MPC561MZP56 Freescale, MPC561MZP56 Datasheet - Page 534

• Manufacturer Part Number: MPC561MZP56
• Manufacturer: Freescale

Specifications of MPC561MZP56

• Cpu Family: MPC56x
• Device Core: PowerPC
• Device Core Size: 32b
• Frequency (max): 56MHz
• Interface Type: QSPI/SCI/SPI/UART
• Total Internal Ram Size: 32KB
• # I/os (max): 56
• Number Of Timers - General Purpose: 22
• Operating Supply Voltage (typ): 2.6/5V
• Operating Supply Voltage (max): 2.7/5.25V
• Operating Supply Voltage (min): 2.5/4.75V
• On-chip Adc: 2(32-chx10-bit)
• Instruction Set Architecture: RISC
• Operating Temp Range: -40C to 125C
• Operating Temperature Classification: Automotive
• Mounting: Surface Mount
• Pin Count: 388
• Package Type: BGA
• Program Memory Type: ROMLess
• Program Memory Size: Not Required
• Lead Free Status / RoHS Status: Not Compliant

QADC64E Legacy Mode Operation
The problem of how and when to combine digital and analog grounds arises from the large transients
which the digital ground must handle. If the digital ground is not able to handle the large transients, the
current from the large transients can return to ground through the analog ground. It is the excess current
overflowing into the analog ground which causes performance degradation by developing a differential
voltage between the true analog ground and the microcontroller’s ground signal. The end result is that the
ground observed by the analog circuit is no longer true ground and often ends in skewed results.
Two similar approaches designed to improve or eliminate the problems associated with grounding excess
transient currents involve star-point ground systems. One approach is to star-point the different grounds at
the power supply origin, thus keeping the ground isolated. Refer to
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.
Other suggestions for PCB layout in which the QADC64E is employed include:
The analog ground should be isolated from the digital ground. This can be done by cutting a separate
ground plane for the analog ground
13-70
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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.
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
This star-point scheme still requires adequate grounding for digital and
analog subsystems in addition to the star-point ground.
MPC561/MPC563 Reference Manual, Rev. 1.2
NOTE
Figure
13-51.
Freescale Semiconductor