Rev. 1.40
86
March 29, 2019
Rev. 1.40
87
March 29, 2019
HT45F23A/HT45F24A
TinyPower
TM
Flash MCU with OPA & Comparators
HT45F23A/HT45F24A
TinyPower
TM
Flash MCU with OPA & Comparators
A/D Conversion Timing
Programming Considerations
During microcontroller operations where the A/D converter is not being used, the A/D internal
circuitry can be switched off to reduce power consumption, by setting bit ADONB high in the ACSR
register. When this happens, the internal A/D converter 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 Transfer Function
As the devices contain a 12-bit A/D converter respectively, its full-scale converted digitised value is
equal to FFFH. Since the full-scale analog input value is equal to the V
DD
or V
REF
voltage, this gives
a single bit analog input value of V
DD
or V
REF
divided by 4096.
1 LSB= (V
DD
or V
REF
)
÷ 4096
The A/D Converter input voltage value can be calculated using the following equation:
A/D input voltage = A/D output digital value × (V
DD
or 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
DD
or V
REF
level.