AN2727 Freescale Semiconductor / Motorola, AN2727 Datasheet - Page 9

• Manufacturer Part Number: AN2727
• Description: Designing Hardware for the HCS12 D-Family
• Manufacturer: Freescale Semiconductor / Motorola

In extreme cases, where high frequency system noise is present, low ESR
beads may be necessary on VRH. Series resistance should be avoided, as each ATD reference draws
~375 µA from the reference supply (VRH=5V).
Ground
The oscillator return should be directly to VSSPLL, which should in turn be connected to all other digital
grounds via a low impedance ground plane (preferred) or a ‘star’ configuration centred at VSSR.
The oscillator ground should not be otherwise connected to the digital ground.
Vssa, Vssr
Where ATD accuracy is important, these should star separately from the external voltage regulator or
voltage source.
1. Equivalent series resistance.
Freescale Semiconductor
GND
VIN
Star connection point for other
digital MCU ground pins
Designing Hardware for the HCS12 D-Family, Rev. 0
Regulator
External
Voltage
VSS
VDD
100nF
VDDA
VDDR
VSSR
VSSA
Reference
VRH
VRL
Internal
Module
Analog
Vreg
ATD
1
series inductors and/or ferrite
VSS1/2
MCU
logic
ATD
I/O
HCS12 Power Supplies
9