MagnaChip HMS39C7092, User Manual, Page: 181 / 197

Flash MCU(HMS39C7092) A/D Converter
181
13.5 Usage Notes
When using the A/D converter, note the following points:
1. Analog Input Voltage Range: During A/D conversion, the voltages input to the
analog input pins AN
n
should be in the range AV
ss
≤
AN
n
≤
V
REF
.
2. Relationships of AV
CC
and AV
SS
to V
CC
and V
SS
: AV
CC
, AV
SS
, V
CC
, and V
SS
should
be related as follows: AV
SS
= V
SS
. AV
CC
and AV
SS
must not be left open, even if the
A/D converter is not used.
3. V
REF
Programming Range: The reference voltage input at the V
REF
pin should be in
the range V
REF
≤
AV
CC
.
Note on Board Design: In board layout, separate the digital circuits from the analog
circuits as much as possible. Particularly avoid layouts in which the signal lines of
digital circuits cross or closely approach the signal lines of analog circuits. Induction
and other effects may cause the analog circuits to operate incorrectly, or may
adversely affect the accuracy of A/D conversion. The analog input signals (AN
0
to
AN
4
), analog reference voltage (V
REF
), and analog supply voltage (AV
CC
) must be
separated from digital circuit by the analog ground (AV
SS
). The analog ground (AV
SS
)
should be connected to a stable digital ground (V
SS
) at one point on the board.
Note on Noise: To prevent damage from surges and other abnormal voltages at the
analog input pins (AN
0
to AN
4
) and analog reference voltage pin (V
REF
), connect a
protection circuit like the one in Figure 13.3 between AV
CC
and AV
SS
. The bypass
capacitors connected to AV
CC
and V
REF
and the filter capacitors connected to AN
0
to
AN
4
must be connected to AV
SS
.
4. A/D Conversion Accuracy Definitions: A/D conversion accuracy in the
HMS39C7092 is defined as follows:
•
Resolution: Digital output code length of A/D converter
•
Offset error: Deviation from ideal A/D conversion characteristic of analog
input voltage required to raise digital output from minimum
voltage value 0000000000 to 0000000001 (figure 13.4)
•
Full-scale error: Deviation from ideal A.D conversion characteristic of analog
input voltage required to raise digital output from 1111111110
to 1111111111 (figure 13.4)
•
Quantization error: Intrinsic error of the A/D converter;1/2 LSB (figure 13.5)
•
Nonlinearity error: Deviation from ideal A/D conversion characteristic in range
from zero volts to full scale, exclusive of offset error, full-
scale error, and quantization error.
•
Absolute accuracy: Deviation of digital value from analog input value, including
offset error, full-scale error, quantization error, and
nonlinearity error.