adm1027 Analog Devices, Inc., adm1027 Datasheet - Page 15

• Manufacturer Part Number: adm1027
• Description: Dbcool? Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

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. Figure 14 shows
how to connect the ADM1027 to an NPN or PNP transistor for
temperature measurement. To prevent ground noise from inter-
fering 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 DV
rents 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
DV
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 measure-
ment 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
REV. A
be
. This voltage is measured by the ADC to give a temperature
o
Temperature
–128∞C
–125∞C
–100∞C
–75∞C
–50∞C
–25∞C
–10
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.
o
C
Table III. Temperature Data Format*
be
, the sensor is switched between operating cur-
I. The resulting waveform is passed through a
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
o
C resolution.
–15–
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 ADM1027 has temperature
offset registers at addresses 0x70, 0x71, and 0x72 for the Remote 1,
Local, and Remote 2 temperature channels. By doing a one-time
calibration of the system, you 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 LSB adds a 1∞C
offset to the temperature reading so the 8-bit register effectively
allows temperature offsets of up to 127∞C with a resolution of
1∞C. This ensures that the readings in the temperature measure-
ment 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 14a. Measuring Temperature Using an
NPN Transistor
Figure 14b. Measuring Temperature Using a
PNP Transistor
2N3904
2N3906
NPN
PNP
D+
D–
D+
D–
ADM1027
ADM1027
ADM1027