Datasheet
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Analog Interface
Following the THS4520, an R-C network connects directly to the ADS1672. This R-C network (R56, R15,
C18, R55, and R14) acts as a first-order, anti-aliasing filter for the ADS1672. The corner frequency of the
installed first-order filter is 1/[2 π × (10 Ω + 10 Ω ) × 750pF] or 10.6MHz. Pads are available to install more
resistors and capacitors, as needed.
The common-mode voltage to the THS4520 is set at R
CM
and can be connected to the analog board
inputs +IN and –IN through R53 and R54 as shown in Figure 2 . The output signal from the onboard
REF5025 (U3) establishes this voltage at 2.5V. You can inject an external common-mode voltage into the
THS4520 through P3-15 (as Table 1 shows). If this option is used, the shunt on W1 (an onboard jumper)
must be moved to position 2-3 (see Figure 1 ). With this reconfiguration, R
CM
in the input circuitry does not
change, as shown in Figure 2 . If the common-mode of the input signals center at a voltage other than
VCC/2, pull-up resistors (R48 and R49) must be installed to maintain the proper input common-mode
range to the THS4520 amplifier. The THS4520 performance degrades if operated beyond its specified
range of 1.2V to 4.25V (when powered with 5V).
Samtec part number TSM-110-01-T-DV-P provides a convenient 20-pin, dual-row, header/socket
combination at P3. As shown in Figure 1 , the P3 header provides access to –IN and +IN of the
ADS1672EVM board as well as the common-mode pins of the THS4520 (pins 4 and 9, CM). Consult
Samtec at http://www.samtec.com or call 1-800-SAMTEC-9 for a variety of mating connector options.
There is no filtering or protection on the P3 pins. Use appropriate caution when handling these pins.
Table 1 summarizes the pin assignments for the analog interfaces on P3.
Table 1. P3: External Analog Input Connector
Pin Number Signal Description
P3.1 –IN Inverting analog input
P3.2 +IN Noninverting analog input
P3.3 NC No connection
P3.4 NC No connection
P3.5 NC No connection
P3.6 NC No connection
P3.7 NC No connection
P3.8 NC No connection
P3.9 NC No connection
P3.10 NC No connection
P3.11 GND System ground
P3.12 NC No connection
P3.13 GND System ground
P3.14 NC No connection
External common-mode voltage; connect
P3.15 EXT_COM
to THS4520
P3.16 NC No connection
P3.17 GND System ground
P3.18 NC No connection
P3.19 GND System ground
P3.20 NC No connection
SBAU147 – March 2009 ADS1672EVM and ADS1672EVM-PDK User's Guide 5
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