Electrical Characteristics
Figure 3. Example Circuit to Control Supply Sequencing
When a DC-DC convertor is used in the system to generate the 1.8V supply, additional care is required. If
possible, the 1.8V DC-DC convertor should be supplied by the 3.3V supply. If this is impossible or
considered inefficient, the designer needs to ensure that the rise time of the 1.8V supply still complies with
the recommendations stated above. Adding the 3 diodes will help resolve issues associated with a slow rise
time of the 1.8V supply. Further, a Schotty diode could be added between the supplies, which would have
the effect of holding the 1.8V supply to match the 3.3V supply should the 1.8V supply come-up first. This
diode also has the function of ensuring that there is not a large voltage differential between the Core supply
and the PAD supply during power-down.
Refer to the
M5249C3 Reference Board Userís Manual
for the recommended diode types.
A further note is the recommendation for hard resetting of the device. Freescale recommends using a
dynamic reset circuit. This allows for control of the voltage at which the reset will be released and ensure
that the correct voltage level at the RESET pin is achieved in all cases. Passive (RC) reset networks do not
always achieve the desired results.
Figure 4. SCF5249 Power Supply
NOTE
The following signals are not available on the 144 QFP package.
Table 18. 160 MAPBGA Ball Assignments
160MAPBGA Ball
Number
E3
G4
H3
K3
Function
CMD_SDIO2
SDATA0-SDIO1
RSTO/SDATA2_BS2
A25
GPO8
GPIO
GPIO34
GPIO54
SCF5249 Integrated ColdFire® Microprocessor Data Sheet, Rev. 3
Freescale Semiconductor
31
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
