
7.3 Voltage Plane Power Requirements
7.4 Power Supply Layout Recommendations
7.5 Voltage Tolerances, Noise, and Transients
7.5.1 Using Remote Sense Power Supplies
Power Supply
Although the power sequence has 3.3V I/O ramping before the core voltage, bus contention will not occurin this case due to special circuitry that has been added that hold the 3.3V I/Os in tri-state during thepower ramp-up period.
There are multiple ways to generate a controlled power sequence. A microcontroller or PLD can be usedto control power supply sequencing. Alternatively, TI has power management products that can be usedsuch as the TPS3808 (http://focus.ti.com/lit/ds/symlink/tps3808g33.pdf ).
Power requirements are highly dependent on the usage of the device. This includes which peripherals areused as well as the operating frequencies. In order to generate an estimate of the TCI6482 power for aparticular application, refer to the TMS320TCI6482 Preliminary Power Consumption Summary.
Core and I/O supply voltage regulators should be located close to the DSP (or DSP array) to minimizeinductance and resistance in the power delivery path. Additionally, when designing for high-performanceapplications utilizing the C6000 platform of DSPs, the PCB should include separate power planes for core,I/O and ground, all bypassed with high-quality low-ESL/ESR capacitors.
For VREFHSTL and VREFSSTL, one reference voltage divider should be used for both the TCI6482 andthe reference voltage input on the attached device. The same supply should also be used for the I/Ovoltages between the 2 parts. The VREF resistor divider should be placed between the 2 devices and theroutes made as directly as possible with a minimum 20 mil wide trace. There should be a 2x trace widthclearance between the routing of the reference voltage and any switching signals.
The DLL signals (AVDLL1 and AVDLL2) can be routed using minimum 15 mil wide traces. There shouldbe a 2x trace width clearance between this and any switching signals.
The filter circuits should be placed as close to the corresponding TCI6482 power supply pin(s) aspossible. No digital switching signals should be routed near or directly under the filter circuits.
The voltage tolerances specified in the datasheet include all DC tolerances and the transient response ofthe power supply. These specify the absolute maximum and minimum levels that must be maintained atthe pins of the TCI6482 under all conditions. Special attention to the power supply solution is needed toachieve this level of performance, especially the 3% tolerance on the core power plane (CVDD).
In order to maintain the 3% tolerance at the pins, the tolerance must be a combination of the power supplyDC output accuracy, the voltage drop from the supply to the load and the effect of transients. Areasonable goal for the DC power supply output accuracy is 1.5%, leaving 1.5% for the transients. At 1.2Va 3% tolerance is +/-36mV. This allows 18mV of DC accuracy from the output of the power supply andanother 18mV due to transients.
Power plane IR drop is another factor to consider, especially if there are multiple DSPs in a group on aboard. Power planes, even if no splits are present, have impedance. With large currents running acrossthe power planes the voltage drop must be considered. This same issue also applies to ground planeswith heavy currents.
Use of a power supply that supports the remote sense capability allows the power supply to control thevoltage at the load. Special layout care must be used to keep this sense trace from being lost during PCBlayout. One solution is placement of a small resistor at the load and connecting the sense trace to thevoltage plane through it. If a group of DSPs on the board are supplied by a single core power supply, thesense resistor should be placed at the center of this group. If a negative sense pin is supported by thevoltage regulator it should be handled in a similar way. An example of this type of implementation isshown in Figure 10 .
SPRAAC7B – April 2006 TMS320TCI6482 Design Guide and Migration from TMS320TCI100 17Submit Documentation Feedback