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PDF NCT203 Data sheet ( Hoja de datos )
| Número de pieza | NCT203 | |
| Descripción | Low Voltage High Accuracy Temperature Monitor | |
| Fabricantes | ON Semiconductor | |
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NCT203
Low Voltage, High
Accuracy Temperature
Monitor with I2C Interface
The NCT203 is a digital thermometer and undertemperature/
overtemperature alarm, intended for use in thermal management
systems requiring low power and size. The NCT203 operates over a
supply range of 1.4 V to 2.75 V making it possible to use it in a wide
range of applications including low power devices.
The NCT203 can measure the ambient temperature accurate to
±1.75°C. The device operates over a wide temperature range of −40 to
+125°C.
The NCT203 has a configurable ALERT output and over−
temperature shutdown THERM pin.
Communication with the NCT203 is accomplished via the I2C
interface which is compatible with industry standard protocols.
Through this interface the NCT203s internal registers may be
accessed. These registers allow the user to read the current
temperature, change the configuration settings and adjust limits.
An ALERT output signals when the on−chip temperature is out of
range. The THERM output is a comparator output that can be used to
shut down the system if it exceeds the programmed limit. The ALERT
output can be reconfigured as a second THERM output, if required.
Features
• Small DFN Package
• On−Chip Temperature Sensor
• Low Voltage Operation: 1.4 V to 2.75 V
• Low Quiescent Current:
♦ 44 mA Normal Mode (max)
♦ 20 mA Shutdown (max)
• Power Saving Shutdown Mode
• Operating Temperature Range of −40°C to 125°C
• 2−wire I2C Serial Interface
• Programmable Over/Undertemperature Limits
• This is a Pb−Free Device
Applications
• Smart Phones, Tablet PCs, Satellite Navigation, Smart Batteries
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DFN8
MT SUFFIX
CASE 511BU
PIN ASSIGNMENTS
VDD
NC
NC
THERM
18
27
36
45
DFN
(Top View)
SCL
SDA
ALERT/THERM2
GND
MARKING DIAGRAM
1
J2 MG
G
J2 = Specific Device Code
M = Date Code
G = Pb−Free Device
(*Note: Microdot may be in either location)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 13 of this data sheet.
© Semiconductor Components Industries, LLC, 2013
June, 2013 − Rev. 2
1
Publication Order Number:
NCT203/D
1 page  
NCT203
Theory of Operation
The NCT203 is an on−chip temperature sensor and
over/under temperature alarm. When the NCT203 is
operating normally, the on−board ADC operates in a free
running mode. The ADC digitizes the signals from the
temperature sensor and the results are stored in the
temperature value register.
The measurement results are compared with the
corresponding high, low, and THERM temperature limits,
stored in the 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.
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 I2C. The contents of
any register are also read back via the 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.
Temperature Measurement Method
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 NCT203 measures the change
in VBE when the device operates at different currents.
To measure DVBE, the operating current through the
sensor is switched among related currents. N1 x I and N2 x I
are different multiples of the current, I. The currents through
the temperature diode are switched between I and N1 x I,
giving DVBE1; and then between I and N2 x I, giving DVBE2.
The temperature is then calculated using the two DVBE
measurements.
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.
Temperature Measurement Results
The results of the temperature measurement are stored in
the temperature value register and compared with limits
programmed into the high and low limit registers.
The temperature value is in Register 0x00 and has a
resolution of 1°C.
Temperature Measurement Range
The temperature measurement range is, by default, 0°C to
+127°C. However, the NCT203 can be operated using an
extended temperature range. The extended measurement
range is −64°C to +191°C. Therefore, the NCT203 can be
used to measure the full temperature range of the NCT203,
from −40°C to +125°C.
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 NCT203 is limited
by the device temperature range of −40°C to +125°C. The
temperature register can have values from −64°C to +191°C.
It should be noted that although temperature
measurements can be made while the part is in extended
temperature mode, the NCT203 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 +125°C.
Temperature Data Format
The NCT203 has two temperature data formats. When the
temperature measurement range is from 0°C to 127°C
(default), the temperature data format for temperature
results is binary. When the measurement range is in
extended mode, an offset binary data format is used.
Temperature values are offset by 64°C in the offset binary
data format. Examples of temperatures in both data formats
are shown in Table 5.
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5
5 Page 
NCT203
priority, in accordance with normal bus arbitration.
Once the NCT203 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 NCT203 can be put into low power standby mode by
setting Bit 6 of the configuration register. When Bit 6 is low,
the NCT203 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 I2C is still enabled. Power
consumption in the standby mode is reduced to 15 mA if
there is no bus activity.
When the device is in standby mode, it is possible to
initiate a one−shot conversion 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 value stored in the temperature value register is outside
the new limits, an ALERT is generated, even though the
NCT203 is still in standby.
The NCT203 Interrupt System
The NCT203 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. THERM is intended as a
fail−safe interrupt output that cannot be masked.
If the temperature exceeds the programmed high
temperature limits, or equals or exceeds the low temperature
limits, the ALERT output is asserted low. 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 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. 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.
Table 11. THERM HYSTERESIS
THERM Hysteresis
Binary Representation
0°C 0 000 0000
1°C 0 000 0001
10°C
0 000 1010
Figure 8 shows how the THERM and ALERT outputs
operate. The ALERT output can be used as a SMBALERT
to signal to the host via the 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.
TEMPERATURE
1005C
905C
805C
705C
605C
505C
405C
ALERT
THERM
1
2
THERM LIMIT
THERM LIMIT − HYSTERESIS
HIGH TEMP LIMIT
RESET BY MASTER
4
3
Figure 8. Operation of the ALERT and THERM
Interrupts
• If the measured temperature exceeds the high
temperature limit, the ALERT output asserts low.
• If the temperature continues to increase and exceeds the
THERM limit, the THERM output asserts low. This can
be used to throttle the CPU clock or switch on a fan.
• The THERM output deasserts (goes high) when the
temperature falls to THERM limit minus hysteresis.
The default hysteresis value is 10°C.
• 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 NCT203 can be configured as either an
ALERT output or as an additional THERM output.
• THERM2 asserts low when the temperature exceeds the
programmed 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 9 shows how THERM and THERM2 operate
together to implement two methods of cooling the system.
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| PDF Descargar | [ Datasheet NCT203.PDF ] | |
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