EVAL-ADM1023EB ON Semiconductor, EVAL-ADM1023EB Datasheet - Page 7

• Manufacturer Part Number: EVAL-ADM1023EB
• Description: BOARD EVAL FOR ADM1023
• Manufacturer: ON Semiconductor
• Type: Temperature Sensorr

Specifications of EVAL-ADM1023EB

• Contents: Evaluation Board
• For Use With/related Products: ADM1023
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Theory of Operation
Functional Description
converter (ADC) with special input−signal conditioning to
enable operation with remote and on−chip diode
temperature sensors. When the ADM1023 is operating
normally, the ADC operates in a free−running mode. The
analog input multiplexer alternately selects either the
on−chip temperature sensor to measure its local temperature
or the remote temperature sensor. These signals are digitized
by the ADC, and the results are stored in the local and remote
temperature value registers. Only the eight most significant
bits (MSBs) of the local temperature value are stored as an
8−bit binary word. The remote temperature value is stored
as an 11−bit binary word in two registers. The eight MSBs
are stored in the remote temperature value high byte register
at Address 0x01. The three least significant bits (LSBs) are
stored, left justified, in the remote temperature value low
byte register at Address 0x10.
can introduce offset errors into measurements on the remote
channel. To achieve the specified accuracy on this channel,
these offsets must be removed, and two offset registers are
provided for this purpose at Address 0x11 and Address
0x12.
subtracted from the measurement by writing an 11−bit, twos
complement value to Register 0x11 (high byte) and Register
0x12 (low byte, left−justified).
effect if nothing is written to them.
remote, high and low temperature limits, stored in six
Measurement Method
the negative temperature coefficient of a diode, or the base
emitter voltage of a transistor, operating at constant current.
Thus, the temperature may be obtained from a direct
measurement of V
The ADM1023 contains a two−channel analog−to−digital
Error sources such as PCB track resistance and clock noise
An offset value may automatically be added to or
The offset registers default to 0 at powerup and have no
The measurement results are compared with local and
A simple method of measuring temperature is to exploit
TRANSISTOR
SENSING
REMOTE
BE
where:
V
BE
+ nKT
q
C1
D+
D–
1
1n
I
Figure 13. Input Signal Conditioning
I
I
C
S
DIODE
N y I
BIAS
(eq. 1)
http://onsemi.com
ADM1023
I
BIAS
LOW−PASS FILTER
f
7
C
= 65kHz
1
CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS.
C1 = 1000pF MAX.
on−chip limit registers. As with the measured value, the
local temperature limits are stored as 8−bit values and the
remote temperature limits as 11−bit values. Out−of−limit
comparisons generate flags that are stored in the status
register, and one or more out−of−limit results cause the
ALERT output to pull low.
and configured, via the serial system management bus
(SMBus). The contents of any register can also be read back
via the SMBus.
•
•
•
values default to −128°C. The device normally powers up
converting, making a measure of local and remote
temperature. These values are then stored before making a
comparison with the stored limits. However, if the part is
powered up in standby mode (STBY pin pulled low), no new
values are written to the register before a comparison is
made. As a result, both RLOW and LLOW are tripped in the
status register, thus generating an ALERT output. This may
be cleared in one of two ways:
•
•
the effect of the absolute value of V
device to device.
change in V
collector currents.
Registers can be programmed, and the device controlled
Control and configuration functions consist of:
On initial powerup, the remote and local temperature
This technique, however, requires calibration to nullify
The technique used in the ADM1023 is to measure the
Switching the device between normal operation and
standby mode.
Masking or enabling the ALERT output.
Selecting the conversion rate.
Change both the local and remote lower limits to
–128°C and read the status register (which in turn
clears the ALERT output).
Take the part out of standby and read the status register
(which in turn clears the ALERT output). This works
only when the measured values are within the limit
values.
V
DD
BE
when the device is operated at two different
BE
V
V
TO ADC
OUT+
OUT–
, which varies from