CDB5376 Datasheet, PDF (33/78 Pages) Cirrus Logic – Multichannel Seismic Evaluation System

CDB5376
it is recommended to use only the regulated +3.3 V jumper setting for VD. Characterization testing has
shown the VCORE power supply to the digital filter device requires +3 V or higher to operate at the max-
imum 16.384 MHz internal clock rate, so it is recommended to always use the regulated +3.3 V jumper
setting for VCORE.
The VD and VCORE power supplies on CDB5376 include reverse-biased Schottkey diodes to ground to
protect against reverse voltages that could latch-up the CMOS components. Also included on VD and
VCORE are 100 uF bulk capacitors for bypassing and to help settle transients plus individual 0.1 uF by-
pass capacitors local to the digital power supply pins of each device.
2.5 PCB Layout
2.5.1 Layer Stack
CDB5376 layers 1 and 2 are dedicated as analog routing layers. All critical analog signal routes are on
these two layers. Some CPLD and microcontroller digital routes are also included on these layers away
from the analog signal routes.
CDB5376 layer 3 is dedicated for power supply routing. Each power supply net includes at least 100 µF
bulk capacitance as a charge well for settling transient current loads.
CDB5376 layer 4 is a solid ground plane without splits or routing. A soild ground plane provides the best
return path for bypassed noise to leave the system. No separate analog ground is required since analog
signals on CDB5376 are differentially routed.
CDB5376 layers 5 and 6 are dedicated as digital routing layers.
2.5.2 Differential Pairs
Analog signal routes on CDB5376 are differential with dedicated + and - traces. All source and return an-
alog signal currents are constrained to the differential pair route and do not return through the ground
plane. Differential traces are routed together with a minimal gap between them so that noise events affect
them equally and are rejected as common mode noise.
IN+
IN-
Figure 4. Differential Pair Routing
Analog signal connections into the CS3301/02 amplifiers are 2-wire IN+ and IN- differential pairs, and are
routed as such. Analog signal connections out of the CS3301/02 amplifiers and into the CS5372 modu-
DS612DB2
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