MMC2114 MOTOROLA [Motorola, Inc], MMC2114 Datasheet - Page 476

• Manufacturer Part Number: MMC2114
• Description: M CORE Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

Queued Analog-to-Digital Converter (QADC)
19.9.3.3 Channel Decode and Multiplexer
19.9.3.4 Sample Buffer
19.9.3.5 Digital-to-Analog Converter (DAC) Array
Advance Information
476
NOTE:
Because of internal RC time constants, use of a two QCLK sample time
in bypass mode will cause serious errors when operating the QADC at
high frequencies.
The internal multiplexer selects one of the eight analog input pins for
conversion. The selected input is connected to the sample buffer
amplifier or to the sample capacitor. The multiplexer also includes
positive and negative stress protection circuitry, which prevents
deselected channels from affecting the selected channel when current is
injected into the deselected channels.
The sample buffer is used to raise the effective input impedance of the
A/D converter, so that external factors (higher bandwidth or higher
impedance) are less critical to accuracy. The input voltage is buffered
onto the sample capacitor to reduce crosstalk between channels.
The digital-to-analog converter (DAC) array consists of binary-weighted
capacitors and a resistor-divider chain. The reference voltages, V
V
also converts the following three internal channels:
QCLK
RL
•
•
•
Freescale Semiconductor, Inc.
, are used by the DAC to perform ratiometric conversions. The DAC
For More Information On This Product,
Queued Analog-to-Digital Converter (QADC)
V
V
(V
RH
RL
RH
SAMPLE TIME
N CYCLES
(2,4,8,16)
SAMPLE
Figure 19-21. Bypass Mode Conversion Timing
— reference voltage low
— reference voltage high
–V
TIME:
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RL
)/2 — reference voltage
SUCCESSIVE APPROXIMATION RESOLUTION SEQUENCE
MMC2114 • MMC2113 • MMC2112 — Rev. 1.0
RESOLUTION
10 CYCLES
TIME:
MOTOROLA
RH
and