Datasheet

Analog Integrated Circuit Device Data
Freescale Semiconductor 66
MC34708
Functional Block Description
7.5.6.2 LDO Regulator Control
The regulators with embedded pass devices (VPLL, VGEN1, and VUSB) have an adaptive biasing scheme thus, there are no
distinct operating modes such as a Normal mode and a Low Power mode. Therefore, no specific control is required to put these
regulators in a Low Power mode.
The external pass regulator (VDAC) can also operate in a normal and low power mode. However, since a load current detection
cannot be performed for this regulator, the transition between both modes is not automatic and is controlled by setting the
corresponding mode bits for the operational behavior desired.
The regulators VUSB2, and VGEN2 can be configured for using the internal pass device or external pass device as explained in
Supplies. For both configurations, the transition between both modes is controlled by setting the VxMODE bit for the specific
regulator. Therefore, depending on the configuration selected, the automatic Low Power mode determines availability.
The regulators can be disabled and the general purpose outputs can be forced low when going into Standby (note that the
Standby response timing can be altered with the STBYDLY function, as described in the previous section). Each regulator has
an associated SPI bit for this. When the bit is not set, STANDBY is of no influence. The actual operating mode of the regulators
as a function of STANDBY is not reflected through SPI. In other words, the SPI will read back what is programmed, not the actual
state.
For regulators with internal pass devices, the previous table can be simplified by elimination of the VxMODE column.
7.5.6.3 Transient Response Waveforms
The transient load and line response are specified with the waveforms as depicted in Figure 18. Note that where the transient
load response refers to the overshoot only, so excluding the DC shift itself, the transient line response refers to the sum of both
overshoot and DC shift. This is also valid for the mode transition response.
Table 54. LDO Regulator Control (external pass device LDOs)
VxEN VxMODE VxSTBY STANDBY
(58)
Regulator Vx
0 X X X Off
1 0 0 X On
1 1 0 X Low Power
1 X 1 0 On
1 0 1 1 Off
1 1 1 1 Low Power
Notes
58. STANDBY refers to a Standby event as described earlier
Table 55. LDO Regulator Control (internal pass device LDOs)
VxEN VxSTBY STANDBY
(59)
Regulator Vx
0 X X Off
1 0 X On
1 1 0 On
1 1 1 Off
Notes
59. STANDBY refers to a Standby event as described earlier