Datasheet

FUNCTIONAL DEVICE OPERATION
OPERATING MODES
Analog Integrated Circuit Device Data
66 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
0 X X Off
1 0 X On
1 1 0 On
1 1 1 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 Off
0001 PWM Off
0010 PWMPS Off
0011 PFM Off
0100 Auto Off
0101 PWM PWM
0110 PWM Auto
0111 NA NA
1000 Auto Auto
1001 PWM PWMPS
1010 PWMPS PWMPS
1011 PWMPS Auto
1100 Auto PFM
1101 PWM PFM
1110 PWMPS PFM
1111 PFM PFM
Notes
63. STANDBY defined as logical AND of STANDBY and STANDBYSEC pin