Datasheet
100
Ω
10k
Ω
9.09k
Ω
10k
Ω
OPA350
OPA365
OPA365
AD S1258
47
Ω
10k
Ω
2.2nF
+2.5V
+2.5V
MU XOUTN
MU XOUTP
ADCINP
ADCINN
−
2.5V
+2.5V
−
2.5V
+2.5V
−
2.5V
AIN15
AINCOM
REFP
REFN
AIN0
AVSS AVDD
±
10V
9.09k
Ω
±
10V
50
Ω
AINx
20m A Input
1k
Ω
1k
Ω
+2 .5V
−
2.5V
0.1
µ
F
100
µ
F 0.1
µ
F
0.47
µ
F
+
10
µ
F
+
REF3125
0.1
µ
F
+
10
µ
F
−
2.5V
0.1
µ
F
+
10
µ
F
…
…
NOTE: 0.1
µ
F capacitors not shown.
47
Ω
ADS1258
SBAS297G –JUNE 2005– REVISED MARCH 2011
www.ti.com
ANALOG INPUT CONNECTIONS When using Auto-Scan mode to sequence through
the channels, the switch time delay feature
Figure 67 shows the ADS1258 interfacing to
(programmable by registers) can be used to provide
high-level ±10V inputs, commonly used in industrial
additional settling time of the external components.
environments. In this case, bipolar power supplies are
used, avoiding the need for input signal level-shifting Figure 68 illustrates the ADS1258 interfacing to
otherwise required when a single supply is used. The multiple pressure sensors having a resistor bridge
input resistors serve both to reduce the level of the output. Each sensor is excited by the +5V single
10V input signal to within the ADC range and also supply that also powers the ADS1258 and likewise is
protect the inputs from inadvertent signal over-voltage used as the ADS1258 reference input; the 6% input
up to 30V. The external amplifiers convert the overrange capability accommodates input levels at or
single-ended inputs to a fully differential output to above V
REF
. The ratiometric connection provides
drive the ADC inputs. Driving the inputs differentially cancellation of excitation voltage drift and noise. For
maintains good linearity performance. The 2.2nF best performance, the +5V supply should be free
capacitor at the ADC inputs is required to bypass the from glitches or transients. The 5V supply input
ADC sampling currents. The 2.5V reference, amplifiers (two OPA365s) form a differential
REF3125, is filtered and buffered to provide a input/differential output buffer with the gain set to 10.
low-noise reference input to the ADC. The chop The chop feature of the ADS1258 is used to reduce
feature of the ADC can be used to reduce offset and offset and offset drift to very low levels. The 2.2nF
offset drift of the amplifiers. capacitor at the ADC inputs is required to bypass the
ADC sampling currents. The 47Ω resistors isolate the
For ±1V input signals, the input resistor divider can
op-amp outputs from the filter capacitor.
be removed and replaced with a series protection
resistor. For 20mA input signals, the input resistor
divider is replaced by a 50Ω resistor, connected from
each input to AINCOM.
Figure 67. Multichannel, ±10V Single-Ended Input, Bipolar Supply Operation
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