EVAL-ADT7463EB ON Semiconductor, EVAL-ADT7463EB Datasheet - Page 17

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

Specifications of EVAL-ADT7463EB

• Lead Free Status / RoHS Status: Supplier Unconfirmed

If a discrete transistor is used, the collector will not be grounded
and should be 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. Figures 15a and 15b
show how to connect the ADT7463 to an NPN or PNP transis-
tor 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.
To measure ∆V
of I and N
65 kHz low-pass filter to remove noise and to a chopper-stabilized
amplifier that performs the functions of amplification and recti-
fication of the waveform to produce a dc voltage proportional to
∆V
ture output in 10-bit, twos complement format. To further reduce
the effects of noise, digital filtering is performed by averaging
the results of 16 measurement cycles. A remote temperature
measurement takes nominally 25.5 ms. The results of remote
temperature measurements are stored in 10-bit, twos complement
format, as illustrated in Table III. The extra resolution for the
temperature measurements is held in the Extended Resolution
Register 2 (Reg. 0x77). This gives temperature readings with a
resolution of 0.25 C.
REV. C
BE
. This voltage is measured by the ADC to give a tempera-
Temperature
–128 C
–125 C
–100 C
–75 C
–50 C
–25 C
–10 C
0 C
+10.25 C
+25.5 C
+50.75 C
+75 C
+100 C
+125 C
+127 C
*Bold denotes 2 LSBs of measurement in Extended
Resolution Register 2 (Reg. 0x77) with 0.25 C resolution.
Table III. Temperature Data Format
I. The resulting waveform is passed through a
BE
, the sensor is switched between operating currents
Digital Output (10-Bit)*
1000 0000 00
1000 0011 00
1001 1100 00
1011 0101 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
–17–
Nulling Out Temperature Errors
As CPUs run faster, it is getting more difficult to avoid high
frequency clocks when routing the D+, D– traces around a
system board. Even when recommended layout guidelines are
followed, there may still be temperature errors attributed to
noise being coupled onto the D+/D– lines. High frequency noise
generally has the effect of giving temperature measurements that are
too high by a constant amount. The ADT7463 has temperature
offset registers at Addresses 0x70, 0x72 for the Remote 1 and
Remote 2 temperature channels. By doing a one-time calibration
of the system, one can determine the offset caused by system
board noise and null it out using the offset registers. The offset
registers automatically add a twos complement 8-bit reading to
every temperature measurement. The LSBs add 0.25°C offset to
the temperature reading so the 8-bit register effectively allows
temperature offsets of up to 32 C with a resolution of 0.25 C.
This ensures that the readings in the temperature measurement
registers are as accurate as possible.
Temperature Offset Registers
Reg. 0x70 Remote 1 Temperature Offset = 0x00 (0°C Default)
Reg. 0x71 Local Temperature Offset = 0x00 (0°C Default)
Reg. 0x72 Remote 2 Temperature Offset = 0x00 (0°C Default)
Figure 15a. Measuring Temperature Using an
NPN Transistor
Figure 15b. Measuring Temperature Using a PNP
Transistor
2N3904
2N3906
NPN
PNP
D+
D–
D+
D–
ADT7463
ADT7463
ADT7463