Input Buffer Circuit - Texas Instruments ADS8372EVM User Manual

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Polypropylene capacitors cause the least distortion of the input signal and have excellent long-term
stability, but are expensive and bulky. C0G ceramic capacitors cost less, come in smaller packages and
perform as well as polypropylene capacitors in many applications, but are not as stable over time and
temperature. The 68 pF and 6800 pF capacitors installed on the EVM are low-cost C0G type,
manufactured by TDK Corporation.
V
IN
2.2 Reference Voltage
The EVM allows the designer to select internal, on-board, or user-supplied reference-voltage sources. The
internal reference is a 4.096 V reference voltage generated by the ADS8372 on pin 9. The on-board
reference can be either a REF3040 (U1) or REF1004-2.5 (U14). The EVM ships with the REF1004-2.5
installed. The reference amplifier, U3, is set for a gain of 1.6, enabling it to take a 2.5 V input and output
4.1 V for use with the converter, or as part of the common-mode voltage circuit for the input buffer (U13).
The user-supplied reference voltage is applied to connector P1 pin 20, and can be routed through the
reference buffer and filtered, if desired. The EVM allows a number of configurations. Refer to
jumper settings, or the full schematic in
allows users to evaluate this converter with various reference ICs.
The EVM ships with the internal reference tied directly to the reference pin of the converter.
SLAU160 – July 2005
68 pF
1 kW
V
CC
THS4131
1 kW
+ −
2.048 V
_ +
1 kW
−V
CC
1 kW
68 pF
Figure 1. Input Buffer Circuit
Section 9
C0G
0.1 mF
1 mF
25 W
25 W
1 mF
0.1 mF
C0G
for more information. The common footprint for U14
Analog Interface
(+) IN
6800 pF
C0G
(−) IN
Table 1
ADS8372EVM
for
3