
Power-Supply Sequencing
101
April 2003 Revised June 2004
SPRS219D
2.21
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.
2.21.1
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 214).
DVDD
CVDD
VSS
C6000
DSP
Schottky
Diode
I/O Supply
Core Supply
GND
Figure 214. 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.
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 if the
other supply is below the proper operating voltage.
2.21.2
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, no more than 1.25 cm maximum
distance to be effective. Physically smaller caps are better, such as 0402, but need 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 should be considered.