AVDD
RSEL
VREF
0.5V
+
Output
0.1µF
2.2µF
RSEL
VREF
402Ω
+3.3V
Input
0.5V to 1V
ADS5220
+
REFT
0.1µF
2.2µF
+
+
2Ω
10µF
2.2µF
2.2µF
15µF
15µF
402Ω
ADS5220
REFT
+3.3V
2Ω
REFB
+
+
+
+
2Ω
10µF
2.2µF
2.2µF
15µF
15µF
402Ω
2Ω
REFB
FIGURE 8. Internal Reference Mode for VREF = 0.5V.
402Ω
FIGURE 10. External Reference Configuration.
RSEL
R2
VREF
DIGITAL OUTPUTS
DATA OUTPUT FORMAT
+
0.1µF
2.2µF
R1
402Ω
The ADS5220 makes two data output formats available,
either the Straight Offset Binary (SOB) code or the Binary
Two’s Complement (BTC) code. The selection of the output
coding is controlled through the MSBI pin. Applying a logic
high will enable the BTC coding, whereas a logic low will
enable the SOB code. In its default configurations the MSBI
pin assumes a logic low level (internal pull-down) and the
ADS5220 will operate with the SOB output coding. The two
code structures are identical with one exception: the MSB is
inverted for the BTC format, as shown in Table II. If the input
signal exceeds the FSR, the output code will remain at all 1s
or all 0s.
ADS5220
REFT
+3.3V
+
+
+
2Ω
10µF
2.2µF
2.2µF
15µF
2Ω
REFB
15µF
402Ω
FIGURE9. InternalReferenceModeforVREF =0.5•(1+R2/R1).
EXTERNAL REFERENCE
For even more design flexibility, the ADS5220 can be oper-
ated with external references. Utilization of an external refer-
ence voltage may be considered for applications requiring
higher accuracy, improved temperature stability, or flexible
full-scale range. Particularly in multi-channel applications,
the use of a common external reference offers the benefit of
improving gain matching between converters. Setting RSEL
to AVDD (+3.3V) provides an external reference mode for the
ADS5220. In this case, the internal VREF amplifier is powered
down, and the VREF pin requires an external reference
voltage between +0.5V to +1V to provide an input full-scale
range of 1VPP to 2VPP. The REFT and REFB will appear with
the voltage as shown in Table I, and input FSR is always
twice the voltage at the VREF pin. A voltage reference
(REF1004 or TPS79225) and a single-supply amplifier
(OPA2234 or OPA4227) can be used to generate a precision
external reference.
BINARY TWO’S
COMPLEMENT
(BTC)
STRAIGHT OFFSET
BINARY (SOB)
DIFFERENTIAL INPUT
+FS – 1LSB
1111 1111 1111
1100 0000 0000
1000 0000 0000
0100 0000 0000
0000 0000 0000
0111 1111 1111
0100 0000 0000
0000 0000 0000
1100 0000 0000
1000 0000 0000
(+FS: IN = 2V,
+1/2 FS
= 1V)
IN
(IN = 1.75V,
= 1.25V)
IN
Bipolar Zero
(IN =
= 1.5V)
IN
–1/2 FS
(
= 1.75V, IN = 1.25V)
= 2V, IN = 1V)
IN
–FS
(
IN
TABLE II. Coding Table for Differential Input Configuration
with FSR of 2VPP
.
ADS5220
14
SBAS261A
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