28.6.1.1 Analog supply pins
Depending on the device, the analog power and ground supplies, V
DDA
and V
SSA
, of the
ADC module are available as:
• V
DDA
and V
SSA
available as separate pins—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.
• V
SSA
is shared on the same pin as the MCU digital V
SS
.
• 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.
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 must be the only ground connection
between these supplies, if possible. V
SSA
makes a good single point ground location.
28.6.1.2 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
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 are
selected using SC2[REFSEL]. The alternate voltage reference pair, V
ALTH
and V
ALTL
,
may select additional external pins or internal sources based on MCU configuration. See
the chip configuration information on the voltage references specific to this MCU.
In some packages, the external or alternate pairs are connected in the package to V
DDA
and V
SSA
, respectively. One of these positive references may be shared on the same pin
as V
DDA
on some devices. One of these ground references may be shared on the same pin
as V
SSA
on some devices.
If externally available, the positive reference may be connected to the same potential as
V
DDA
or may be driven by an external source to a level between the minimum Ref
Voltage High and the V
DDA
potential. The positive reference must never exceed V
DDA
. If
externally available, the ground reference must be connected to the same voltage
potential as V
SSA
. The voltage reference pairs must be routed carefully for maximum
noise immunity and bypass capacitors placed as near as possible to the package.
Application information
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
502 Freescale Semiconductor, Inc.
To Next Page
Loading...
