ADM1022ARQ-REEL ON Semiconductor, ADM1022ARQ-REEL Datasheet - Page 10

• Manufacturer Part Number: ADM1022ARQ-REEL
• Description: IC SENSOR TEMP/DET 3/5.5V 16QSOP
• Manufacturer: ON Semiconductor
• Type: Temperature Sensorr

Specifications of ADM1022ARQ-REEL

• Rohs Status: RoHS non-compliant
• Input Type: Logic
• Output Type: Analog
• Interface: Serial
• Current - Supply: 2.6mA
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP

ADM1022
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.
To prevent ground noise 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.
If the sensor is used in a very noisy environment, a capacitor of
value up to 1000 pF may be placed between the D+ and D–
inputs to filter the noise.
To measure ∆V
currents of I and N × I. The resulting waveform is passed through
a 65 kHz low-pass filter to remove noise, thence to a chopper-
stabilized amplifier that performs the functions of amplification
and rectification of the waveform to produce a dc voltage pro-
portional to ∆V
a temperature output in 8-bit twos complement format. To fur-
ther reduce the effects of noise, digital filtering is performed by
averaging the results of 16 measurement cycles. An external
temperature measurement takes nominally 9.6 ms.
TRANSISTOR
SENSING
REMOTE
Temperature
–128°C
–125°C
–100°C
–75°C
–50°C
–25°C
–1°C
0°C
+1°C
+10°C
+25°C
+50°C
+75°C
+100°C
+125°C
+127°C
Table II. Temperature Data Format
D+
D–
BE
BE
. This voltage is measured by the ADC to give
, the sensor is switched between operating
I
DIODE
BIAS
N
I
I
BIAS
LOW-PASS
f
C
FILTER
= 65kHz
Digital Output
1000 0000
1000 0011
1001 1100
1011 0101
1100 1110
1110 0111
1111 1111
0000 0000
0000 0001
0000 1010
0001 1001
0011 0010
0100 1011
0110 0100
0111 1101
0111 1111
V
DD
V
V
OUT+
OUT–
ADC
TO
LAYOUT CONSIDERATIONS
Digital boards can be electrically noisy environments, and care
must be taken to protect the analog inputs from noise, particu-
larly when measuring the very small voltages from a remote
diode sensor. The following precautions should be taken:
5. Place 0.1 µF bypass and 1000 pF input filter capacitors close
6. If the distance to the remote sensor is more than eight inches,
7. For really long distances (up to 100 feet) use a shielded
Because the measurement technique uses switched current
sources, excessive cable and/or filter capacitance can affect the
measurement. When using long cables, the filter capacitor C1
may be reduced or removed. In any case, the total shunt capaci-
tance should not exceed 1000 pF.
Cable resistance can also introduce errors. 1 Ω series resistance
introduces about 0.5°C error.
1. Place the ADM1022 as close as possible to the remote sens-
2. Route the D+ and D– tracks close together, in parallel, with
3. Use wide tracks to minimize inductance and reduce noise
4. Try to minimize the number of copper/solder joints, which
ing diode. Provided that the worst noise sources such as
clock generators, data/address buses and CRTs are avoided,
this distance can be four to eight inches.
grounded guard tracks on each side. Provide a ground plane
under the tracks if possible.
pickup. 10 mil track minimum width and spacing is recom-
mended.
can cause thermocouple effects. Where copper/solder joints
are used, make sure that they are in both the D+ and D–
path and at the same temperature.
Thermocouple effects should not be a major problem as 1°C
corresponds to about 200 µV, and thermocouple voltages are
about 3 µV/
two thermocouples with a big temperature differential between
them, thermocouple voltages should be much less than 200 µV.
to the ADM1022.
the use of twisted pair cable is recommended. This will work
up to about 6 to 12 feet.
twisted pair such as Belden #8451 microphone cable. Con-
nect the twisted pair to D+ and D– and the shield to GND
close to the ADM1022. Leave the remote end of the shield
unconnected to avoid ground loops.
GND
GND
D+
D–
o
C of temperature difference. Unless there are
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL