
Analog Integrated Circuit Device Data
Freescale Semiconductor
74
PC34708
Functional Block Requirements and Behaviors
Buck Switchers Block Description and Application Information
7.3.3
Dynamic Voltage Scaling
To reduce overall power consumption, processor core voltages can be varied depending on the mode or activity level of the
processor. SW1A/B and SW2 allow for two different set points with controlled transitions to avoid sudden output voltage changes,
which could cause logic disruptions on their loads.
Preset operating points for SW1A/B and SW2 can be set up for:
Normal operation: output value selected by SPI bits SWx[5:0]. Voltage transitions initiated by SPI writes to SWx[5:0] are
governed by the DVS stepping rate shown in the following tables.
Standby (Deep Sleep): can be higher or lower than normal operation, but is typically selected to be the lowest state retention
voltage of a given process. Set by SPI bits SWxSTBY[5:0] and controlled by a Standby event. Voltage transitions initiated by
Standby are governed by the SWxDVSSPEED[1:0] SPI bits shown in
Table 71.The following table summarizes the set point control and DVS time stepping applied to SW1A/B and SW2.
tON-SW5
Turn-on Time
Enable to 90% of end value IL = 0
-
500
s
fSW5
Switching Frequency
PLLX = 0
PLLX = 1
-
2.0
4.0
-
MHz
ISW5Q
Quiescent Current Consumption
PWM MODE, IL = 0 mA; device not switching
PFM MODE, IL = 0 mA; device not switching
-
50
15
-
A
Efficiency
PFM, 1.80 V, 1.0 mA
PWM Pulse skipping, 1.80 V, 50 mA
PWM Pulse skipping, 1.80 V, 500 mA
PWM, 1.80 V, 1000 mA
-
%
Notes
57.
Transient Loading for load Steps of ILMAX/2
58.
Efficiency numbers at VIN=3.6V, Excludes the quiescent current.
Table 71. DVS Control Logic Table for SW1A/B and SW2
STANDBY
Set Point Selected by
0
SWx[4:0]
1
SWxSTBY[4:0]
Table 72. DVS Speed Selection
SWxDVSSPEED[1:0]
Function
00
12.5 mV step each 2.0
μs
01 (default)
12.5 mV step each 4.0
μs
10
12.5 mV step each 8.0
μs
11
12.5 mV step each 16.0
μs
Table 70. SW5 Electrical Specifications
Characteristics noted under conditions BP = 3.6 V, VBUS = 5.0 V, -40°C ≤ TA ≤ 85°C, unless otherwise noted. Typical values at
BP = 3.6 V and TA = 25°C under nominal conditions, unless otherwise noted.
Symbol
Characteristic
Min
Typ
Max
Unit
Notes