ADT7467 Analog Devices, Inc., ADT7467 Datasheet - Page 16

• Manufacturer Part Number: ADT7467
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

ADT7467
Table 6. 10-Bit A/D Output Code vs. V
V
<0.0065
0.0065–0.0130
0.0130–0.0195
0.0195–0.0260
0.0260–0.0325
0.0325–0.0390
0.0390–0.0455
0.0455–0.0521
0.0521–0.0586
1.6675–1.6740
3.330–3.3415
5.0025–5.0090
6.5983–6.6048
6.6048–6.6113
6.6113–6.6178
6.6178–6.6244
6.6244–6.6309
6.6309–6.6374
6.6374–6.4390
6.6439–6.6504
6.6504–6.6569
6.6569–6.6634
>6.6634
TEMPERATURE MEASUREMENT
A simple method of measuring temperature is to exploit the
negative temperature coefficient of a diode, measuring the base-
emitter voltage (V
current. Unfortunately, this technique requires calibration to
null the effect of the absolute value of V
each device.
The technique used in the ADT7467 is to measure the change
in V
devices have used only two operating currents, but the use of a
third current allows automatic cancellation of resistances in
series with the external temperature sensor.
Figure 24 shows the input signal conditioning used to measure
the output of an external temperature sensor. This figure shows
the external sensor as a substrate transistor, but it could equally
be a discrete transistor. If a discrete transistor is used, the
collector is not grounded and should be linked to the base. To
prevent ground noise from interfering with the measurement,
CC
(5 V
BE
when the device is operated at three currents. Previous
IN
)
BE
) of a transistor operated at constant
V
<0.0042
0.0042–0.0085
0.0085–0.0128
0.0128–0.0171
0.0171–0.0214
0.0214–0.0257
0.0257–0.0300
0.0300–0.0343
0.0343–0.0386
1.100–1.1042
2.200–2.2042
3.300–3.3042
4.3527–4.3570
4.3570–4.3613
4.3613–4.3656
4.3656–4.3699
4.3699–4.3742
4.3742–4.3785
4.3785–4.3828
4.3828–4.3871
4.3871–4.3914
4.3914–4.3957
>4.3957
CC
(3.3 V
Input Voltage
IN
)
BE
IN
, which varies from
V
<0.00293
0.0293–0.0058
0.0058–0.0087
0.0087–0.0117
0.0117–0.0146
0.0146–0.0175
0.0175–0.0205
0.0205–0.0234
0.0234–0.0263
0.7500–0.7529
1.5000–1.5029
2.2500–2.2529
2.9677–2.9707
2.9707–2.9736
2.9736–2.9765
2.9765–2.9794
2.9794–2.9824
2.9824–2.9853
2.9853–2.9882
2.9882–2.9912
2.9912–2.9941
2.9941–2.9970
>2.9970
CCP
Rev. A | Page 16 of 80
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. C1 can optionally be added as a noise filter (the
recommended maximum value is 1,000 pF). However, a better
option in noisy environments is to add a filter as described in
the Noise Filtering section.
Local Temperature Measurement
The ADT7467 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 tempera-
ture register (Address 0x26). Because both positive and negative
temperatures can be measured, the temperature data is stored in
Offset 64 format or twos complement format, as shown in
Table 7 and Table 8. Theoretically, the temperature sensor and
ADC can measure temperatures from −128°C to +127°C (or
−61°C to +191°C in the extended temperature range) with a
resolution of 0.25°C. However, this exceeds the operating
temperature range of the device, preventing local temperature
measurements outside the ADT7467 operating temperature range.
1
2
3
4
5
6
7
8
256 (1/4 scale)
512 (1/2 scale)
768 (3/4 scale)
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
Decimal
0
•
•
•
•
•
•
•
•
•
•
•
•
1023
A/D Output
Binary (10 Bits)
00000000 01
00000000 10
00000000 11
00000001 00
00000001 01
00000001 10
00000001 11
00000010 00
11111101 01
11111101 10
11111101 11
11111110 00
11111110 01
11111110 10
11111110 11
11111111 00
11111111 01
11111111 10
00000000 00
01000000 00
10000000 00
11000000 00
11111111 11