SCF5249VM140 datasheet(31/56 Pages) FREESCALE

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Electrical Characteristics

SCF5249 Integrated ColdFire® Microprocessor Data Sheet, Rev. 3

Freescale Semiconductor

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

Function

GPIO

CMD_SDIO2

GPIO34

SDATA0-SDIO1

GPIO54

RSTO/SDATA2_BS2

A25

GPO8

SCF5249VM140 Datasheet(PDF) 31 Page - Freescale Semiconductor, Inc