Chapter 17 Voltage Regulator (S12VREG3V3V5)
MC9S12XDP512 Data Sheet, Rev. 2.11
Freescale Semiconductor 737
17.2 External Signal Description
Due to the nature of VREG_3V3 being a voltage regulator providing the chip internal power supply
voltages, most signals are power supply signals connected to pads.
Table 17-1 shows all signals of VREG_3V3 associated with pins.
NOTE
Check device level specification for connectivity of the signals.

17.2.1 VDDR — Regulator Power Input Pins

Signal VDDR is the power input of VREG_3V3. All currents sourced into the regulator loads flow through
this pin. A chip external decoupling capacitor (100 nF...220 nF, X7R ceramic) between VDDR and VSSR
(if VSSR is not available VSS) can smooth ripple on VDDR.
For entering Shutdown Mode, pin VDDR should also be tied to ground on devices without VREGEN pin.

17.2.2 VDDA, VSSA — Regulator Reference Supply Pins

Signals VDDA/VSSA, which are supposed to be relatively quiet, are used to supply the analog parts of the
regulator. Internal precision reference circuits are supplied from these signals. A chip external decoupling
capacitor (100 nF...220 nF, X7R ceramic) between VDDA and VSSA can further improve the quality of this
supply.

17.2.3 VDD, VSS — Regulator Output1 (Core Logic) Pins

Signals VDD/VSS are the primary outputs of VREG_3V3 that provide the power supply for the core logic.
These signals are connected to device pins to allow external decoupling capacitors (100 nF...220 nF, X7R
ceramic).
In Shutdown Mode an external supply driving VDD/VSS can replace the voltage regulator.
Table 17-1. Signal Properties
Name Function Reset State Pull Up
VDDR Power input (positive supply)
VDDA Quiet input (positive supply)
VSSA Quiet input (ground)
VDD Primary output (positive supply)
VSS Primary output (ground)
VDDPLL Secondary output (positive supply)
VSSPLL Secondary output (ground)
VREGEN (optional) Optional Regulator Enable