mc68hc916y3 Freescale Semiconductor, Inc, mc68hc916y3 Datasheet - Page 226

• Manufacturer Part Number: mc68hc916y3
• Description: Mc68hc16y3 16 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

10.8.4 Accommodating Positive/Negative Stress Conditions
10-18
MOTOROLA
Another approach is to star-point the different grounds near the analog ground pin on
the microcontroller by using small traces for connecting the nonanalog grounds to the
analog ground. The small traces are meant only to accommodate DC differences, not
AC transients.
Other suggestions for PCB layout in which the ADC is employed include the following:
Positive or negative stress refers to conditions which exceed nominally defined oper-
ating limits. Examples include applying a voltage exceeding the normal limit on an in-
put (for example, voltages outside of the suggested supply/reference ranges) or
causing currents into or out of the pin which exceed normal limits. ADC specific con-
siderations are voltages greater than V
input which cause excessive currents into or out of the input. Refer to APPENDIX A
ELECTRICAL CHARACTERISTICS on exact magnitudes.
Both stress conditions can potentially disrupt conversion results on neighboring inputs.
Parasitic devices, associated with CMOS processes, can cause an immediate disrup-
tive influence on neighboring pins. Common examples of parasitic devices are diodes
to substrate and bipolar devices with the base terminal tied to substrate (V
ground). Under stress conditions, current introduced on an adjacent pin can cause er-
rors on adjacent channels by developing a voltage drop across the adjacent external
channel source impedances.
Figure 10-7 shows an active parasitic bipolar when an input pin is subjected to nega-
tive stress conditions. Positive stress conditions do not activate a similar parasitic de-
vice.
• The analog ground must be low impedance to all analog ground points in the cir-
• Bypass capacitors should be as close to the power pins as possible.
• The analog ground should be isolated from the digital ground. This can be done
• Non-minimum traces should be utilized for connecting bypass capacitors and
• Minimum distance for trace runs when possible.
cuit.
by cutting a separate ground plane for the analog ground.
filters to their corresponding ground/power points.
This star-point scheme still requires adequate grounding for digital
and analog subsystems in addition to the star-point ground.
Freescale Semiconductor, Inc.
For More Information On This Product,
ANALOG-TO-DIGITAL CONVERTER
Go to: www.freescale.com
DDA
NOTE
, V
RH
or less than V
SSA
applied to an analog
MC68HC16Y3/916Y3
USER’S MANUAL
SSI
/V
SSA