EVAL-ADT7463EB ON Semiconductor, EVAL-ADT7463EB Datasheet - Page 16

• Manufacturer Part Number: EVAL-ADT7463EB
• Manufacturer: ON Semiconductor

Specifications of EVAL-ADT7463EB

• Lead Free Status / RoHS Status: Supplier Unconfirmed

ADT7463
TEMPERATURE MEASUREMENT SYSTEM
Local Temperature Measurement
The ADT7463 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 temperature register
(Address 26h). As both positive and negative temperatures 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 C to +127 C
with a resolution of 0.25 C. However, this exceeds the operating
temperature range of the device, so local temperature measure-
ments outside this range are not possible.
Remote Temperature Measurement
The ADT7463 can measure the temperature of two remote diode
sensors or diode-connected transistors connected to Pins 15 and
16, or 17 and 18.
The forward voltage of a diode or diode-connected transistor
operated at a constant current exhibits a negative temperature
coefficient of about –2 mV/ C. Unfortunately, the absolute
TRANSISTOR
SENSING
REMOTE
CPU
Figure 14. Signal Conditioning for Remote Diode Temperature Sensors
THERMDA
THERMDC
D+
D–
I
N
DIODE
BIAS
I
I
BIAS
–16–
LOW-PASS
f
C
FILTER
= 65kHz
value of V
tion is required to null this out, so the technique is unsuitable
for mass production. The technique used in the ADT7463 is to
measure the change in V
different currents.
This is given by
where:
K is Boltzmann’s constant.
q is the charge on the carrier.
T is the absolute temperature in Kelvins.
N is the ratio of the two currents.
Figure 14 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.
V
DD
BE
varies from device to device and individual calibra-
∆V
BE
BE
=
when the device is operated at two
KT q
× ln( )
V
V
OUT+
OUT–
N
TO ADC
REV. C