![](http://datasheet.mmic.net.cn/330000/MB90F549_datasheet_16437915/MB90F549_52.png)
MB90540/545 Series
52
(Continued)
7.
Notes on Using A/D Converter
Select the output impedance value for the external circuit of analog input according to the following conditions, :
Output impedance values of the external circuit of 15 k
or lower are recommended.
When capacitors are connected to external pins, the capacitance of several thousand times the internal
capacitor value is recommended to minimized the effect of voltage distribution between the external capacitor
and internal capacitor.
When the output impedance of the external circuit is too high, the sampling period for analog voltages may not
be sufficient (sampling period = 4.00
μ
s @machine clock of 16 MHz).
Error
The smaller the | AVRH
AVRL |, the greater the error would become relatively.
Linearity error
3FF
3FE
3FD
004
003
002
001
Analog input
AVRL
AVRH
Analog input
AVRL
AVRH
Actual conversion
characteristics
V
OT
(measured value)
V
(measured value)
Actual conversion
value
{1 LSB
×
(N – 1)+ V
OT
}
V
NT
Theoretical
characteristics
D
D
Differential linearity error
Theoretical characteristics
V
(measured value)
Actual conversion
value
V
NT
(measured value)
Actual conversion value
Linearity error of
digital output N
V
OT:
Voltage at transition of digital output from “000
H
” to “001
H
”
FST
: Voltage at transition of digital output from “3FE
H
” to “3FF
H
”
[LSB]
V
NT
– {1 LSB
×
(N – 1) + V
OT
}
1 LSB
V
(N + 1)T
– V
NT
1 LSB
=
[V]
V
FST
– V
OT
1022
=
1 LSB
– 1 LSB [LSB]
=
Differential linearity error
of digital N
N + 1
N
N – 1
N – 2
Equipment of analog input circuit model
Note: Listed values must be considered as standards.
Comparator
Analog input
C
0
C
1