EM78P5840N/41N/42N
8-Bit Microcontrollers
10.2 10-Bit ADC Characteristics
The EM78P5840N/41N/42N has a built-in 10-bit resolution, multichannel ADC function.
In an ideal situation, if ADC’s reference voltage is 5V, the ADC’s LSB is 5V/1024.
However, due to some physical or circuit characteristics, the convertion result may be
adversely affected. An example is shown in the next figure. The offset voltage reduces
the AD’s converter range. If the AD’s input voltage is less than VOFL, the ADC will
output a “0.” On the other hand, if the input voltage is larger than (VDD-VOFH), the
ADC will output 1023. That is , the AD converter range will be replaced by
(VDD-VOFH+LSB-VOFL+LSB).
If VRB = VOFL – LSB and
VRT = VDD-VOFH+LSB, then LSB is:
LSB = (VRT – VRB) / 1024
LSB = (VDD – (VOFH+VOFL) ) / 1022
NOTE
During actual operation, carefully observe the resulting effect of the AD offset voltage.
When the converter range is VRT ~ VRB, the AD converter’s result will be more
precised.
10-bit ADC
VDD
VRT
VOFH
Min. input for ADC output = 1023
(For 10-bit ADC, internally it takes this range to
average 1024 steps)
Min. input for ADC output = 1
VOFL
VRB
0V
Figure 9-3 Relationhip between ADC and Offset Voltage
52 •
Product Specification (V1.0) 04.25.2006
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
