Datasheet
100
Ω
10k
Ω
9.09k
Ω
10k
Ω
OPA350
OPA365
OPA365
AD S1258
47
Ω
10k
Ω
2.2n F
+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
+
REF 3125
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-EP
SBAS445D –MARCH 2009– 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 68 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 69 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 5-V 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 2.2-nF best performance, the 5-V supply should be free from
capacitor at the ADC inputs is required to bypass the glitches or transients. The 5-V supply input amplifiers
ADC sampling currents. The 2.5-V reference, (two OPA365s) form a differential input/differential
REF3125, is filtered and buffered to provide a output buffer with the gain set to 10. The chop feature
low-noise reference input to the ADC. The chop of the ADS1258 is used to reduce offset and offset
feature of the ADC can be used to reduce offset and drift to very low levels. The 2.2-nF capacitor at the
offset drift of the amplifiers. ADC inputs is required to bypass the ADC sampling
currents. The 47-Ω resistors isolate the op-amp
For ±1V input signals, the input resistor divider can
outputs from the filter capacitor.
be removed and replaced with a series protection
resistor. For 20-mA input signals, the input resistor
divider is replaced by a 50-Ω resistor, connected from
each input to AINCOM.
Figure 68. Multichannel, ±10V Single-Ended Input, Bipolar Supply Operation
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