MB95710M Series
MB95770M Series
Document Number: 002-09307 Rev. *D
Page 156 of 172
22.5.2 Notes on Using A/D Converter
• External impedance of analog input and its sampling time
The A/D converter of the MB95710M/770M Series has a sample and hold circuit. If the external impedance is too
high to keep sufficient sampling time, the analog voltage charged to the capacitor of the internal sample and hold
circuit is insufficient, adversely affecting A/D conversion precision. Therefore, to satisfy the A/D conversion precision
standard, considering the relationship between the external impedance and minimum sampling time, either adjust
the register value and operating frequency or decrease the external impedance so that the sampling time is longer
than the minimum value. In addition, if sufficient sampling time cannot be secured, connect a capacitor of about 0.1
µF to the analog input pin.
• Relationship between external impedance and minimum sampling time
The necessary sampling time varies according to external impedance. Ensure that the following conditions are ful-
filled when setting the sampling time.
T
s
: Sampling time
Rin : Input resistance of A/D converter
Cin : Input capacitance of A/D converter
Rext : Output impedance of external circuit
• A/D conversion error
As |V
CC
−
V
SS
| decreases, the A/D conversion error increases proportionately.
Note: The values are reference values.
4.5 V
≤
V
CC
≤
5.5 V
2.7 V
≤
V
CC
<
4.5 V
0.9 k
Ω
(max)
1.6 k
Ω
(max)
13 pF (max)
V
CC
Rin
Cin
13 pF (max)
1.8 V
≤
V
CC
<
2.7 V
4.0 k
Ω
(max)
13 pF (max)
Comparator
Analog input pins
(AN00 to AN07)
Analog signal source
Rin
Cin
Rext
• Analog input equivalent circuit
Ts
Rin Rext
+
(
)
Cin 9
×
×
≥