EVAL-ADT7461EBZ Analog Devices Inc, EVAL-ADT7461EBZ Datasheet - Page 3

• Manufacturer Part Number: EVAL-ADT7461EBZ
• Description: BOARD EVALUATION FOR ADT7461
• Manufacturer: Analog Devices Inc

Specifications of EVAL-ADT7461EBZ

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Power Indicator Green LED D1
When lit, the LED D1 indicates that the ADT7461 evaluation
board is powered.
Therm Indicator Red LED D2
When lit, the LED D2 indicates that the THERM interrupt on
the ADT7461 is active. The LED remains lit until the THERM
interrupt is cleared. For more information on the THERM
functionality, see the ADT7461 data sheet.
ALERT/THERM2 Indicator Red LED D3
The LED D3 lights up when an ALERT/THERM2 interrupt
occurs on the ADT7461, and remains lit until the interrupt is
cleared. For more information on the ALERT/THERM2 pin
and the interrupt functions, see the ADT7461 data sheet.
CONNECTING AN EXTERNAL REMOTE DIODE
SENSOR TO THE EVALUATION BOARD
The user may wish to use an external remote diode sensor with
the ADT7461 evaluation board, instead of the on-board remote
sensor. The user should connect the evaluation board to the
external diode through a twisted pair cable. The connection to
the board should be made through connector J1 at the D+ and
D– pins. LK1 should be set to position A to connect in the
external diode.
MEASURING THE REMOTE DIODE TEMPERATURE
While the ADT7461 has a measurement range of –64°C to
+191°C, the maximum temperature it can measure is limited by
the remote diode selection. Most temperature sensing diodes
stop functioning correctly at about 150°C. More importantly,
they loose their semiconductor characteristics at temperatures
above 150°C, and approximate conductors instead. If this
occurs, the diode will no longer give an accurate temperature
measurement, and the diode short circuit interrupt on the
ADT7461 will be triggered.
Even though the ADT7461 is capable of reading temperatures
up to 191°C, most semiconductor diodes fail beyond 150°C,
and will not give a correct temperature measurement. The user
should note the maximum operating temperature of the remote
temperature sensor. Any temperature measurement gained above
this maximum temperature may be in error. A diode operating
above its maximum temperature may, for example, give a
temperature reading of 75°C instead of an accurate, real
temperature reading of 160°C.
REV. B
–3–
To prevent a potentially dangerous burnout situation, the user
should program the ADT4761 temperature limits to ensure they
are below the maximum operating temperature of the remote
sensor. An interrupt should then be triggered in time for correc-
tive action to be taken to cool the system, before the remote
diode exceeds its maximum operating temperature.
The maximum operating temperature of the 2N3906 remote
diode on the ADT7461 evaluation board is 150°C.
EVALUATING THE ADT7461 SERIES RESISTANCE
CANCELLATION FEATURE
There are two variable resistors on the evaluation board for use
in evaluating the series resistance cancellation feature. One
variable resistor is located in series with the D+ input to the
ADT7461, while the other is located in series with the D– input.
In order to connect both these resistors into the circuit, the
jumpers LK2 and LK3 must be set to position B.
Varying the resistors adds resistance in series with the remote
diode. The normal consequence of increased series resistance is
to add an offset to the temperature being measured. However,
the ADT7461 automatically cancels out the effect of the series
resistance, so the temperature of the remote diode should not
change with increased series resistance. For more information
on series resistance cancellation, see the ADT7461 datasheet.
If the user has both variable resistors connected in to the evalua-
tion circuit, then the total resistance being cancelled by the
ADT7461 is the sum of both resistances. If only one of the
variable resistors is connected in, then the total resistance being
cancelled is the value of that resistance only. The maximum
resistance of both R
able resistance of 4 kΩ.
The user should see that the temperature measurement given by
the ADT7461 remains constant while the variable resistances
are changed. As the total series resistance value is increased
above a certain value (1 kΩ typ), a jump in the temperature
measurement will occur, signifying that the series resistance
cancellation has reached its threshold and is no longer cancel-
ling resistance.
VAR1
and R
VAR1
is 2 kΩ, giving a total avail-
EVAL-ADT7461