Datasheet

ADS803
10
SBAS074B
www.ti.com
3.5V
1.5V
IN
IN
+1V
SELV
REF
+2.5V ext.
ADS803
V
IN
V
IN
5V
0V
IN
IN
+2.5V
SELV
REF
ADS803
FIGURE 8. Internal Reference with 1.5V to 3.5V Input Range.
FIGURE 9. Internal Reference with 1V to 4V Input Range.
FIGURE 7. Internal Reference with 0V to 5V Input Range.
The top reference (REFT) and the bottom reference (REFB)
are brought out mainly for external bypassing. For proper
operation with all reference configurations, it is necessary to
provide solid bypassing to the reference pins in order to keep
the clock feedthrough to a minimum. Figure 5 shows the
recommended decoupling network.
4V
1V
IN
IN
SELV
REF
+2.5V ext.
V
REF
= 1V 1 +
R
1
R
2
FSR = 2 • V
REF
ADS803
R
1
5kΩ
+1.5V
R
2
10kΩ
FIGURE 5. Recommended Reference Bypassing Scheme.
ADS803
CMREFB
0.1µF
0.1µF
V
REF
0.1µF
10µF
+
0.1µF
REFT
0.1µF
10µF
+
FIGURE 6. Alternative Circuit to Generate CM Voltage.
IN
IN
REFT
R
1
CMV
R
2
0.1µF
0.1µF
ADS803
REFB
In addition, the common-mode voltage (CMV) may be used as
a reference level to provide the appropriate offset for the driving
circuitry. However, care must be taken not to appreciably load
this node, which is not buffered and has a high impedance. An
alternate method of generating a common-mode voltage is
given in Figure 6. Here, two external precision resistors (toler-
ance 1% or better) are located between the top and bottom
reference pins. The common-mode level will appear at the
midpoint. The output buffers of the top and bottom reference
are designed to supply approximately 2mA of output current.
SELECTING THE INPUT RANGE AND REFERENCE
Figures 7 through 9 show a selection of circuits for the most
common input ranges when using the internal reference of
the ADS803. All examples are for single-ended inputs and
operate with a nominal common-mode voltage of +2.5V.
EXTERNAL REFERENCE OPERATION
Depending on the application requirements, it might be
advantageous to operate the ADS803 with an external refer-
ence. This may improve the DC accuracy if the external