Information

31.6 Application information
This section contains information for using the ADC module in applications. The ADC
has been designed to be integrated into a microcontroller for use in embedded control
applications requiring an ADC.
31.6.1 External pins and routing
The following sections discuss the external pins associated with the ADC module and
how they should be used for best results.
31.6.1.1 Analog supply pins
The ADC module has analog power and ground supplies (V
DDA
and V
SSA
) available as
separate pins on some devices. V
SSA
is shared on the same pin as the MCU digital VSS
on some devices. On other devices, V
SSA
and V
DDA
are shared with the MCU digital
supply pins. In these cases, there are separate pads for the analog supplies bonded to the
same pin as the corresponding digital supply so that some degree of isolation between the
supplies is maintained.
When available on a separate pin, both V
DDA
and V
SSA
must be connected to the same
voltage potential as their corresponding MCU digital supply (V
DD
and V
SS
) and must be
routed carefully for maximum noise immunity and bypass capacitors placed as near as
possible to the package.
If separate power supplies are used for analog and digital power, the ground connection
between these supplies must be at the V
SSA
pin. This should be the only ground
connection between these supplies if possible. The V
SSA
pin makes a good single point
ground location.
31.6.1.2 Analog voltage reference pins
In addition to the analog supplies, the ADC module has connections for two reference
voltage inputs used by the converter, V
REFSH
and V
REFSL
. V
REFSH
is the high reference
voltage for the converter. V
REFSL
is the low reference voltage for the converter.
The ADC can be configured to accept one of two voltage reference pairs for V
REFSH
and
V
REFSL
. Each pair contains a positive reference and a ground reference. The two pairs are
external (V
REFH
and V
REFL
) and alternate (V
ALTH
and V
ALTL
). These voltage references
Application information
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
626 Freescale Semiconductor, Inc.