000
0 100 0000
+1°C
0 000 0001
0 100 0001
+10°C
0 000 1010
0 100 1010
+25°C
0 001 1001
0 101 1001
+50°C
0 011 0010
0 111 0010
+75°C
0 100 1011
1 000 1011
+100°C
0 110 0100
1 010 0100
+125°C
0 111 1101
1 011 1101
+127°C
0 111 1111
1 011 1111
+150°C
0 111 1111
(Note 3)
1 101 0110
Temperature Value Registers
The NVT211 has three registers to store the results of local
and remote temperature measurements. These registers can
only be written to by the ADC and can be read by the user
over the SMBus/I2C. The local temperature value register is
at Address 0x00.
The external temperature value high byte register is at
Address 0x01, with the low byte register at Address 0x10.
The power-on default for all three registers is 0x00.
Configuration Register
1. Offset binary scale temperature values are offset by 64°C.
2. Binary scale temperature measurement returns 0°C for all
temperatures < 0°C.
3. Binary scale temperature measurement returns 127°C for all
temperatures > 127°C.
The configuration register is Address 0x03 at read and
Address 0x09 at write. Its power-on default is 0x00. Only
four bits of the configuration register are used. Bit 0, Bit 1,
Bit 3, and Bit 4 are reserved; the user does not write to them.
Bit 7 of the configuration register masks the ALERT
output. If Bit 7 is 0, the ALERT output is enabled. This is the
power-on default. If Bit 7 is set to 1, the ALERT output is
disabled. This applies only if Pin 6 is configured as ALERT.
If Pin 6 is configured as THERM2, then the value of Bit 7
has no effect.
If Bit 6 is set to 0, which is power-on default, the device
is in operating mode with ADC converting. If Bit 6 is set to
1, the device is in standby mode and the ADC does not
convert. The SMBus/I2C does, however, remain active in
standby mode; therefore, values can be read from or written
to the NVT211 via the SMBus. The ALERT and THERM
outputs are also active in standby mode. Changes made to
the registers in standby mode that affect the THERM or
ALERT outputs cause these signals to be updated.
Bit 5 determines the configuration of Pin 6 on the
NVT211. If Bit 5 is 0 (default), then Pin 6 is configured as
an ALERT output. If Bit 5 is 1, then Pin 6 is configured as
a THERM2 output. Bit 7, the ALERT mask bit, is only
active when Pin 6 is configured as an ALERT output. If
Pin 6 is set up as a THERM2 output, then Bit 7 has no effect.
Bit 2 sets the temperature measurement range. If Bit 2 is
0 (default value), the temperature measurement range is set
between 0°C to +127°C. Setting Bit 2 to 1 sets the
measurement range to the extended temperature range
(−64°C to +191°C).
The user can switch between measurement ranges at any
time. Switching the range likewise switches the data format.
The next temperature result following the switching is
reported back to the register in the new format. However, the
contents of the limit registers do not change. It is up to the
user to ensure that when the data format changes, the limit
registers are reprogrammed as necessary. More information
on this is found in the Limit Registers section.
NVT211 Registers
The NVT211 contains 22, 8-bit registers in total. These
registers store the results of remote and local temperature
measurements, high and low temperature limits, and
configure and control the device. See the Address Pointer
Register section through the Consecutive ALERT Register
section of this data sheet for more information on the
NVT211 registers. Additional details are shown in Table 7
through Table 11. The entire register map is available in
Table 12.
Address Pointer Register
The address pointer register itself does not have, nor does
it require, an address because the first byte of every write
operation is automatically written to this register. The data
in this first byte always contains the address of another
register on the NVT211 that is stored in the address pointer
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NVT211
hysteresis register. All limit registers can be written to, and
read back over, the SMBus/I2C. See Table 12 for details of
the limit register addresses and their power-on default
values.
When Pin 6 is configured as an ALERT output, the high
limit registers perform a > comparison, while the low limit
registers perform a ≤ comparison. For example, if the high
limit register is programmed with 80°C, then measuring
81°C results in an out-of-limit condition, setting a flag in the
status register. If the low limit register is programmed with
0°C, measuring 0°C or lower results in an out-of-limit
condition.
Exceeding either the local or remote THERM limit asserts
THERM low. When Pin 6 is configured as THERM2,
exceeding either the local or remote high limit asserts
THERM2 low. A default hysteresis value of 10°C is
provided that applies to both THERM channels. This
hysteresis value can be reprogrammed to any value after
powerup (Register Address 0x21).
It is important to remember that the temperature limits
data format is the same as the temperature measurement data
format. Therefore, if the temperature measurement uses
default binary, then the temperature limits also use the
binary scale. If the temperature measurement scale is
switched, however, the temperature limits do not
automatically switch. The user must reprogram the limit
registers to the desired value in the correct data format. For
example, if the remote low limit is set at 10°C with the
default binary scale, the limit register value is 0000 1010b.
If the scale is switched to offset binary, the value in the low
temperature limit register needs to be reprogrammed to
0100 1010b.
Table 7. CONFIGURATION REGISTER BIT
ASSIGNMENTS
Bit
Name
Function
Power-on
Default
7
MASK1
0 = ALERT Enabled
1 = ALERT Masked
0
6
RUN/STOP
0 = Run
1 = Standby
0
5
ALERT/
THERM2
0 = ALERT
1 = THERM2
0
4, 3
Reserved
2
1, 0
0
Temperature
Range Select
0 = 0°C to 127°C
1 = Extended Range
0
Reserved
0
Conversion Rate Register
The conversion rate register is Address 0x04 at read and
Address 0x0A at write. The lowest four bits of this register
are used to program the conversion rate by dividing the
internal oscillator clock by 1, 2, 4, 8, 16, 32, 64, 128, 256,
512, or 1024 to give conversion times from 15.5 ms
(Code 0x0A) to 16 seconds (Code 0x00). For example, a
conversion rate of eight conversions per second means that
beginning at 125 ms intervals, the device performs a
conversion on the internal and the external temperature
channels.
The conversion rate register can be written to and read
back over the SMBus/I2C. The higher four bits of this
register are unused and must be set to 0. The default value
of this register is 0x08, giving a rate of 16 conversions per
second. Use of slower conversion times greatly reduces the
device power consumption.
Status Register
Table 8. CONVERSION RATE REGISTER CODES
Code
Conversion/Second
Time
0x00
0.0625
16 s
0x01
0.125
8s
0x02
0.25
4s
0x03
0.5
2s
0x04
1
1s
0x05
2
500 ms
0x06
4
250 ms
0x07
8
125 ms
0x08
16
62.5 ms
0x09
32
31.25 ms
0x0A
64
15.5 ms
0x0B to 0xFF
Reserved
−
The status register is a read-only register at Address 0x02.
It contains status information for the NVT211.
When Bit 7 of the status register is high, it indicates that
the ADC is busy converting. The other bits in this register
flag the out-of-limit temperature measurements (Bit 6 to
Bit 3, and Bit 1 to Bit 0) and the remote sensor open circuit
(Bit 2).
If Pin 6 is configured as an ALERT output, the following
applies: If the local temperature measurement exceeds its
limits, Bit 6 (high limit) or Bit 5 (low limit) of the status
register asserts to flag this condition. If the remote
temperature measurement exceeds its limits, then Bit 4
(high limit) or Bit 3 (low limit) asserts. Bit 2 asserts to flag
an open circuit condition on the remote sensor. These five
flags are NOR’ed together, so if any of them is high, the
ALERT interrupt latch is set and the ALERT output goes
low.
Reading the status register clears the five flags, Bit 6 to
Bit 2, provided the error conditions causing the flags to be
set have gone away. A flag bit can be reset only if the
corresponding value register contains an in-limit
measurement or if the sensor is good.
Limit Registers
The NVT211 has eight limit registers: high, low, and
THERM temperature limits for both local and remote
temperature measurements. The remote temperature high
and low limits span two registers each, to contain an upper
and lower byte for each limit. There is also a THERM
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NVT211
maximum is +127.75°C. The value in the offset register is
added to, or subtracted from, the measured value of the
remote temperature.
The offset register powers up with a default value of 0°C
and has no effect unless the user writes a different value to
it.
The ALERT interrupt latch is not reset by reading the
status register. It resets when the ALERT output has been
serviced by the master reading the device address, provided
the error condition has gone away and the status register flag
bits are reset.
When Flag 1 and/or Flag 0 are set, the THERM output
goes low to indicate that the temperature measurements are
outside the programmed limits. The THERM output does
not need to be reset, unlike the ALERT output. Once the
measurements are within the limits, the corresponding status
register bits are automatically reset and the THERM output
goes high. The user may add hysteresis by programming
Register 0x21. The THERM output is reset only when the
temperature falls to limit value minus the hysteresis value.
When Pin 6 is configured as THERM2, only the high
temperature limits are relevant. If Flag 6 and/or Flag 4 are
set, the THERM2 output goes low to indicate that the
temperature measurements are outside the programmed
limits. Flag 5 and Flag 3 have no effect on THERM2. The
behavior of THERM2 is otherwise the same as THERM.
Table 10. SAMPLE OFFSET REGISTER CODES
Name
7
BUSY
6
LHIGH
(Note 1)
1 when Local High Temperature Limit is
Tripped
5
LLOW
(Note 1)
1 when Local Low Temperature Limit is
Tripped
4
RHIGH
(Note 1)
1 when Remote High Temperature Limit
is Tripped
3
RLOW
(Note 1)
1 when Remote Low Temperature Limit
is Tripped
2
OPEN
(Note 1)
1 when Remote Sensor is an Open
Circuit
1
RTHRM
1 when Remote THERM Limit is Tripped
0
LTHRM
1 when Local THERM Limit is Tripped
0x11
0x12
−128°C
1000 0000
00 00 0000
−4°C
1111 1100
00 00 0000
−1°C
1111 1111
00 000000
−0.25°C
1111 1111
10 00 0000
0°C
0000 0000
00 00 0000
+0.25°C
0000 0000
01 00 0000
+1°C
0000 0001
00 00 0000
+4°C
0000 0100
00 00 0000
+127.75°C
0111 1111
11 00 0000
One-shot Register
Table 9. STATUS REGISTER BIT ASSIGNMENTS
Bit
Offset Value
The one-shot register is used to initiate a conversion and
comparison cycle when the NVT211 is in standby mode,
after which the device returns to standby. Writing to the
one-shot register address (0x0F) causes the NVT211 to
perform a conversion and comparison on both the internal
and the external temperature channels. This is not a data
register as such, and it is the write operation to Address 0x0F
that causes the one-shot conversion. The data written to this
address is irrelevant and is not stored.
Function
1 when ADC is Converting
Consecutive ALERT Register
The value written to this register determines how many
out-of-limit measurements must occur before an ALERT is
generated. The default value is that one out-of-limit
measurement generates an ALERT. The maximum value
that can be chosen is 4. The purpose of this register is to
allow the user to perform some filtering of the output. This
is particularly useful at the fastest three conversion rates,
where no averaging takes place. This register is at
Address 0x22.
1. These flags stay high until the status register is read or they are
reset by POR unless Pin 6 is configured as THERM2. Then, only
Bit 2 remains high until the status register is read or is reset by
POR.
Offset Register
Offset errors can be introduced into the remote
temperature measurement by clock noise or when the
thermal diode is located away from the hot spot. To achieve
the specified accuracy on this channel, these offsets must be
removed.
The offset value is stored as a 10-bit, twos complement
value in Register 0x11 (high byte) and Register 0x12 (low
byte, left justified). Only the upper two bits of Register 0x12
are used. The MSB of Register 0x11 is the sign bit. The
minimum, programmable offset is −128°C, and the
Table 11. CONSECUTIVE ALERT REGISTER CODES
NOTE:
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Register Value
Number of Out-of-limit
Measurements Required
yxxx 000x
1
yxxx 001x
2
yxxx 011x
3
yxxx 111x
4
x = don’t care bits, and y = SMBus timeout bit.
Default = 0. See SMBus section for more information.
NVT211
Table 12. LIST OF REGISTERS
Read Address (Hex)
Write Address (Hex)
Not Applicable
Not Applicable
Address Pointer
Name
Undefined
Power-on Default
00
Not Applicable
Local Temperature Value
0000 0000 (0x00)
01
Not Applicable
External Temperature Value High Byte
0000 0000 (0x00)
02
Not Applicable
Status
Undefined
03
09
Configuration
0000 0000 (0x00)
04
0A
Conversion Rate
0000 1000 (0x08)
05
0B
Local Temperature High Limit
0101 0101 (0x55) (85°C)
06
0C
Local Temperature Low Limit
0000 0000 (0x00) (0°C)
07
0D
External Temperature High Limit High Byte
0101 0101 (0x55) (85°C)
08
0E
External Temperature Low Limit High Byte
0000 0000 (0x00) (0°C)
Not Applicable
0F (Note 1)
10
Not Applicable
One-shot
External Temperature Value Low Byte
0000 0000
11
11
External Temperature Offset High Byte
0000 0000
12
12
External Temperature Offset Low Byte
0000 0000
13
13
External Temperature High Limit Low Byte
0000 0000
14
14
External Temperature Low Limit Low Byte
0000 0000
19
19
External THERM Limit
0110 1100 (0x6C) (108°C)
20
20
Local THERM Limit
0110 1100 (0x6C) (108°C)
21
21
THERM Hysteresis
0000 1010 (0x0A) (10°C)
22
22
Consecutive ALERT
0000 0001 (0x01)
FE
Not Applicable
Manufacturer ID
0100 0001 (0x41)
1. Writing to Address 0x0F causes the NVT211 to perform a single measurement. It is not a data register, and it does not matter what data is
written to it.
Serial Bus Interface
slave peripherals connected to the serial bus
respond to the start condition and shift in the next
eight bits, consisting of a 7-bit address (MSB first)
plus an R/W bit, which determines the direction of
the data transfer, that is, whether data is written to,
or read from, the slave device. The peripheral
whose address corresponds to the transmitted
address responds by pulling the data line low
during the low period before the ninth clock pulse,
known as the acknowledge bit. All other devices
on the bus remain idle while the selected device
waits for data to be read from or written to it. If the
R/W bit is a 0, the master writes to the slave
device. If the R/W bit is a 1, the master reads from
the slave device.
2. Data is sent over the serial bus in a sequence of
nine clock pulses, eight bits of data followed by an
acknowledge bit from the slave device. Transitions
on the data line must occur during the low period
of the clock signal and remain stable during the
high period, since a low-to-high transition when
the clock is high can be interpreted as a stop
signal. The number of data bytes that can be
transmitted over the serial bus in a single read or
Control of the NVT211 is carried out via the serial bus.
The NVT211 is connected to this bus as a slave device, under
the control of a master device.
The NVT211 has an SMBus/I2C timeout feature. When
this is enabled, the SMBus/I2C times out after typically
25 ms of no activity. However, this feature is not enabled by
default. Bit 7 of the consecutive alert register
(Address = 0x22) should be set to enable it.
Addressing the Device
In general, every SMBus/I2C device has a 7-bit device
address, except for some devices that have extended 10-bit
addresses. When the master device sends a device address
over the bus, the slave device with that address responds.
The NVT211 is available with one device address, 0x4C
(1001 100b). An NVT211D is also available.
The NVT211D has an SMBus/I2C address of 0x4D
(1001 101b). This is to allow two NVT211 devices on the
same bus, or if the default address conflicts with an existing
device on the SMBus/I2C. The serial bus protocol operates
as follows:
1. The master initiates a data transfer by establishing
a start condition, defined as a high-to-low
transition on SDATA, the serial data line, while
SCLK, the serial clock line, remains high. This
indicates that an address/data stream follows. All
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NVT211
without starting a new operation. For the NVT211,
write operations contain either one or two bytes,
while read operations contain one byte.
write operation is limited only by what the master
and slave devices can handle.
3. When all data bytes have been read or written,
stop conditions are established. In write mode, the
master pulls the data line high during the tenth
clock pulse to assert a stop condition. In read
mode, the master device overrides the
acknowledge bit by pulling the data line high
during the low period before the ninth clock pulse.
This is known as no acknowledge. The master
takes the data line low during the low period
before the tenth clock pulse, then high during the
tenth clock pulse to assert a stop condition.
Any number of bytes of data are transferable over
the serial bus in one operation, but it is not
possible to mix read and write in one operation
because the type of operation is determined at the
beginning and cannot subsequently be changed
To write data to one of the device data registers, or to read
data from it, the address pointer register must be set so that
the correct data register is addressed. The first byte of a write
operation always contains a valid address that is stored in the
address pointer register. If data is to be written to the device,
the write operation contains a second data byte that is written
to the register selected by the address pointer register.
This procedure is illustrated in Figure 15. The device
address is sent over the bus followed by R/W set to 0. This
is followed by two data bytes. The first data byte is the
address of the internal data register to be written to, which
is stored in the address pointer register. The second data byte
is the data to be written to the internal data register.
1
9
9
1
SCLK
A6
SDATA
A5
START BY
MASTER
A4
A3
A2
A1
R/W
A0
D7
FRAME 1
SERIAL BUS ADDRESS BYTE
D6
D5
D4
D3
D2
D1
D0
ACK. BY
NVT211
FRAME 2
ADDRESS POINTER REGISTER BYTE
ACK. BY
NVT211
1
9
SCLK (CONTINUED)
SDATA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1
FRAME 3
DATA BYTE
D0
ACK. BY STOP BY
NVT211 MASTER
Figure 15. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
1
9
9
1
SCLK
SDATA
A6
START BY
MASTER
A5
A4
A3
A2
A1
A0
FRAME 1
SERIAL BUS ADDRESS BYTE
R/W
D7
ACK. BY
NVT211
D6
D5
D4
D3
D2
D1
D0
ACK. BY
NVT211
FRAME 2
ADDRESS POINTER REGISTER BYTE
STOP BY
MASTER
Figure 16. Writing to the Address Pointer Register Only
9
1
1
9
SCLK
SDATA
A6
START BY
MASTER
A5
A4
A3
A2
A1
A0 R/W
FRAME 1
SERIAL BUS ADDRESS BYTE
D7
ACK. BY
NVT211
D6
D5
D4
D3
D2
D0
ACK. BY
NVT211
FRAME 2
ADDRESS POINTER REGISTER BYTE
Figure 17. Reading Data from a Previously Selected Register
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D1
STOP BY
MASTER
NVT211
When reading data from a register there are two possibilities.
• If the address pointer register value of the NVT211 is
unknown or not the desired value, it is first necessary to
set it to the correct value before data can be read from
the desired data register. This is done by writing to the
NVT211 as before, but only the data byte containing
the register read address is sent, because data is not to
be written to the register see Figure 16.
A read operation is then performed consisting of the
serial bus address, R/W bit set to 1, followed by the
data byte read from the data register see Figure 17.
• If the address pointer register is known to be at the
desired address, data can be read from the
corresponding data register without first writing to the
address pointer register and the bus transaction shown
in Figure 16 can be omitted.
Notes:
• It is possible to read a data byte from a data register
without first writing to the address pointer register.
However, if the address pointer register is already at the
correct value, it is not possible to write data to a register
without writing to the address pointer register because
the first data byte of a write is always written to the
address pointer register.
• Some of the registers have different addresses for read
and write operations. The write address of a register
must be written to the address pointer if data is to be
written to that register, but it may not be possible to
read data from that address. The read address of a
register must be written to the address pointer before
data can be read from that register.
1. SMBALERT is pulled low.
2. Master initiates a read operation and sends the
alert response address (ARA = 0001 100). This is
a general call address that must not be used as a
specific device address.
3. The device whose ALERT output is low responds
to the alert response address and the master reads
its device address. As the device address is seven
bits, an LSB of 1 is added. The address of the
device is now known and it can be interrogated in
the usual way.
4. If more than one device’s ALERT output is low,
the one with the lowest device address takes
priority, in accordance with normal SMBus/I2C
arbitration.
Once the NVT211 has responded to the alert response
address, it resets its ALERT output, provided that the error
condition that caused the ALERT no longer exists. If the
SMBALERT line remains low, the master sends the ARA
again, and so on until all devices whose ALERT outputs
were low have responded.
Low Power Standby Mode
The NVT211 can be put into low power standby mode by
setting Bit 6 of the configuration register. When Bit 6 is low,
the NVT211 operates normally. When Bit 6 is high, the ADC
is inhibited, and any conversion in progress is terminated
without writing the result to the corresponding value
register. However, the SMBus/I2C is still enabled. Power
consumption in the standby mode is reduced to 5 mA if there
is no SMBus/I2C activity, or 30 mA if there are clock and
data signals on the bus.
When the device is in standby mode, it is possible to
initiate a one-shot conversion of both channels by writing to
the one-shot register (Address 0x0F), after which the device
returns to standby. It does not matter what is written to the
one-shot register, all data written to it is ignored. It is also
possible to write new values to the limit register while in
standby mode. If the values stored in the temperature value
registers are outside the new limits, an ALERT is generated,
even though the NVT211 is still in standby.
ALERT Output
This is applicable when Pin 6 is configured as an ALERT
output. The ALERT output goes low whenever an
out-of-limit measurement is detected, or if the remote
temperature sensor is open circuit. It is an open-drain output
and requires a pullup resistor to VDD. Several ALERT outputs
can be wire-OR’ed together, so that the common line goes
low if one or more of the ALERT outputs goes low.
The ALERT output can be used as an interrupt signal to a
processor, or as an SMBALERT. Slave devices on the
SMBus/I2C cannot normally signal to the bus master that
they want to talk, but the SMBALERT function allows them
to do so.
One or more ALERT outputs can be connected to a
common SMBALERT line that is connected to the master.
When the SMBALERT line is pulled low by one of the
devices, the following procedure occurs (see Figure 18):
Sensor Fault Detection
At its D+ input, the NVT211 contains internal sensor fault
detection circuitry. This circuit can detect situations where
an external remote diode is either not connected or
incorrectly connected to the NVT211. A simple voltage
comparator trips if the voltage at D+ exceeds VDD − 1.0 V
(typical), signifying an open circuit between D+ and D−.
The output of this comparator is checked when a conversion
is initiated. Bit 2 of the status register (open flag) is set if a
fault is detected. If the ALERT pin is enabled, setting this
flag causes ALERT to assert low.
If the user does not wish to use an external sensor with the
NVT211, tie the D+ and D− inputs together to prevent
continuous setting of the open flag.
MASTER RECEIVES SMBALERT
START
ALERT RESPONSE
ADDRESS
MASTER SENDS
ARA AND READ
COMMAND
RD ACK
DEVICE
ADDRESS
NO
STOP
ACK
DEVICE SENDS
ITS ADDRESS
Figure 18. Use of SMBALERT
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NVT211
The NVT211 Interrupt System
TEMPERATURE
The NVT211 has two interrupt outputs, ALERT and
THERM. Both have different functions and behavior.
ALERT is maskable and responds to violations of software
programmed temperature limits or an open-circuit fault on
the external diode. THERM is intended as a fail-safe
interrupt output that cannot be masked.
If the external or local temperature exceeds the
programmed high temperature limits, or equals or exceeds
the low temperature limits, the ALERT output is asserted
low. An open-circuit fault on the external diode also causes
ALERT to assert. ALERT is reset when serviced by a master
reading its device address, provided the error condition has
gone away and the status register has been reset.
The THERM output asserts low if the external or local
temperature exceeds the programmed THERM limits.
THERM temperature limits should normally be equal to or
greater than the high temperature limits. THERM is reset
automatically when the temperature falls back within the
THERM limit. A hysteresis value can be programmed; in
which case, THERM resets when the temperature falls to the
limit value minus the hysteresis value. This applies to both
local and remote measurement channels. The power-on
hysteresis default value is 10°C, but this can be
reprogrammed to any value after powerup.
The hysteresis loop on the THERM outputs is useful when
THERM is used, for example, as an on/off controller for a
fan. The user’s system can be set up so that when THERM
asserts, a fan is switched on to cool the system. When
THERM goes high again, the fan can be switched off.
Programming a hysteresis value protects from fan jitter,
where the temperature hovers around the THERM limit, and
the fan is constantly switched.
1005C
905C
Binary Representation
0 000 0000
1°C
0 000 0001
10°C
0 000 1010
HIGH TEMP LIMIT
605C
505C
405C
RESET BY MASTER
ALERT
1
4
THERM
2
3
Figure 19. Operation of the ALERT and THERM
Interrupts
• If the measured temperature exceeds the high
•
•
•
•
•
•
0°C
THERM LIMIT − HYSTERESIS
705C
Table 13. THERM HYSTERESIS
THERM Hysteresis
THERM LIMIT
805C
temperature limit, the ALERT output asserts low.
If the temperature continues to increase and exceeds the
THERM limit, the THERM output asserts low.
The THERM output deasserts (goes high) when the
temperature falls to THERM limit minus hysteresis. In ,
the default hysteresis value of 10°C is shown.
The ALERT output deasserts only when the
temperature has fallen below the high temperature
limit, and the master has read the device address and
cleared the status register.
Pin 6 on the NVT211 can be configured as either an
ALERT output or as an additional THERM output.
THERM2 asserts low when the temperature exceeds the
programmed local and/or remote high temperature
limits. It is reset in the same manner as THERM and is
not maskable.
The programmed hysteresis value also applies to
THERM2.
Figure 20 shows how THERM and THERM2 operate
together to implement two methods of cooling the system.
In this example, the THERM2 limits are set lower than the
THERM limits. The THERM2 output is used to turn on a
fan.
Figure 19 shows how the THERM and ALERT outputs
operate. The ALERT output can be used as a SMBALERT
to signal to the host via the SMBus/I2C that the temperature
has risen. The user can use the THERM output to turn on a
fan to cool the system, if the temperature continues to
increase. This method ensures that there is a fail-safe
mechanism to cool the system, without the need for host
intervention.
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NVT211
100 W
TEMPERATURE
905C
REMOTE
TEMPERATURE
SENSOR
THERM LIMIT
805C
705C
605C
1 nF
D−
Figure 21. Filter between Remote Sensor and NVT211
Factors Affecting Diode Accuracy
THERM2 LIMIT
505C
100 W
D+
405C
Remote Sensing Diode
305C
THERM2
1
THERM
The NVT211 is designed to work with discrete transistors.
Substrate transistors are generally PNP types with the
collector connected to the substrate. Discrete types are either
PNP or NPN transistors connected as diodes (base-shorted
to collector). If an NPN transistor is used, the collector and
base are connected to D+ and the emitter to D−. If a PNP
transistor is used, the collector and base are connected to D−
and the emitter to D+.
To reduce the error due to variations in discrete transistors,
consider several factors:
• The ideality factor, nF, of the transistor is a measure of
the deviation of the thermal diode from ideal behavior.
The NVT211 is trimmed for an nF value of 1.008. The
following equation may be used to calculate the error
introduced at a temperature, T (°C), when using a
transistor whose nF does not equal 1.008. Consult the
processor data sheet for the nF values.
4
2
3
Figure 20. Operation of the THERM and THERM2
Interrupts
• When the THERM2 limit is exceeded, the THERM2
•
•
•
signal asserts low.
If the temperature continues to increase and exceeds the
THERM limit, the THERM output asserts low.
The THERM output deasserts (goes high) when the
temperature falls to THERM limit minus hysteresis. In
Figure 20, there is no hysteresis value shown.
As the system cools further, and the temperature falls
below the THERM2 limit, the THERM2 signal resets.
Again, no hysteresis value is shown for THERM2.
DT = (nF − 1.008)/1.008 × (273.15 Kelvin + T)
Both the external and internal temperature measurements
cause THERM and THERM2 to operate as described.
To factor this in, the user writes the DT value to the offset
register. It is then automatically added to, or subtracted
from, the temperature measurement.
If a discrete transistor is used with the NVT211, the best
accuracy is obtained by choosing devices according to the
following criteria:
• Base-emitter voltage greater than 0.25 V at 6 mA, at the
highest operating temperature
• Base-emitter voltage less than 0.95 V at 100 mA, at the
lowest operating temperature
• Base resistance less than 100 W
• Small variation in hFE (50 to 150) that indicates tight
control of VBE characteristics
Application Information
Noise Filtering
For temperature sensors operating in noisy environments,
the industry standard practice was to place a capacitor across
the D+ and D− pins to help combat the effects of noise.
However, large capacitances affect the accuracy of the
temperature measurement, leading to a recommended
maximum capacitor value of 1,000 pF. Although this
capacitor reduces the noise, it does not eliminate it, making
it difficult to use the sensor in a very noisy environment.
The NVT211 has a major advantage over other devices
when it comes to eliminating the effects of noise on the
external sensor. The series resistance cancellation feature
allows a filter to be constructed between the external
temperature sensor and the part. The effect of any filter
resistance seen in series with the remote sensor is
automatically cancelled from the temperature result.
The construction of a filter allows the NVT211 and the
remote temperature sensor to operate in noisy environments.
Figure 21 shows a low-pass R-C-R filter, where R = 100 W
and C = 1 nF. This filtering reduces both common-mode and
differential noise.
Transistors, such as the 2N3904, 2N3906, or equivalents
in SOT−23 packages are suitable devices to use.
Thermal Inertia and Self-heating
Accuracy depends on the temperature of the remote
sensing diode and/or the internal temperature sensor being
at the same temperature as that being measured. Many
factors can affect this. Ideally, place the sensor in good
thermal contact with the part of the system being measured.
If it is not, the thermal inertia caused by the sensor’s mass
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NVT211
• Try to minimize the number of copper/solder joints that
causes a lag in the response of the sensor to a temperature
change. In the case of the remote sensor, this should not be
a problem since it is either a substrate transistor in the
processor or a small package device, such as the SOT−23,
placed in close proximity to it.
The on-chip sensor, however, is often remote from the
processor and only monitors the general ambient
temperature around the package. How accurately the
temperature of the board and/or the forced airflow reflects
the temperature to be measured dictates the accuracy of the
measurement. Self-heating due to the power dissipated in
the NVT211 or the remote sensor causes the chip
temperature of the device or remote sensor to rise above
ambient. However, the current forced through the remote
sensor is so small that self-heating is negligible. In the case
of the NVT211, the worst-case condition occurs when the
device is converting at 64 conversions per second while
sinking the maximum current of 1 mA at the ALERT and
THERM output. In this case, the total power dissipation in
the device is about 4.5 mW. The thermal resistance, qJA, of
the 8-lead DFN is approximately 142°C/W.
•
•
•
Layout Considerations
Digital boards can be electrically noisy environments, and
the NVT211 is measuring very small voltages from the
remote sensor, so care must be taken to minimize noise
induced at the sensor inputs. Take the following precautions:
• Place the NVT211 as close as possible to the remote
sensing diode. Provided that the worst noise sources,
that is, clock generators and data/address buses are
avoided, this distance can be 4 inches to 8 inches.
• Route the D+ and D– tracks close together, in parallel,
with grounded guard tracks on each side. To minimize
inductance and reduce noise pickup, a 5 mil track width
and spacing is recommended. Provide a ground plane
under the tracks, if possible.
GND
can cause thermocouple effects. Where copper/solder
joints are used, make sure that they are in both the D+
and D− path and at the same temperature.
Thermocouple effects should not be a major problem as
1°C corresponds to about 200 mV, and thermocouple
voltages are about 3 mV/°C of temperature difference.
Unless there are two thermocouples with a big
temperature differential between them, thermocouple
voltages should be much less than 200 mV.
Place a 0.1 mF bypass capacitor close to the VDD pin. In
extremely noisy environments, place an input filter
capacitor across D+ and D− close to the NVT211. This
capacitance can effect the temperature measurement, so
ensure that any capacitance seen at D+ and D− is, at
maximum, 1,000 pF. This maximum value includes the
filter capacitance, plus any cable or stray capacitance
between the pins and the sensor diode.
If the distance to the remote sensor is more than
8 inches, the use of twisted pair cable is recommended.
A total of 6 feet to 12 feet is needed.
For really long distances (up to 100 feet), use a shielded
twisted pair, such as the Belden No. 8451 microphone
cable. Connect the twisted pair to D+ and D− and the
shield to GND close to the NVT211. Leave the remote
end of the shield unconnected to avoid ground loops.
Because the measurement technique uses switched
current sources, excessive cable or filter capacitance can
affect the measurement. When using long cables, the filter
capacitance can be reduced or removed.
Application Circuit
Figure 23 shows a typical application circuit for the
NVT211, using a discrete sensor transistor connected via a
shielded, twisted pair cable. The pullups on SCLK, SDATA,
and ALERT are required only if they are not provided
elsewhere in the system.
5 MIL
5 MIL
D+
5 MIL
5 MIL
D−
5 MIL
5 MIL
GND
5 MIL
Figure 22. Typical Arrangement of Signal Tracks
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NVT211
VDD
VDD
0.1 mF
VDD
SCLK
D+
D−
2N3906
TYP 10 kW
NVT211
SHIELD
SMBus/I2C
CONTROLLER
SDATA
ALERT/
THERM2
VDD
THERM
TYP 10 kW
GND
OVERTEMPERATURE
SHUTDOWN
Figure 23. Typical Application Circuit
Table 14. ORDERING INFORMATION
Device Order Number*
Package
Description
Package
Option
Marking
SMBus
Address
THERM
Limit
Shipping†
NVT211CMTR2G
8-lead WDFN
MT
NC
0x4C
108°C
3,000 Tape & Reel
NVT211DMTR2G
8-lead WDFN
MT
ND
0x4D
108°C
3,000 Tape & Reel
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
*The “G’’ suffix indicates Pb-Free package available.
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NVT211
PACKAGE DIMENSIONS
WDFN8 2x2, 0.5P
CASE 511AT
ISSUE O
D
L
L
A
B
NOTES:
1. DIMENSIONING AND TOLERANCING PER
ASME Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. DIMENSION b APPLIES TO PLATED
TERMINAL AND IS MEASURED BETWEEN
0.15 AND 0.30 MM FROM TERMINAL TIP.
L1
PIN ONE
REFERENCE
2X
ÍÍÍ
ÍÍÍ
DETAIL A
E
ALTERNATE TERMINAL
CONSTRUCTIONS
0.10 C
2X
0.10 C
ÉÉÉ
ÉÉÉ
TOP VIEW
EXPOSED Cu
DETAIL B
0.05 C
0.05 C
A1
A3
SIDE VIEW
e/2
MOLD CMPD
DETAIL B
A
8X
ALTERNATE
CONSTRUCTIONS
C
1
7X
4
MILLIMETERS
MIN
MAX
0.70
0.80
0.00
0.05
0.20 REF
0.20
0.30
2.00 BSC
2.00 BSC
0.50 BSC
0.40
0.60
--0.15
0.50
0.70
RECOMMENDED
SOLDERING FOOTPRINT*
SEATING
PLANE
7X
DETAIL A
e
DIM
A
A1
A3
b
D
E
e
L
L1
L2
PACKAGE
OUTLINE
0.78
L
L2
2.30
0.88
8
5
BOTTOM VIEW
8X
b
0.10 C A
0.05 C
1
8X
B
0.30
NOTE 3
0.50
PITCH
DIMENSIONS: MILLIMETERS
*For additional information on our Pb-Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
ON Semiconductor is licensed by Philips Corporation to carry the I2C Bus Protocol.
ON Semiconductor and
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC owns the rights to a number of patents, trademarks,
copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. SCILLC
reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any
particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without
limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications
and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC
does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for
surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where
personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and
its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly,
any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture
of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
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For additional information, please contact your local
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NVT211/D