ADS8528_14 Datasheet, PDF (38/52 Pages) Texas Instruments – 12-, 14-, 16-Bit, Eight-Channel, Simultaneous Sampling ANALOG-TO-DIGITAL CONVERTERS

ADS8528
ADS8548
ADS8568
SBAS543A – AUGUST 2011 – REVISED OCTOBER 2011
APPLICATION INFORMATION
www.ti.com
TYPICAL APPLICATION EXAMPLE
An example of a typical application of the ADS8528/48/68 is illustrated in Figure 43. In this case, the device is
used to simultaneously sample and convert the voltages and currents on three phases and the neutral line. In
this example, the BUSY signal is not used by the controller while the SW generates the required signals in timely
manner. TI’s OPA2211 is used as an input driver, supporting bandwidth that allows running the device at the
maximum data rate. However, because relatively low data rates are generally used in this type of applications,
the auto-sleep mode is activated in this example (ASLEEP is high) to minimize the current demand on the AVDD
and HVDD/HVSS power supplies. Further, the input drivers may not be necessary if the signal source fulfills the
requirements as defined by Equation 2. For example, at 10kSPS, the external drivers are not necessary if the
source impedance remains below 830kΩ in ±4VREF mode or 415kΩ in ±2VREF mode.
While the actual values of the resistors and capacitors depend on the bandwidth and performance requirements
of the application, for a data rate of 10kSPS, it is recommended to use a filter capacitor C_F value of 1nF and a
series resistor R_F of 10kΩ.
In applications supporting only single supply (for example, 5V), it is recommended to use the TPS65130 to
generate the bipolar supplies required by the ADC.
GROUNDING
All ground pins should be connected to a clean ground reference. This connection should be kept as short as
possible to minimize the inductance of these paths. It is recommended to use vias connecting the pads directly to
the corresponding ground plane. In designs without ground planes, the ground trace should be kept as wide and
as short as possible to reduce inductance. Avoid connections that are too close to the grounding point of a
microcontroller or digital signal processor.
Depending on the circuit density on the board, placement of the analog and digital components, and the related
current loops, a single solid ground plane for the entire printed circuit board (PCB) or dedicated analog and
digital ground areas may be used. In case of separated ground areas, ensure a low-impedance connection
between the analog and digital ground of the ADC by placing a bridge underneath (or next to) the ADC.
Otherwise, even short undershoots on the digital interface with a value of lower than –300mV lead to the
conduction of ESD diodes, causing current to flow through the substrate and either degrading the analog
performance or even damaging the part. It is recommended to use a common ground plane underneath the
device as a local ground reference for all xGND pins; see Figure 44. During PCB layout, care should be taken to
avoid any return currents crossing sensitive analog areas or signals.
38
Copyright © 2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8528 ADS8548 ADS8568