13892 datasheet(66/158 Pages) FREESCALE

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FUNCTIONAL DEVICE OPERATION

OPERATING MODES

Analog Integrated Circuit Device Data



Freescale Semiconductor

MC13892

BUCK REGULATORS

Operational modes of the Buck regulators can be controlled by direct SPI programming, altered by the state of the STANDBY

pins, by direct state machine influence, or by load current magnitude when so configured. Available modes include PWM with

No Pulse Skipping (PWM), PWM with Pulse Skipping (PWMPS), Pulse Frequency Mode (PFM), and Off. The transition between

the two modes PWMPS and PFM can occur automatically, based on the load current. Therefore, no specific control is required

to put the switchers in a Low-power mode. When the buck regulators are not configured in the Auto mode, power savings may

be achieved by disabling switchers when not needed, or running them in PFM mode if loading conditions are light enough.

SW1, SW2, SW3, and SW4 can be configured for mode switching with STANDBY or autonomously based on load current with

adaptive mode control (Auto). Additionally, provisions are made for maintaining PFM operation in USEROFF and MEMHOLD

modes to support state retention for faster startup from the Low-power Off modes for Warm Start or Warm Boot.

Table 34 summarizes the Buck regulator programmability for Normal and Standby modes.

In addition to controlling the operating mode in Standby, the voltage setting can be changed. The transition in voltage is

handled in a controlled slope manner, see Supplies, for details. Each switcher has an associated set of SPI bits for Standby mode

set points. By default the Standby settings are identical to the non-Standby settings, which are initially defined by PUMS

programming.

The actual operating mode of the switchers as a function of STANDBY pins is not reflected through the SPI. The SPI will read

back what is programmed in SWxMODE[3:0], not the actual state that may be altered as described previously.

Table 35 and Table 36 show the switcher mode control in the Low-power Off states. Note that a Low-power Off activated SWx

should use the Standby set point as programmed by SWxSTBY[4:0]. The activated switcher(s) will maintain settings for mode

and voltage until the next startup event. When the respective time slot of the startup sequencer is reached for a given switcher,

its mode and voltage settings will be updated the same as if starting out of the Off state (except that switchers active through a

Low-power Off mode will not be off when the startup sequencer is started).

Table 33. LDO Regulator Control (Internal Pass Device LDOs)

VxEN

VxSTBY

STANDBY

Regulator Vx

Off

Notes

61.

This table is valid for regulators with an internal pass device

62.

STANDBY refers to a Standby event as described earlier

Table 34. Switcher Mode Control for Normal and Standby Operation

SWxMODE[3:0]

Normal mode(63)

Standby Mode(63)

0000

Off

0001

PWM

Off

0010

PWMPS

Off

0011

PFM

Off

0100

Auto

Off

0101

PWM

0110

PWM

Auto

0111

1000

Auto

1001

PWM

PWMPS

1010

PWMPS

1011

PWMPS

Auto

1100

Auto

PFM

1101

PWM

PFM

1110

PWMPS

PFM

1111

PFM

Notes

63.

STANDBY defined as logical AND of STANDBY and STANDBYSEC pin

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