Renesas M32R/ECU Series, User Manual

Page: 486 / 839

11
11-41
A-D Converters
32180 Group User's Manual (Rev.1.0)
11.4 Inflow Current Bypass Circuit
11.4 Inflow Current Bypass Circuit
If when the A-D Converter is A-D converting a selected analog input an overvoltage exceeding the converter’s
absolute maximum rating is applied to any unselected analog input, the selector for the unselected analog input is
inadvertently turned on by that overvoltage. This causes current to wrap around to the selected analog input, and
the accuracy of the A-D conversion result is thereby deteriorated.
The Inflow Current Bypass Circuit fixes the internal signals of unselected analog inputs to the GND level, so that
when an overvoltage is applied, this circuit lets the current flow into the GND and prevents it from wrapping around
to the selected analog input. That way, the accuracy of the A-D conversion result is prevented from being deterio-
rated by extreme voltages.
This circuit is always active while the A-D Converter is operating, and does not need to be controlled in software.
Unselected
channel
Selected
channel
To the internal logic
of the A-D Converter
OFF
ON
OFF
ON
ON
OFF
Fixed to GND level
External input
latched into
Assist circuit
Figure 11.4.1 Configuration of the Inflow Current Bypass Circuit
Figure 11.4.2 Example of an Inflow Current Bypass Circuit where VCCE + 0.7 V or More is Applied
Unselected channel
Selected channel
To the internal logic
of the A-D Converter
OFF
ON
OFF
ON
ON
OFF
Assist circuit
VCCE + 0.7 V or more
Leakage current
generated
Sensor input
Leakage current
generated
Unaffected
by leakage