Motorola TMS320C6711D - Manual (Page 57)

TMS320C6711D
FLOATINGĆPOINT DIGITAL SIGNAL PROCESSOR
SPRS292A − OCTOBER 2005 − REVISED NOVEMBER 2005
57 POST OFFICE BOX 1443
•
HOUSTON, TEXAS 77251−1443
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 13).
DVDD
CVDD
VSS
C6000
DSP
Schottky
Diode
I/O Supply
Core Supply
GND
Figure 13. 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.
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 (no more than 1.25 cm maximum distance) to the DSP
to be effective. Physically smaller caps are better, such as 0402, but the size needs to be evaluated from a
yield/manufacturing point-of-view. Parasitic inductance limits the effectiveness of the decoupling capacitors,
therefore physically smaller capacitors should be used while maintaining the largest available capacitance
value. As with the selection of any component, verification of capacitor availability over the product’s production
lifetime needs to be considered.