Advertisement
6. Effects on the Conversion Result and TUE
The effect on the conversion result and the TUE has to be calculated based on the current I
the impedace of the analog source R
ANn which is the reason for an additional unadjusted error AUE of the conversion result. This AUE
can increase the specified total unadjusted error TUE (Specified value: TUE = ± 2 LSB). The
voltage U∆n is nearly independent on the voltage value of the analog source.
Note:
The overload current crosstalk effect at the analog inputs decreases the analog signal voltage
supplied by the analog signal source (the crosstalk current flows into the µC). In case of a crosstalk
current at V
in combination with R
AGND
5. Calculation Example
Assumed system values:
Result:
The negative overload current I
by an additional unadjusted error, AUE = 5.8 LSB. The TUE is in the range of –7.8LSB to 3.8LSB.
Semiconductor Group
. I
ASRC
ANn
U∆n
=
I
ANn
AUE
=
U∆n / 1 LSB
TUE
=
(± 2 LSB) - AUE
> 40 Ohm the analog signal voltage is increased.
AGND
I
= -300 µA
OV4
R
= 20 kOhm
ASRC
V
= 5 V
AREF
R
= 0.1 Ohm
AGND
I
= ovf1 * I
AN5
OV4
I
= (-4.7*E-3) * (- 300 µA)
AN5
I
= 1.41 µA
AN5
U∆5
= I
* R
AN5
ASRC
U∆5
= 1.41 µA * 20 kOhm
U∆5
= 28.2 mV
AUE
= U∆n / 1 LSB
AUE
= 28.2 mV / 4.9 mV
AUE
= 5.8 LSB
of this system example can distort the real result of AN3 and AN4
OV4
Errata Sheet, C167CR-LM, ES-DB, DB, 1.1, Mh
causes an external voltage U∆n at the analog channel
* R
ASRC
[U∆n in mV and LSB in mV]
negative overload current at P5.4
resistance of the external sensor at P5.5
1 LSB = 4.9 mV
GND shift error is neglictable
and
ANx
- 9 of 11 -
Advertisement
