Datasheet

Table Of Contents
Voltage Regulator (VREG)
MC9S12DP256 — Revision 1.1
Voltage Regulator (VREG)
Reset Initialization
On system power up, the voltage regulator is started in run mode if
VREGEN is connected to VDDA. VDDA must be monitored by an
external voltage comparator to ensure that the MCU is not executing
code while the power supply is out of specification limits to avoid
erroneous operation.
Modes of Operation
The voltage regulator has three operating modes: run, standby and
disabled.
Normal Operation:
Run
In run mode, both regulating loops of the voltage regulator are active.
This mode is selected whenever the CPU is neither in stop nor in pseudo
stop mode and VREGEN is externally connected to VDDA.
Special Operation:
Standby
Standby mode is selected when the CPU is in stop or pseudo stop mode
and VREGEN is externally connected to VDDA. In standby mode, the
gates of the power transistors are directly connected to the reference
voltage V
REF
((VDDA - VSSA)/2), the loop amplifiers are switched off. In
this case, the voltage regulator acts as a voltage clamp. In standby
mode, the source resistance of the regulator is increased, but power
consumption is significantly decreased.
Special Operation:
Disabled
Shutdown mode can be selected by connecting VREGEN to VSSA. In
this case, VDD and VDDPLL (2.5V±10%) must be supplied externally. In
shutdown mode, VREG will also generate the power on reset signal.
Freescale Semiconductor, I
Freescale Semiconductor, Inc.
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