33
MB89920 Series
5. A/D Converter Electrical Characteristics
(AV
CC
= V
CC
= +3.5 V to +6.0 V, F
C
= 8 MH
Z
, AV
SS
= V
SS
= 0.0 V, T
A
= –40
°
C to +85
°
C)
Precautions: The smaller | AVR – AV
SS
|, the greater the error would become relatively.
The output impedance of the external circuit for the analog input must satisfy the following conditions:
Output impedance of the external circuit < Approx. 10 k
If the output impedance of the external circuit is too high, an analog voltage sampling time might be
insufficient (sampling time = 7.5
μ
s at 8 MHz oscillation).
An analog input equivalent circuit is shown below.
Since the A/D converter contains sample hold circuit, the level of the analog input pin might not stabilize within the
sampling period after A/D activation, resulting in inaccurate A/D conversion values, if the input impedance to the
analog pin is too high. Be sure to maintain an appropriate input impedance to the analog pin.
It is recommended to keep the input impedance to the analog pin not exceed 10 k
. If it exceeds 10 k
, it is
recommended to connect a capacitor of about 0.1
μ
F for the analog input pin.
Except for the sampling period after A/D activation, the input leakage current of the analog input pin is less than 10
μ
A.
Parameter
Sym-
bol
Pin
Condition
Value
Unit
Min.
Typ.
Max.
Resolution
—
—
AV
CC
= AVR =
V
CC
—
—
10
±
2.0
±
1.5
±
3.0
bit
Linearity error
—
—
LSB
Differential linearity error
—
—
LSB
Differential total error
—
—
LSB
Zero transition voltage V
OT
AN0 to AN7
AV
SS
– 1.5 LSB
AV
SS
+ 0.5 LSB
AV
SS
+ 2.5 LSB
mV
Full-scale transition
voltage
V
FST
AN0 to AN7
AVR – 3.5 LSB
AVR – 1.5 LSB
AVR + 0.5 LSB
mV
Interchannel disparity
—
—
—
—
4
LSB
μ
s
μ
A
V
A/D mode conversion time
—
—
16.5
Analog port input current
V
AIN
AN0 to AN7
At 8-MH
Z
oscillattion
—
—
10
Analog input voltage
—
AN0 to AN7
0.0
—
AVR
Reference voltage
AVR
0.0
—
AV
CC
V
Reference voltage
supply current
I
R
AVR
AVR = 5.0 V
—
200
μ
A
Comparator
C ..
R ..
(
Sample hold circuit
Close for approx. 15 instruction cycles
after activating A/D conversion.
Analog channel selector
R
≤
10 k
is
recommended.
AN
If R > 10 k
, it is recommended
to connect an external capacitor
of approx. 0.1
μ
F.
Microcontroller’s internal circuit