13892 datasheet(79/161 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

13892

FUNCTIONAL DEVICE OPERATION

SUPPLIES

Since the switchers have a strong sourcing capability but no active sinking capability, the rising slope is determined by the

switcher, but the falling slope can be influenced by the load. Additionally, as the current capability in PFM mode is reduced,

controlled DVS transitions in PFM mode could be affected. Critically timed DVS transitions are best assured with PWM mode

operation.

Note that there is a special mode of DVS control for Switcher Increment / Decrement (SID) operation described later in this

chapter.

DVS pin controls are not included for SW3 and SW4. However, voltage transitions programmed through the SPI will step in

increments of 25 mV per 4.0

μs, to allow SPI controlled voltage stepping with SWx[4:0]. Additionally, SW3 and SW4 include

Standby mode set point programmability.

Figure 20 shows the general behavior for the switchers when initiated with pin controlled DVS, SPI programming or standby

control.

Figure 20. SW1 Voltage Stepping with Pin Controlled DVS

Note that the DVSx input pins are reconfigured for Switcher Increment / Decrement (SID) control mode when SPI bit

SIDEN = 1. Refer to the SID description below for further details.

SWITCHER INCREMENT / DECREMENT

A scheme for incrementing or decrementing the operating set points of SW1 and SW2 is desirable for improved Dynamic

Process and Temperature Compensation (DPTC) control in support of fine tuning power domains for the processor supply tree.

An increment command will increase the set point voltage by a single 25 mV step. A decrement command will decrease the set

point by a single 25 mV step. The transition time for the step will be the same as programmed with SWxDVSSPEED[1:0] for DVS

stepping. If a switcher runs out of programmable range (in either direction), as constrained by programmable stops, then the

increment or decrement command shall be ignored.

The Switcher Increment / Decrement (SID) function is enabled with SIDEN = 1. This will reassign the function of the DVS1 and

DVS2 pins, from the default toggling between Normal and DVS operating modes, to a jog control mode for the switcher which

DVSx is assigned. Once enabled, the switcher being controlled will start at the Normal mode set point as programmed with

SWx[4:0] and await any jog commands from the processor. The adjustment scheme essentially intercepts the Normal mode set

point SPI bits (i.e., but not DVS or Standby programmed set points), and makes any necessary adjustments based on jog up or

jog down commands. The modified set point bits are then immediately passed to the switching regulator, which would then do a

DVS step in the appropriate direction. The SPI bits containing Normal mode programming are not directly altered.

Table 50. DVS Speed Selection for SW1 and SW2

SWxDVSSPEED[1:0]

Function

25 mV step each 2.0

μs

01 (default)

25 mV step each 4.0

μs

25 mV step each 8.0

μs

25 mV step each 16

μs

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