mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 671

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

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
voltage potential as their corresponding MCU digital supply (V
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
connection between these supplies if possible. The V
ground location.
29.6.1.2 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
voltage for the converter. V
The ADC can be configured to accept one of two voltage reference pairs for V
V
external (V
are selected using the REFSEL bits in the SC2 register. The alternate (V
voltage reference pair may select additional external pins or internal sources depending
on MCU configuration. Refer to 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
and V
as V
as V
If externally available, the positive reference may be connected to the same potential as
V
Voltage High and the V
externally available, the ground reference must be connected to the same voltage
potential as V
noise immunity and bypass capacitors placed as near as possible to the package.
AC current in the form of current spikes required to supply charge to the capacitor array
at each successive approximation step is drawn through the V
best external component to meet this current demand is a 0.1 μF capacitor with good high
Freescale Semiconductor, Inc.
REFSL
DDA
DDA
SSA
SSA
or may be driven by an external source to a level between the minimum Ref
. Each pair contains a positive reference and a ground reference. The two pairs are
on some devices.
on some devices. One of these ground references may be shared on the same pin
, respectively. One of these positive references may be shared on the same pin
REFH
SSA
and V
. The voltage reference pairs must be routed carefully for maximum
REFL
DDA
MCF51JF128 Reference Manual, Rev. 2, 03/2011
) and alternate (V
REFSL
potential (the positive reference must never exceed V
is the low reference voltage for the converter.
REFSH
SSA
Preliminary
DDA
pin. This should be the only ground
ALTH
and V
and V
and V
REFSL
SSA
SSA
Chapter 29 Analog-to-Digital Converter (ADC)
must be connected to the same
ALTL
pin makes a good single point
. V
REFSH
). These voltage references
REFH
DD
and V
is the high reference
and V
ALTH
SS
REFL
) and must be
and V
loop. The
REFSH
DDA
DDA
ALTL
and
). If
671
)