EVAL-ADM1026EB ON Semiconductor, EVAL-ADM1026EB Datasheet - Page 17

• Manufacturer Part Number: EVAL-ADM1026EB
• Description: BOARD EVAL FOR ADM1026
• Manufacturer: ON Semiconductor
• Type: Temperature Sensorr

Specifications of EVAL-ADM1026EB

• Contents: Evaluation Board
• For Use With/related Products: ADM1026
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Voltage Measurement Inputs
Figure 26. Each input circuit consists of an input protection
diode, an attenuator, plus a capacitor to form a first−order
low−pass filter that gives each voltage measurement input
immunity to high frequency noise. The −12 V input also has
a resistor connected to the on−chip reference to offset the
negative voltage range so that it is always positive and can
be handled by the ADC. This allows most popular power
supply voltages to be monitored directly by the ADM1026
without requiring any additional resistor scaling.
Setting Other Input Ranges
2.5 V or 3.0 V. If the input voltage range is zero to some
positive voltage, all that is required is an input attenuator, as
shown in Figure 27.
that these inputs already have an on−chip attenuator,
The internal structure for all the analog inputs is shown in
A
However, when scaling A
IN0
A
A
(0V – 2.5V)
IN0
(0V – 3V)
IN6
to A
Figure 26. Voltage Measurement Inputs
– A
– A
+V
–12V
+12V
V
+5V
CCP
IN5
BAT
IN9
IN9
Figure 27. Scaling A
V
IN
can easily be scaled to voltages other than
* SEE TEXT
113.5kΩ
114.3kΩ
21.9kΩ
52.5kΩ
83.5kΩ
49.5kΩ
21.9k
109.4kΩ
109.4kΩ
82.7kΩ
50kΩ
21kΩ
R1
17.5kΩ
V
IN0
REF
to A
A
IN0
IN(0–9)
R2
IN5
4.6pF
4.5pF
4.6pF
9.3pF
9.3pF
4.6pF
18.5pF
− A
, it should be noted
IN9
MUX
http://onsemi.com
17
because their primary function is to monitor SCSI
termination voltages. This attenuator loads any external
attenuator. The input resistance of the on−chip attenuator
can be between 100 kW and 200 kW. For this tolerance not
to affect the accuracy, the output resistance of the external
attenuator should be very much lower than this, that is, 1 kW
in order to add not more than 1% to the total unadjusted error
(TUE). Alternatively, the input can be buffered using an op
amp.
by using a positive reference voltage to offset the input
voltage range so that it is always positive. To monitor a
negative input voltage, an attenuator can be used as shown
in Figure 28.
sees a positive voltage. R1 and R2 are chosen so that the
ADC input voltage is zero when the negative input voltage
is at its maximum (most negative) value, that is:
following:
•
•
when the negative voltage is zero.
Negative and bipolar input ranges can be accommodated
This offsets the negative voltage so that the ADC always
This is a simple and low cost solution, but note the
This is a problem only if the ADC output must be full scale
Because the input signal is offset but not inverted, the
input range is transposed. An increase in the magnitude
of the negative voltage (going more negative) causes the
input voltage to fall and give a lower output code from
the ADC. Conversely, a decrease in the magnitude of the
negative voltage causes the ADC code to increase. The
maximum negative voltage corresponds to zero output
from the ADC. This means that the upper and lower
limits are transposed.
For the ADC output to be full scale when the negative
voltage is zero, V
voltage of the ADC, because V
R2. If V
of the ADC, the input range is bipolar but not necessarily
symmetrical.
Figure 28. Scaling and Offsetting A
R1
R2
R1
R2
R1
R2
+
+
+
OS
V
V
V
is equal to or less than the full−scale voltage
V
f s
f s
f s
OS
3.0
2.5
*
* 3.0
* 2.5
V
IN
for Negative Inputs
OS
must be greater than the full−scale
for A
for A
R1
R2
IN0
IN6
OS
through A
through A
A
IN(0–9)
is attenuated by R1 and
IN0
IN5
IN9
− A
IN9
(eq. 4)
(eq. 2)
(eq. 3)