AN1740 Freescale Semiconductor / Motorola, AN1740 Datasheet - Page 47

• Manufacturer Part Number: AN1740
• Description: Applications Using the Analog Subsystem on MC68HC05JJ/JP Series Microcontrollers
• Manufacturer: Freescale Semiconductor / Motorola

Performance
Calculations
AN1740
MOTOROLA
On the other hand, single slope A/D convertors have some
disadvantages:
Overall, the single slope A/D is well suited to many applications with
slow-moving signals (<1000 Hz) which are common with many analog
sensors and for user input sources like potentiometers. The additional
software is offset by the smaller size of the single slope A/D circuitry. The
single-slope A/D support circuitry on the MC68HC05JJ/JP series of
MCUs uses about 20% less silicon area than the 8-bit SAR A/D
commonly found on the MC68HC05P series; and this 20% reduction is
equivalent in silicon area to about 400 bytes of ROM. Therefore, even
with extensive software, the single slope A/D implementation will use
less silicon area than a typical SAR A/D design.
Fundamental to the single slope A/D conversion technique is the
equation relating time to voltage dependent on the external ramping
capacitor and its charging current:
where:
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Freescale Semiconductor, Inc.
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For More Information On This Product,
Slow conversion times, in the milliseconds
More software required to do the actual conversion
External ramp capacitor needed
= Charge time (seconds)
= Voltage to reach (volts)
= External ramp capacitor ( F)
= Charge current ( A)
=
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Analog-to-Digital Conversion
Application Note
47