User's Manual

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7.1 Overview
7.2 PSC and PLLC Overview
Overview
In many applications, there may be specific requirements to minimize power consumption for both power
supply (or battery) and thermal considerations. There are two components to power consumption: active
power and leakage power. Active power is the power consumed to perform work and scales roughly with
clock frequency and the amount of computations being performed. Active power can be reduced by
controlling the clocks in such a way as to either operate at a clock setting just high enough to complete
the required operation in the required timeline or to run at a clock setting until the work is complete and
then drastically cut the clocks (that is, to PLL Bypass mode) until additional work must be performed.
Leakage power is due to static current leakage and occurs regardless of the clock rate. Leakage, or
standby power, is unavoidable while power is applied and scales roughly with the operating junction
temperatures. Leakage power can only be avoided by removing power completely from a device or
subsystem.
The TMS320DM643x DMP has several means of managing the power consumption, as detailed in the
following sections. There is extensive use of automatic clock gating in the design as well as
software-controlled module clock gating to not only reduce the clock tree power, but to also reduce
module power by basically freezing its state while not operating. Clock management enables you to slow
the clocks down on the chip in order to reduce switching power. In particular, the DM643x DMP includes
all of the power management features described in Table 7-1 .
Table 7-1. Power Management Features
Power Management Features Description
Clock Management
PLL power-down The PLLs can be powered-down when not in use to reduce switching power
Module clock ON/OFF Module clocks can be turned on/off to reduce switching power
Module clock frequency scaling Module clock frequency can be scaled to reduce switching power
DSP Sleep Management
DSP sleep modes The DSP can be put into sleep mode to reduce switching power
I/O Management
3.3 Volt I/O power-down The 3.3 V I/Os can be powered-down to reduce I/O cell power
DAC power-down The DAC's can be powered-down to reduce DAC power
The power and sleep controller (PSC) plays an important role in managing system power on/off, clock
on/off, and reset. Similarly, the PLL controller (PLLC) plays an important role in device clock generation.
The PSC and the PLLC are mentioned throughout this chapter. For detailed information on the PSC, see
Chapter 6 . For detailed information on the PLLC, see Chapter 4 and Chapter 5 .
Power Management78 SPRU978E – March 2008
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