Texas Instruments LM96080 Evaluation Board LM96080EB/NOPB LM96080EB/NOPB Datenbogen
Produktcode
LM96080EB/NOPB
SNAS465D – SEPTEMBER 2009 – REVISED MARCH 2013
ANALOG INPUTS
The 10-bit ADC has a 2.5 mV (2.56/2
10
) LSb , yielding a 0V to 2.5575V (2.56 - 1 LSb) input range. This is true for
all analog inputs. In most monitoring applications, these inputs would most often be connected to power supplies.
The 2.5, 3.3, ±5 and ±12 volt inputs should be attenuated with external resistors to any desired value within the
input range. Care should be taken not to exceed V
The 2.5, 3.3, ±5 and ±12 volt inputs should be attenuated with external resistors to any desired value within the
input range. Care should be taken not to exceed V
+
at any time.
A typical application, such as is shown in
, might select the input voltage divider to provide 1.9V at the
analog inputs of the LM96080. This is sufficiently high for good resolution of the voltage, yet leaves headroom for
upward excursions from the supply of about 25%. To simplify the process of resistor selection, set the value of
R2 first. Select a value for R2 or R4 between 10 k
upward excursions from the supply of about 25%. To simplify the process of resistor selection, set the value of
R2 first. Select a value for R2 or R4 between 10 k
Ω
and 100 k
Ω
. This is low enough to avoid errors due to input
leakage currents yet high enough to protect both the inputs under overdrive conditions as well as minimize
loading of the source. Then select R1 or R3 to provide a 1.9V input as show in
loading of the source. Then select R1 or R3 to provide a 1.9V input as show in
.
Figure 14. Input Examples. Resistor values shown in table provide approximately 1.9V at the analog
inputs.
Table 2. V
IN
= 1.9V for Different R Values
Voltage Measure-
R1 or R3
R2 or R4
Voltage
ments
at
(V
S
)
Analog Inputs
( ADC code 760)
+2.5V
23.7 k
Ω
75 k
Ω
+1.9V
+3.3V
22.1 k
Ω
30 k
Ω
+1.9V
+5.0V
24 k
Ω
14.7 k
Ω
+1.9V
+12V
160 k
Ω
30.1 k
Ω
+1.9V
−
12V
160 k
Ω
35.7 k
Ω
+1.9V
−
5V
36 k
Ω
16.2 k
Ω
+1.9V
For positive input voltages, the equation for calculating R1 is as follows:
R1 = [ (V
S
−
V
IN
) / V
IN
] R2
(1)
For negative input voltages, the equation for calculating R3 is as follows:
R3 = [ (V
S
−
V
IN
) / (V
IN
−
5V)] R4
(2)
External resistors should be included to limit input currents to the values given in the ABSOLUTE MAXIMUM
RATINGS for Input Current At Any Pin. Inputs with the attenuator networks will usually meet these requirements.
If it is possible for inputs without attenuators to be turned on while LM96080 is powered off, additional resistors of
about 10 k
RATINGS for Input Current At Any Pin. Inputs with the attenuator networks will usually meet these requirements.
If it is possible for inputs without attenuators to be turned on while LM96080 is powered off, additional resistors of
about 10 k
Ω
should be added in series with the inputs to limit the input current.
16
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