ADT7517ARQ Analog Devices Inc, ADT7517ARQ Datasheet - Page 27

• Manufacturer Part Number: ADT7517ARQ
• Description: IC TEMP SNSR QUAD DAC 16-QSOP
• Manufacturer: Analog Devices Inc

Specifications of ADT7517ARQ

• Rohs Status: RoHS non-compliant
• Function: Temp Monitoring System (Sensor)
• Topology: ADC, Comparator, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 120°C, External Sensor
• Output Type: I²C™, MICROWIRE™, QSPI™, SPI™
• Output Alarm: No
• Output Fan: No
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 120°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP

input. If an NPN transistor is used, the emitter is connected to
the D− input and the base to the D+ input.
A 2N3906 is recommended as the external transistor.
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. As the sensor is operating in a noisy
environment, C1 is provided as a noise filter. See the Layout
Considerations section for more information on C1.
To measure ΔV
currents of I and N × I. The resulting waveform is passed
through a low-pass filter to remove noise, then to a chopper
stabilized amplifier that performs the functions of amplification
and rectification of the waveform to produce a dc voltage
proportional to ΔV
give a temperature 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.
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:
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Place the ADT7516/ADT7517/ADT7519 as close as
possible to the remote sensing diode. Provided that the
worst noise sources such as clock generators, data/address
buses, and CRTs are avoided, this distance can be 4 inches
to 8 inches.
Route the D+ and D− tracks close together, in parallel,
with grounded guard tracks on each side. Provide a ground
plane under the tracks, if possible.
Use wide tracks to minimize inductance and reduce noise
pickup. A 10 mil track minimum width and spacing is
recommended.
GND
GND
D+
D–
Figure 54. Arrangement of Signal Tracks
BE
, the sensor is switched between operating
BE
. This voltage is measured by the ADC to
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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 can
be reduced or removed.
Cable resistance can also introduce errors. Series resistance of
1 Ω introduces about 0.5°C error.
Temperature Value Format
One LSB of the ADC corresponds to 0.25°C. The ADC can
theoretically measure a temperature span of 255°C. The internal
temperature sensor is guaranteed to a low value limit of −40°C.
It is possible to measure the full temperature span using the
external temperature sensor. The temperature data format is
shown in Table 9.
The result of the internal or external temperature measurements
is stored in the temperature value registers, and is compared
with limits programmed into the internal or external high and
low registers.
Try to minimize the number of copper/solder joints
because they can cause thermocouple effects. Where
copper/solder joints are used, make sure that they are in
both the D+ and D− path and are at the same temperature.
Thermocouple effects should not be a major problem
because 1°C corresponds to about 240 μV, and
thermocouple voltages are about 3 μV/°C of temperature
difference. Unless there are two thermocouples with a big
temperature differential between them, thermocouple
voltages should be much less than 200 mV.
Place 0.1 μF bypass and 2200 pF input filter capacitors
close to the ADT7516/ADT7517/ADT7519.
If the distance to the remote sensor is more than 8 inches,
the use of twisted-pair cable is recommended. This works
up to about 6 feet to 12 feet.
For long distances (up to 100 feet), use shielded twisted-
pair cable, such as Belden® #8451 microphone cable. Connect
the twisted pair to D+ and D− and the shield to GND, close
to the ADT7516/ADT7517/ADT7519. Leave the remote
end of the shield unconnected to avoid ground loops.
ADT7516/ADT7517/ADT7519