Datasheet
ADS8528
ADS8548
ADS8568
SBAS543A –AUGUST 2011– REVISED OCTOBER 2011
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POWER SUPPLY
The ADS8528/48/68 require four separate supplies: an analog supply for the ADC (AVDD), the buffer I/O supply
for the digital interface (DVDD), and the high-voltage supplies driving the analog input circuitry (HVDD and
HVSS). Generally, there are no specific requirements with regard to the power sequencing of the device.
However, when HVDD is supplied before AVDD, the internal electrostatic discharge (ESD) structure conducts,
increasing the IHVDD beyond the specified value, until the AVDD is applied.
The AVDD supply provides power to the internal circuitry of the ADC. If run at maximum data rate, the IAVDD is
too high to allow use of a passive filter between the digital board supply of the application and the AVDD pins. A
linear regulator is recommended to generate the analog supply voltage. Each AVDD pin should be decoupled to
AGND with a 100nF ceramic capacitor. In addition, a single 10µF capacitor should be placed close to the device
but without compromising the placement of the smaller capacitors. Optionally, each supply pin can be decoupled
using a 1µF ceramic capacitor without the requirement for the additional 10µF capacitor.
The DVDD supply is only used to drive the digital I/O buffers and allows seamless interface with most
state-of-the-art processors and controllers. As a result of the low IDVDD value, a 10Ω series resistor can be used
on the DVDD pin to reduce the noise energy from the external digital circuitry influencing the performance of the
device. A bypass ceramic capacitor of 1µF (or alternatively, a pair of 100nF and 10µF capacitors) should be
placed between pins 24 and 25.
The high-voltage supplies (HVSS and HVDD) are connected to the analog inputs. These supplies are not
required to be of symmetrical nature with regard to AGND. Noise and glitches on these supplies directly couple
into the input signals. Place a 100nF ceramic decoupling capacitor, located as close to the device as possible,
between each of pins 1, 48, and AGND. An additional 10µF capacitor is used that should be placed close to the
device but without compromising the placement of the smaller capacitors.
Figure 44 shows a layout recommendation for the ADS8528/48/68 along with the proper decoupling and
reference capacitors placement and connections. The layout recommendation takes into account the actual size
of the components used.
40 Copyright © 2011, Texas Instruments Incorporated
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