ADT7476ARQH ONSEMI [ON Semiconductor], ADT7476ARQH Datasheet - Page 17

• Manufacturer Part Number: ADT7476ARQH
• Description: dBCOOL Remote Thermal Controller and Voltage Monitor
• Manufacturer: ONSEMI [ON Semiconductor]

Remote Temperature Measurement
The ADT7476 can measure the temperature of two remote
diode sensors or diode−connected transistors connected to
Pin 17 and Pin 18, or Pin 15 and Pin 16.
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 value of V
individual calibration is required to null this out. As a result,
this technique is unsuitable for mass production. The
technique used in the ADT7476 is to measure the change in
V
and is linked to the base. If a PNP transistor is used, the base
is connected to the D– input and the emitter to the D+ input. If
an NPN transistor is used, the emitter is connected to the D–
input and the base to the D+ input. Figure 26 and Figure 27
show how to connect the ADT7476 to an NPN or PNP
transistor for temperature measurement. To prevent ground
noise from 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.
Table 6. Twos Complement Temperature Data Format
1. Bold numbers denote 2 LSB of measurement in the Extended
BE
If a discrete transistor is used, the collector is not grounded
Resolution Register 2 (0x77) with 0.25°C resolution.
Temperature
when the device is operated at two different currents.
+10.25°C
+50.75°C
+25.5°C
–128°C
+100°C
+125°C
+127°C
–50°C
–25°C
–10°C
+75°C
0°C
TRANSISTOR
BE
Digital Output (10−Bit) (Note 1)
SENSING
1000 0000 00 (diode fault)
1100 1110 00
1110 0111 00
1111 0110 00
0000 0000 00
0000 1010 01
0001 1001 10
0011 0010 11
0100 1011 00
0110 0100 00
0111 1101 00
0111 1111 00
REMOTE
Figure 25. Signal Conditioning for Remote Diode Temperture Senors
CPU
varies from device to device, and
THERMDA
THERMDC
D+
D–
I
DIODE
BIAS
http://onsemi.com
N
×
I
I
BIAS
LOW−PASS FILTER
17
f
V
C
DD
= 65kHz
This is given by:
measure the output of a remote temperature sensor. This figure
shows the external sensor as a substrate transistor, which is
provided on some microprocessors for temperature monitoring.
It could also be a discrete transistor such as a 2N3904/2N3906.
Table 7. Extended Range, Temperature Data Format
1. Bold numbers denote 2 LSB of measurement in the Extended
Figure 25 shows the input signal conditioning used to
Resolution Register 2 (0x77) with 0.25°C resolution.
where:
Temperature
Figure 26. Measuring Temperature Using an
–64°C
100°C
125°C
191°C
–1°C
10°C
25°C
50°C
75°C
0°C
1°C
k is the Boltzmann’s constant.
q is the charge on the carrier.
T is the absolute temperature in Kelvin.
N is the ratio of the two currents.
2N3904
NPN
DV
BE
NPN Transistor
Digital Output (10−Bit) (Note 1)
0000 0000 00 (diode fault)
0011 1111 00
0100 0000 00
0100 0001 00
0100 1010 00
0101 1001 00
0111 0010 00
1000 1001 00
1010 0100 00
1011 1101 00
1111 1111 00
+ KT q
V
V
OUT+
OUT–
TO ADC
In ( N )
D+
D–
ADT7476
(eq. 1)