SAFC515LN Datasheet, PDF (108/160 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C515
The external reference voltage supply need only be applied when the A/D converter is used,
otherwise the pins V_AREF and V_AGND may be left unconnected. The reference voltage supply has to
meet some requirements concerning the level of V_AGND and V_AREF and the output impedance of the
supply voltage (see also "A/D Converter Characteristics" in the data sheet).
– The voltage V_AREF must meet the following specification :
V_AREF = V_CC + 0.25 V
– The voltage V_AGND must meet a similar specification :
V_AGND = V_SS + 0.2 V
– The differential output impedance of the analog reference supply voltage should be less than
1 kW.
lf the above mentioned operating conditions are not met the accuracy of the converter may be
decreased.
Furthermore, the analog input voltage V_AINPUT must not exceed the range from (V_AGND – 0.2 V) to
(V_AREF + 0.2 V). Otherwise, a static input current might result at the corresponding analog input
which will also affect the accuracy of the other input channels.
Semiconductor Group
6-65