EVAL-ADT7475EB ON Semiconductor, EVAL-ADT7475EB Datasheet - Page 14

• Manufacturer Part Number: EVAL-ADT7475EB
• Description: BOARD EVALUATION FOR ADT7475
• Manufacturer: ON Semiconductor
• Series: dBCool®r
• Type: Temperature Sensorr

Specifications of EVAL-ADT7475EB

• Contents: Evaluation Board
• For Use With/related Products: ADT7475
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

because differential inputs, by their very nature, have a high
immunity to noise.
Factors Affecting Diode Accuracy
Remote Sensing Diode
transistors built into processors or with discrete transistors.
Substrate transistors are generally PNP types with the
collector connected to the substrate. Discrete types can be
either PNP or NPN transistors connected as a diode
(base−shorted to the collector). If an NPN transistor is used,
the collector and base are connected to D+ and the emitter
to D−. If a PNP transistor is used, the collector and base are
connected to D− and the emitter is connected to D+.
discrete transistors, a number of factors should be taken into
consideration:
•
•
The ADT7475 is designed to work with either substrate
To reduce the error due to variations in both substrate and
The ideality factor, n
the deviation of the thermal diode from ideal behavior.
The ADT7475 is trimmed for an n
the following equation to calculate the error introduced
at a temperature, T (°C), when using a transistor whose
n
the n
Some CPU manufacturers specify the high and low
current levels of the substrate transistors. The high
current level of the ADT7475, I
low level current, I
current levels do not match the current levels specified
by the CPU manufacturer, it might be necessary to
remove an offset. The CPU’s data sheet advises
whether this offset needs to be removed and how to
To factor this in, the user can write the DT value to the
offset register. The ADT7475 automatically adds it
to or subtracts it from the temperature measurement.
f
does not equal 1.008. See the processor data sheet for
Figure 21. Measuring Temperature Using an
Figure 22. Measuring Temperature Using a
f
DT + n
values.
2N3904
2N3906
f
NPN
PNP
* 1.008
NPN Transistor
PNP Transistor
LOW
f
, of the transistor is a measure of
, is 11 mA. If the ADT7475
273.15 k ) T
D+
D–
D+
D–
ADT7475
ADT7475
HIGH
f
value of 1.008. Use
, is 180 mA and the
(eq. 2)
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14
accuracy is obtained by choosing devices according to the
following criteria:
•
•
•
•
SOT−23 packages, are suitable devices to use.
Table 3. Twos Complement Temperature Data Format
1. Bold numbers denote 2 LSBs of measurement in the Extended
Table 4. Extended Range, Temperature Data Format
1. Bold numbers denote 2 LSBs of measurement in the Extended
If a discrete transistor is used with the ADT7475, the best
Transistors, such as 2N3904, 2N3906, or equivalents in
calculate it. This offset can be programmed to the offset
register. If more than one offset must be considered, the
algebraic sum of these offsets must be programmed to
the offset register.
Base−emitter voltage greater than 0.25 V at 11 mA, at
the highest operating temperature.
Base−emitter voltage less than 0.95 V at 180 mA, at the
lowest operating temperature.
Base resistance less than 100 W.
Small variation in h
indicates tight control of V
Resolution Register 2 (0x77) with 0.25°C resolution.
Resolution Register 2 (0x77) with 0.25°C resolution.
Temperature
Temperature
10.25°C
50.75°C
–128°C
25.5°C
–63°C
–50°C
–25°C
–10°C
100°C
125°C
127°C
–64°C
–63°C
100°C
125°C
191°C
75°C
–1°C
10°C
25°C
50°C
75°C
0°C
0°C
1°C
FE
Digital Output (10−Bit) (Note 1)
Digital Output (10−Bit) (Note 1)
1000 0000 00 (diode fault)
1100 0001 00
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
0000 0000 00 (diode fault)
0000 0001 00
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
(approximately 50 to 150) that
BE
characteristics.