Advertisement
ADCC.2:
ADC Overload Current
During exceptional conditions in the application system an overload current I
inputs of the A/D converter when V
specified in the Data Sheet:
= | ±5 mA |
I
OVmax
The specified total unadjusted error TUE
occur on maximum 2 not selected analog input pins and the absolute sum of input overload currents
on all analog input pins does not exceed 10 mA.
Due to an internal problem, the specified TUE value is only met for a positive overload current 0 mA ≤
≤ +5 mA (all currents flowing into the microcontroller are defined as positive and all currents flowing
I
OV
out of it are defined as negative).
If the exceptional conditions in the application system cause a negative overload current, then the
maximum TUE can be significantly exceeded (depending on value of I
channel):
Problem Description in Detail:
1. Overload Current at analog Channel AN0 - AN9 and AN11 - AN15
If a negative overload current I
current I
(crosstalk current) is caused at the neighbour channels ANn-1 and ANn+1. This behavior
AN
causes an additional unadjusted error AUE to the ADC result.
Relation between I
2. Overload Current at digital Channel P7.7
A negative overload current I
input AN0. The relation between both channels is also defined by ovf1:
3. Overload Current at analog Channel AN10
The behavior of an overload current at analog channel AN10 is different to all others because it has
an influence to V
AGND
and analog ground of the system, the crosstalk current can cause an additional unadjusted error
AUE to all other analog channels.
In case R
< 40 Ohm the possible additional error to all other channels is smaler than 0.5 LSB
AGND
with the condition of I
In case R
> 40 Ohm the AUE has to be calculated via:
AGND
5. Values of ovf1 and ovf2
Parameter
Overload factor_1
Overload factor_2
Semiconductor Group
> V
or V
AIN
dd
max
occurs on analog input channel ANn (n≠10) than an additional
OV
and I
:
AN
OV
I
= ovf1 * I
ANn+1
I
= ovf1 * I
ANn-1
at digital Port P7.7 causes an additional current I
OV
I
= ovf1 * I
AN0
. Depending on R
AGND
= - 5 mA at AN10. In that case the relation between AN10 and AN11 is:
OVmax
I
= ovf1 * I
AN11
I
= ovf2 * I
ANGND
Symbol
ovf1
ovf2
Errata Sheet, C167CR-LM, ES-DB, DB, 1.1, Mh
< V
. For this case, the following conditions are
AIN
ss
= | ±2 LSB | is only guaranteed if overload conditions
(n≠10)
OVn
(n≠10)
OVn
OVP7.7
, the resistance between V
OV10
OV10
Min
- 0.0047
- 0.0094
can occur on the analog
OV
and R
of converted
OV
AIN
at the analog
AN
pin of the microcontroller
AGND
(R
< 40 Ohm)
AGND
(R
> 40 Ohm)
AGND
Max
0
0
- 8 of 11 -
Advertisement
