ADM1027ARQZ-RL71 ONSEMI [ON Semiconductor], ADM1027ARQZ-RL71 Datasheet - Page 14

• Manufacturer Part Number: ADM1027ARQZ-RL71
• Manufacturer: ONSEMI [ON Semiconductor]

ADM1027
TEMPERATURE MEASUREMENT SYSTEM
Local Temperature Measurement
The ADM1027 contains an on-chip band gap temperature
sensor whose output is digitized by the on-chip 10-bit ADC.
The 8-bit MSB temperature data is stored in the local temp
register (Address 0x26). As both positive and negative tempera-
tures can be measured, the temperature data is stored in twos
complement format, as shown in Table III. Theoretically, the
temperature sensor and ADC can measure temperatures from
–128
exceeds the operating temperature range of the device (0
105
are not possible. Temperature measurement from –127
+127
Remote Temperature Measurement
The ADM1027 can measure the temperature of two remote
diode sensors or diode-connected transistors connected to
Pins 15 and 16, or 17 and 18.
o
C), so local temperature measurements outside this range
o
o
C to +127
C is possible using a remote sensor.
o
TRANSISTOR
C with a resolution of 0.25
SENSING
REMOTE
CPU
Figure 13. Signal Conditioning for Remote Diode Temperature Sensors
THERMDA
THERMDC
D+
D–
o
C. However, this
I
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N
DIODE
o
BIAS
C to
o
I
C to
I
BIAS
–14–
LOW-PASS
f
C
FILTER
= 65kHz
The forward voltage of a diode or diode-connected transistor,
operated at a constant current, exhibits a negative temperature
coefficient of about –2 mV/
value of V
tion is required to null this out, so the technique is unsuitable
for mass production. The technique used in the ADM1027 is to
measure the change in V
different currents. This is given by
where:
K is Boltzmann’s constant.
q is charge on the carrier.
T is absolute temperature in kelvins.
N is the ratio of the two currents.
Figure 13 shows the input signal conditioning used to measure
the output of a remote temperature sensor. This figure shows the
external sensor as a substrate transistor, provided for temperature
monitoring on some microprocessors. It could equally well be a
discrete transistor such as a 2N3904/06.
V
DD
be
varies from device to device, and individual calibra-
DV
be
be
=
when the device is operated at two
KT q
o
C. Unfortunately, the absolute
¥
V
V
ln
OUT+
OUT–
( )
N
TO ADC
REV. A