MB90480/485 Series
• About the external impedance of the analog input and its sampling time
• A/D converter with sample and hold circuit. If the external impedance is too high to keep sufficient sampling
time, the analog voltage charged to the internal sample and hold capacitor is insufficient, adversely affecting
A/D conversion precision.
• Analog input equivalent circuit
R
Analog input
Comparator
C
During sampling : ON
R
C
MB90487B
MB90F481/F482
2.5 kΩ (Max) 31.0 pF (Max)
1.9 kΩ (Max) 25.0 pF (Max)
MB90F488B/F489B 1.9 kΩ (Max) 25.0 pF (Max)
Note: The values are reference values.
• To satisfy the A/D conversion precision standard, consider the relationship between the external impedance
and minimum sampling time and either adjust the register value and operating frequency or decrease the
external impedance so that the sampling time is longer than the minimum value.
• The relationship between external impedance and minimum sampling time
(External impedance = 0 kΩ to 100 kΩ)
(External impedance = 0 kΩ to 20 kΩ)
MB90F481/F482
MB90F488B/F489B
MB90F481/F482
MB90F488B/F489B
MB90487B
MB90487B
100
90
80
70
60
50
40
30
20
10
0
20
18
16
14
12
10
8
6
4
2
0
0
5
10
15
20
25
30
35
0
1
2
3
4
5
6
7
8
Minimum sampling time [µs]
Minimum sampling time [µs]
• If the sampling time cannot be sufficient, connect a capacitor of about 0.1 µF to the analog input pin.
• About errors
As |AVRH − AVSS| becomes smaller, values of relative errors grow larger.
Note : Concerning sampling time, and compare time when 3.6 V ≥ AVCC ≥ 2.7 V, then
Sampling time : 1.92 µs, compare time : 1.1 µs
Settings should ensure that actual values do not go below these values due to operating frequency changes.
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