MMCCMB2107 Freescale, MMCCMB2107 Datasheet - Page 486

• Manufacturer Part Number: MMCCMB2107
• Manufacturer: Freescale

Specifications of MMCCMB2107

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Queued Analog-to-Digital Converter (QADC)
18.11 Pin Connection Considerations
18.11.1 Analog Reference Pins
18.11.2 Analog Power Pins
Technical Data
486
The QADC requires accurate, noise-free input signals for proper
operation. This section discusses the design of external circuitry to
maximize QADC performance.
No A/D converter can be more accurate than its analog reference. Any
noise in the reference can result in at least that much error in a
conversion. The reference for the QADC, supplied by pins V
should be low-pass filtered from its source to obtain a noise-free, clean
signal. In many cases, simple capacitive bypassing may suffice. In
extreme cases, inductors or ferrite beads may be necessary if noise or
RF energy is present. Series resistance is not advisable since there is
an effective dc current requirement from the reference voltage by the
internal resistor string in the RC DAC array. External resistance may
introduce error in this architecture under certain conditions. Any series
devices in the filter network should contain a minimum amount of DC
resistance.
For accurate conversion results, the analog reference voltages must be
within the limits defined by V
subsection.
The analog supply pins (V
reference voltages (V
Figure 18-45
Since the sample amplifier is powered by V
accurately transfer input signal levels up to but not exceeding V
down to but not below V
the output from the sample amplifier is clipped.
In addition, V
V
than or equal to V
transferred the input signal, resolution is ratiometric within the limits
SSA
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. As long as V
Queued Analog-to-Digital Converter (QADC)
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RH
is a diagram of the analog input circuitry.
and V
SSA
RH
RH
RL
and the sample amplifier has accurately
is less than or equal to V
SSA
and V
must be within the range defined by V
DDA
. If the input signal is outside of this range,
DDA
and V
RL
) and of the analog multiplexer inputs.
and V
SSA
SSA
) define the limits of the analog
, as explained in this
DDA
DDA
and V
and V
MMC2107 – Rev. 2.0
SSA
, it can
RL
RH
is greater
MOTOROLA
and V
DDA
DDA
and
and
RL
,