双电源供电DSP上电顺序解决方案.pdf

Application Report

SLVA073A - July 2000

1

Power Supply Sequencing Solutions for Dual Supply

Voltage DSPs

Mixed Signal Products

ABSTRACT

This application report describes power-supply sequencing recommendations and

techniques applicable to dual supply voltage DSPs in TI’s TMS320C2000, TMS320C5000

2 Core and I/O Supply Sequencing Options 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 References 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 Dual Supplies With Bootstrap Schottky Diode 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 Power Sequencing Using the TPS2034 and Power Good Signal 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6 Power Sequencing Using the TPS2024 and Single SVS With RESET 12. . . . . . . . . . . . . . . . . . . . . . . . .

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The use of dual power supply voltages is common in TI’s high-performance DSPs. TI offers power

management products to address these power supply requirements, and those of many other

systems. This application report discusses sequencing requirements and recommendations for TI

DSPs, and presents options for sequencing power supply voltages in typical DSP applications. The

discussion and that the exact power supply requirements, e.g., maximum output current, output

voltage tolerance, output voltage ripple, efficiency, etc., must be considered in the power supply

selection or design process. It is also important to note that decoupling capacitors are not shown

but should be included as needed.

Many power supply configurations are possible for powering TI’s dual supply voltage DSPs,

depending on the voltage(s) available from the system for use as input power, and the configuration

of the DSP application (i.e., how many DSPs, how much other circuitry, etc.). This report addresses

sequencing solutions for the following:

in the starting point and ramp rates of the two supplies may cause current to flow in the isolation

structures which, when prolonged and excessive, can reduce the useable life of the semiconductor

device. These currents can also trigger latch-up in devices designed with inadequate latch-up

protection. TI DSPs tolerate a wide range of conditions during power up. However, some control of

the power-up and power-down sequencing deserves consideration to enhance short and long term

reliability of the entire system. The following note, which is included in the data sheets for dual supply

voltage DSPs, presents TI’s requirements with regard to power supply sequencing:

NOTE: TI DSPs do not require specific power sequencing between the core supply

and the I/O supply. However, systems should be designed to insure that neither

supply is powered up for extended periods of time if the other supply is below the

high current state may damage the device if the condition exists for an extended

period of time (several seconds). A normal current state will return once the I/O

power supply is turned on. Decreasing the amount of time between the core supply

power up and the I/O supply power up can minimize the effects of this current draw.

A dual power supply with simultaneous sequencing, such as available with

TPS563xx controllers or PT693x plug-in power modules, can be used to eliminate

the delay between core and I/O power up (see application note SLVA088,

Using the

TPS56300 to Power DSPs

supplies should power up to their respective regulation points quickly. The core and I/O supplies of

less. A power supply capable of providing several amps to an array of DSPs typically controls the

ramp-up rate to limit in-rush currents on start-up in order to reduce stress on transistors and filter

capacitors. Slow-start or soft-start mechanisms ramp the supply in 10 ms to 100 ms nominally to

preserve supply component reliability. Bringing the core and I/O supplies to their respective

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of the core and I/O supplies, since unknown factors such as the load currents drawn from each

supply during system shut down and the amount of capacitance present on each supply affect the

rate of decay. Active loads enabled during the power-down operation more predictably discharge

the core and I/O supply rails. The newest, DSP-specific, dual output LDO regulators and switching

power supply controllers from TI activate internal loads to discharge the output rails during power

down.

Of greater concern than timely power up and power down is system-level bus connection between