TMS320DM641 datasheet(86/171 Pages) TI

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Power Supplies

June 2003 − Revised August 2004

SPRS222C

4.3

Power Supplies

For more information regarding TI’s power management products and suggested devices to power TI DSPs,

visit www.ti.com/dsppower.

4.3.1

Power-Supply Sequencing

TI DSPs do not require specific power sequencing between the core supply and the I/O supply. However,

systems should be designed to ensure that neither supply is powered up for extended periods of time

(

>1 second) if the other supply is below the proper operating voltage.

4.3.2

Power-Supply Design Considerations

A dual-power supply with simultaneous sequencing can be used to eliminate the delay between core and I/O

power up. A Schottky diode can also be used to tie the core rail to the I/O rail (see Figure 4−5).

DVDD

CVDD

VSS

C6000

DSP

Schottky

Diode

I/O Supply

Core Supply

GND

Figure 4−5. Schottky Diode Diagram

Core and I/O supply voltage regulators should be located close to the DSP (or DSP array) to minimize

inductance and resistance in the power delivery path. Additionally, when designing for high-performance

applications utilizing the C6000

 platform of DSPs, the PC board should include separate power planes for

core, I/O, and ground, all bypassed with high-quality low-ESL/ESR capacitors.

4.3.3

Power-Supply Decoupling

In order to properly decouple the supply planes from system noise, place as many capacitors (caps) as

possible close to the DSP. Assuming 0603 caps, the user should be able to fit a total of 60 caps, 30 for the

core supply and 30 for the I/O supply. These caps need to be close to the DSP power pins, no more than

1.25 cm maximum distance to be effective. Physically smaller caps, such as 0402, are better because of their

lower parasitic inductance. Proper capacitance values are also important. Small bypass caps (near 560 pF)

should be closest to the power pins. Medium bypass caps (220 nF or as large as can be obtained in a small

package) should be next closest. TI recommends no less than 8 small and 8 medium caps per supply (32 total)

be placed immediately next to the BGA vias, using the “interior” BGA space and at least the corners of the

“exterior”.

Eight larger caps (4 for each supply) can be placed further away for bulk decoupling. Large bulk caps (on the

order of 100

µF) should be furthest away (but still as close as possible). No less than 4 large caps per supply

(8 total) should be placed outside of the BGA.

Any cap selection needs to be evaluated from a yield/manufacturing point-of-view. As with the selection of any

component, verification of capacitor availability over the product’s production lifetime should be considered.

TMS320DM641 数据表(PDF) 86 Page - Texas Instruments

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