PXD20RM Datasheet, PDF (1573/1628 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

Chapter 48
Voltage Regulators and Power Supplies
48.1 Introduction
This device includes three on-chip voltage regulators for power management and distribution, allowing
low-power operation and optimization of power consumption.
On this device, the general purpose inputs and outputs (GPIO) are arranged in several banks with separate
external GPIO power supply pins, allowing groups of GPIO to operate at different supply voltages.
48.2 Power-up sequencing
The preferred power-up sequence for PXD20 is as follows:
1. Generic IO supplies or noise-free supplies, consisting of:
— VDDA
— VDDE_A
— VDDE_B
— VDDM
— VDD_DR
— VDD33_DR
— VDDPLL
2. All 3.3V supplies (VDDE_B & VDD33_DR) should be ramped up first, and then the rest of the
I/O supplies should be ramped up (VDDA, VDDE_A, VDDM, VDD_DR).
3. VDDR, the regulator input supply, should be the last supply to ramp up; all supplies can be ramped
up together as long as VDDR is included. So all 5V supplies should be ramped up after the 3.3V
supplies, and if all the supplies are of the same level, they can be ramped up together as well.
4. LV supply (VDD12). If Vreg is in bypass mode and the core supply (1.2V) is supplied externally,
then this should be the last supply given.
NOTE
For DDR, the 3.3 V supply (VDD33_DR) should come before VDD_DR.
This sequence ensures that when VREG releases its LVDs, the IO and other HV segments are powered
properly. This is important because PXD20 doesn't monitor LVDs on IO HV supplies.
48.3 Voltage regulators
The internal voltage regulators are used to provide a 1.2 V digital supply to the internal logic of the device.
The main/input supply is 3.3 V to 5.0 V ± 10% and the digital/regulated output supply is 1.2 V ± 10%. The
voltage regulator used in this device comprises three regulators.
• High power or main regulator (HPREG) requiring an external NPN ballast transistor.
• Low power regulator (LPREG)
Freescale Semiconductor
PXD20 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
48-1