Special Notes on Connectivity
8
SPRUI76A – March 2017 – Revised January 2019
Copyright © 2017–2019, Texas Instruments Incorporated
Delfino™ TMS320F28379D controlCARD R1.3
In addition to the quality of the input signal, there is also the aspect of the load presented to the ADC
when it samples the input. Ideally, an input to an ADC would have zero impedance so as not to impact the
internal R/C network when the sampling event takes place. In many applications, however, the voltages
that are sampled by the ADC are derived from a series of resistor networks that are often large in value to
decrease the active current consumption of the system. A solution to isolate the source impedance from
the ADC sampling network is to place an operational amplifier in the signal path. Not only does this isolate
the impedance of the signal from the ADC, it also shields the source itself from any effects the sampling
network may have on the system.
Recommended source for evaluation:
The
Precision Signal Injector (PSI) EVM
from TI was used to
validate the ADC performance on the F28379D ControlCARD. This EVM supports both single ended as
well as differential ended outputs using a
16-bit digital-to-analog converter (DAC)
as the signal source
then passed through a
with post amplifier filtering. The EVM is powered and
controlled through a standard USB connection from a host PC and includes a GUI to control its output.
The outputs are routed through single or dual SMA type connectors. It is highly recommended to place
additional female SMA connectors (
) on the controlCARD docking station to receive the signal via
SMA cable for best noise immunity. For the local RC network, 30-
Ω
resistors and 300 pF capacitors were
used. Using this setup, the ADC parameters were observed to be consistent with the published numbers
in the
TMS320F2837xD Dual-Core Delfino™ Microcontrollers
.
Figure 5. Female SMA Connector