
Analog Integrated Circuit Device Data
Freescale Semiconductor
57
PC34708
Functional Block Requirements and Behaviors
Buck Switchers Block Description and Application Information
7.2.9.2
Standby Delay
A provision to delay the Standby response is included. This allows the processor and peripherals, some time after a Standby
instruction has been received, to terminate processes to facilitate seamless Standby exiting and re-entrance into Normal
operating mode.
A programmable delay is provided to hold off the system response to a Standby event. When enabled (STBYDLY = 01, 10, or
11), STBYDLY will delay the STANDBY initiated response for the entire IC until the STBYDLY counter expires.
Note that this delay is applied only when going into Standby, and no delay is applied when coming out of Standby. Also, an
allowance should be accounted for synchronization of the asynchronous Standby event and the internal clocking edges (up to a
full 32 k cycle of additional delay).
7.3
Buck Switchers Block Description and Application Information
7.3.1
Buck Switchers General Control
Operational modes of the Buck switchers can be controlled by direct SPI programming, altered by the state of the STANDBY pin,
by direct state machine influence (i.e., entering Off or low power Off states, for example), or by load current magnitude when so
configured (Auto Pulse skip mode). Available modes include PWM with No Pulse Skipping (PWM), PWM with Pulse Skipping
(PWMPS), Pulse Frequency Mode (PFM), Automatic Pulse Skip (APS), and Off. The transition between the two modes PWMPS
and PWM can occur automatically, based on the load current (auto pulse skip mode). For light loading, the switchers should be
put into PFM mode to optimize efficiency.
SW1A/B, SW2, SW3, SW4A/B, and SW5, can be configured for mode switching with STANDBY or autonomously, based on load
current Auto pulse skip mode. Additionally, provisions are made for maintaining PFM operation in User off and Memhold modes,
to support state retention for faster startup from the Low Power Off modes for Warm Start or Warm Boot. SWxMODE[3:0] bits
will be reset to their default values defined by PUMSx settings by the startup sequencer.
Table 53 summarizes the Buck switcher programmability for Normal and Standby modes.
Table 52. Delay of STANDBY- Initiated Response
STBYDLY[1:0]
Function
00
No Delay
01
One 32 k period (default)
10
Two 32 k periods
11
Three 32 k periods
Table 53. Switcher Mode Control for Normal and Standby Operation
SWxMODE[3:0]
Normal Mode
Standby Mode
0000
Off
0001
PWM
Off
0010
PWMPS
Off
0011
PFM
Off
0100
APS
Off
0101
PWM
0110
PWM
APS
0111
Off
1000
APS
1001
PWM
PWMPS
1010
PWMPS