Rev. 1.00
126
September 11, 2018
Rev. 1.00
127
September 11, 2018
HT45F4050
A/D NFC Flash MCU
HT45F4050
A/D NFC Flash MCU
Programming Considerations
During microcontroller operations where the A/D converter is not being used, the A/D conversion
internal circuitry can be switched off to reduce power consumption, by clearing the ADCEN bit
in the SADC0 register. When this happens, the internal A/D conversion circuits will not consume
power irrespective of what analog voltage is applied to their input lines. If the A/D converter input
lines are used as normal I/Os, then care must be taken as if the input voltage is not at a valid logic
level, then this may lead to some increase in power consumption.
A/D Conversion Function
As the device contains a 12-bit A/D converter, its full-scale converted digitised value is equal to
FFFH. Since the full-scale analog input value is equal to the actual A/D converter reference voltage,
V
REF
, this gives a single bit analog input value of
V
REF
divided by 4096.
1 LSB=V
REF
÷ 4096
The A/D Converter input voltage value can be calculated using the following equation:
A/D converter input voltage=A/D converter output digital value ×
V
REF
÷ 4096
The diagram shows the ideal transfer function between the analog input value and the digitised
output value for the A/D converter. Except for the digitised zero value, the subsequent digitised
values will change at a point 0.5 LSB below where they would change without the offset, and the
last full scale digitised value will change at a point 1.5 LSB below the V
REF
level.
Note that here the
V
REF
voltage is the actual A/D converter reference voltage determined by the SAVRS field.
Note that here the
V
REF
voltage is the actual A/D converter reference voltage determined by the
SAVRS bit field.
FFFH
FFEH
FFDH
03H
02H
01H
0
1
2
3
4093 4094 4095 4096
V
REF
4096
Analog Input Voltage
A/D Conversion
Result
1.5 LSB
0.5 LSB
Ideal A/D Conversion Function