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Electrical Characteristics
ST10F252M
27.7.1
Conversion timing control
When a conversion is started, first the capacitances of the converter are loaded via the
respective analog input pin to the current analog input voltage. The time to load the
capacitances is referred to as sample time. Next the sampled voltage is converted to a
digital value several successive steps, which correspond to the 10-bit resolution of the ADC.
During these steps the internal capacitances are repeatedly charged and discharged via the
VAREF pin.
The current that has to be drawn from the sources for sampling and changing charges
depends on the time that each respective step takes, because the capacitors must reach
their final voltage level within the given time, at least with a certain approximation. The
maximum current, however, that a source can deliver, depends on its internal resistance.
The time that the two different actions during conversion take (sampling, and converting)
can be programmed within a certain range in the ST10F252M relative to the CPU clock. The
absolute time that is consumed by the different conversion steps therefore is independent
from the general speed of the controller. This allows adjustment of the ST10F252M A/D
converter to the system’s properties:
RSW
CC
–
600
1600
W
Port5
Port1
RAD
CC
–
1300
W
1.
VAREF can be tied to ground when A/D Converter is not in use: There is increased consumption (approximately 200A) on
main VDD due to internal analog circuitry not being completely turned off. Therefore, it is suggested to maintain the VAREF
at VDD level even when not in use, and to eventually switch off the A/D Converter circuitry setting bit ADOFF in ADCON
register.
2.
VAIN may exceed VAGND or VAREF up to the absolute maximum ratings. However, the conversion result in these cases will
be 0x000H or 0x3FFH, respectively
3.
Not 100% tested, guaranteed by design characterization
4.
During the sample time the input capacitance CAIN can be charged/discharged by the external source. The internal
resistance of the analog source must allow the capacitance to reach its final voltage level within tS. After the end of the
sample time tS, changes of the analog input voltage have no effect on the conversion result.
5.
This parameter includes the sample time tS, the time for determining the digital result and the time to load the result register
with the conversion result. Values for the conversion clock tCC depend on programming and can be taken from the next
6.
DNL, INL, OFS and TUE are tested at VAREF = 5.0V, VAGND = 0V, VDD = 5.0V. It is guaranteed by design characterization
for all other voltages within the defined voltage range.
‘LSB’ has a value of VAREF/1024.
For Port5 channels, the specified TUE (± 2LSB) is guaranteed also with an overload condition (see IOV specification)
occurring on maximum 2 not selected analog input pins of Port5 and the absolute sum of input overload currents on all
Port5 analog input pins does not exceed 10mA.
For Port1 channels, the specified TUE is guaranteed when no overload condition is applied to Port1 pins: when an overload
condition occurs on maximum 2 not selected analog input pins of Port1 and the input positive overload current on all analog
input pins does not exceed 10mA (either dynamic or static injection), the specified TUE is degraded (± 7LSB). To obtain the
same accuracy, the negative injection current on Port1 pins must not exceed -1mA in case of both dynamic and static
injection.
7.
The coupling factor is measured on a channel while an overload condition occurs on the adjacent not selected channels
with the overload current within the different specified ranges (for both positive and negative injection current).
8.
Table 148.
A/D converter characteristics (continued)
Parameter
Symbol
Limit values
Unit
Test condition
Min
Max