NCT218
Low Voltage, High
Accuracy Temperature
Monitor with I
2
C Interface
The NCT218 is a dual−channel digital thermometer and
undertemperature/overtemperature alarm, intended for use in thermal
management systems requiring low power and size. The NCT218
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 NCT218 can measure the temperature of a remote thermal diode
accurate to
±1°C
and the ambient temperature accurate to
±1.75°C.
The device operates over a wide temperature range of −40°C to
+125°C.
The NCT218 includes series resistance cancellation, where up to
500
W
(typical) of resistance in series with the temperature monitoring
diode can be automatically cancelled from the temperature result,
allowing noise filtering. The NCT218 has a configurable ALERT
output and overtemperature shutdown THERM pin.
Communication with the NCT218 is accomplished via the I
2
C
interface which is compatible with industry standard protocols.
Through this interface the NCT218s internal registers may be
accessed. These registers allow the user to read the current
temperature from both the local (ambient) and remote channels,
change the configuration settings and adjust each channels limits.
An ALERT output signals when the on−chip or remote temperatures
are 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
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MARKING
DIAGRAMS
DFN8
MT SUFFIX
CASE 511BU
1
T2 MG
G
WLCSP8
CASE 567DH
M
AY
WW
G
= Date Code
= Assembly year
= Work Week
= Pb−Free Device
NCT218
AYWW
(Note: Microdot may be in either location)
PIN ASSIGNMENTS
V
DD
D+
D−
THERM
1
2
3
4
8
7
6
5
SCL
SDA
ALERT/THERM2
GND
•
•
•
•
•
•
•
•
•
•
•
DFN8
(Top View)
SCL
Small DFN Package
On−Chip and Remote 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
Series Resistance Cancellation up to 500
W
Low D− bias for Operation with Low Voltage Processors
2−wire I
2
C Serial Interface
Programmable Over/Undertemperature Limits
These are Pb−Free Devices
SDA
GND
ALERT/
THERM2
C1
B1
A1
V
DD
D+
D−
C2
A2
C3
B3
A3
Applications
•
Smart Phones, Tablet PCs, Satellite Navigation, Smart Batteries
WLCSP8
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information on page 16 of
this data sheet.
©
Semiconductor Components Industries, LLC, 2013
1
December, 2013 − Rev. 2
THERM2
Publication Order Number:
NCT218/D
NCT218
Table 2. ABSOLUTE MAXIMUM RATINGS
(Note 1)
Rating
Supply Voltage (V
DD
) to GND
D+
D− to GND
SCL, SDA, ALERT, THERM
Input current on D−
Input current on SDA, THERM
Maximum Junction Temperature
Operating Temperature Range
Storage Temperature Range
ESD Capability, Human Body Model (Note 2)
ESD Capability, Machine Model (Note 2)
I
IN
T
J(max)
TOP
T
STG
ESD
HBM
ESD
MM
Symbol
V
DD
Value
−0.3, +3
−0.3 to V
DD
+ 0.25
−0.3 to +0.6
−0.3 to +5.25
±1
−1, +50
150.7
−40 to 125
−65 to 160
2000
100
Unit
V
V
V
V
mA
mA
°C
°C
°C
V
V
Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality
should not be assumed, damage may occur and reliability may be affected.
1. Refer to ELECTRICAL CHARACTERISTICS and APPLICATION INFORMATION for Safe Operating Area.
2. This device series incorporates ESD protection and is tested by the following methods:
ESD Human Body Model tested per AEC−Q100-002 (EIA/JESD22-A114)
ESD Machine Model tested per AEC-Q100-003 (EIA/JESD22-A115)
Table 3. I
2
C TIMING − 400 kHz
Parameter
(Note 3)
Clock Frequency
Clock Period
SCL High Time
SCL Low Time
Start Setup Time
Start Hold Time (Note 4)
Data Setup Time (Note 5)
Data Hold Time (Note 6)
SCL, SDA Rise Time
SCL, SDA Fall Time
Stop Setup Time
Bus Free Time
Glitch Immunity
3.
4.
5.
6.
Symbol
f
SCLK
t
SCLK
t
HIGH
t
LOW
t
SU;STA
t
HD;STA
t
SU;DAT
t
HD;DAT
t
r
t
f
t
SU;STO
t
BUF
t
SW
0.6
1.3
50
Min
10
2.5
0.6
1.3
0.6
0.6
100
0.9
300
300
Typ
Max
400
Unit
kHz
ms
ms
ms
ms
ms
ns
ms
ns
ns
ms
ms
ns
Guaranteed by design, but not production tested.
Time from 10% of SDA to 90% of SCL.
Time for 10% or 90% of SDA to 10% of SCL.
A device must internally provide a hold time of at least 300 ns for the SDA signal to bridge the undefined region of the falling edge of SCL.
t
LOW
SCLK
t
HD;STA
t
HD;DAT
SDATA
t
BUF
STOP START
START
STOP
t
HIGH
t
SU;DAT
t
SU;STA
t
SU;STO
t
R
t
F
t
HD;STA
Figure 3. I
2
C Timing Diagram
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NCT218
Theory of Operation
Temperature Measurement Method
The NCT218 is a local and remote temperature sensor and
over/under temperature alarm, with the added ability to
automatically cancel the effect of 500
W
(typical) of
resistance in series with the temperature monitoring diode.
When the NCT218 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 I
2
C. The contents of
any register are also read back via the I
2
C. 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.
Series Resistance Cancellation
Parasitic resistance to the D+ and D− inputs to the
NCT218, 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 ofset
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 NCT218 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 NCT218 is designed to automatically
cancel typically up to 150
W
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.
A simple method of measuring temperature is to exploit
the negative temperature coefficient of a diode, measuring
the base emitter voltage (V
BE
) of a transistor operated at
constant current. However, this technique requires
calibration to null the effect of the absolute value of V
BE
,
which varies from device to device.
The technique used in the NCT218 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 4 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 resistor at
the D− input. C1 may be added as a noise filter (a
recommended maximum value of 1000 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
DV
BE
, the operating current through the
sensor is switched among three related currents. As shown
in Figure 4, 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
DV
BE1
; and then
between I and N2 x I, giving
DV
BE2
. The temperature is then
calculated using the two
DV
BE
measurements. This method
also cancels the effect of any series resistance on the
temperature measurement.
The resulting
DV
BE
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
DV
BE
.
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.
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