QADC64E Enhanced Mode Operation
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
14-69
Figure 14-49. Star-Ground at the Point of Power Supply Origin
Another approach is to star-point the different grounds near the analog ground signal on the
microcontroller by using small traces for connecting the non-analog grounds to the analog ground. The
small traces are meant only to accommodate DC differences, not AC transients.
NOTE
This star-point scheme still requires adequate grounding for digital and
analog subsystems in addition to the star-point ground.
Other suggestions for PCB layout in which the QADC64E is employed include:
•
Analog ground must be low impedance to all analog ground points in the circuit.
•
Bypass capacitors should be as close to the power signals as possible.
•
The analog ground should be isolated from the digital ground. This can be done by cutting a
separate ground plane for the analog ground.
•
Non-minimum traces should be utilized for connecting bypass capacitors and filters to their
corresponding ground/power points.
•
Distance for trace runs should be minimized where possible.
14.6.4
Analog Reference Signals
V
RH
and V
RL
are the dedicated input signals for the high and low reference voltages. Separating the
reference inputs from the power supply signals allows for additional external filtering, which increases
reference voltage precision and stability, and subsequently contributes to a higher degree of conversion
accuracy.
QADC64E
VR
H
VR
L
VSSA
VD
D
A
VDD
VSS
Analog Power Supply
+5V
+5V
AGND
Digital Power
+5V
PGND
PCB
Supply
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...