HT45F3420 Datasheet, PDF (91/141 Pages) Holtek Semiconductor Inc – Personal Care Flash MCU

HT45F3420/HT45F3430
Personal Care Flash MCU
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 clearing the ENADC bit in the
SADC0 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 Conversion Transfer Function
As the devices contain 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 reference voltage, VREF, which can be
VDD, VREF pin voltage or VR, this gives a single bit analog input value of reference voltage value
divided by 4096.
1 LSB= VREF/ 4096
The A/D Converter input voltage value can be calculated using the following equation:
A/D input voltage=A/D output digital value × (VREF/ 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 VREF level.
FFFH
FFEH
FFD H
A /D C o n v e r s io n
R e s u lt
03H
02H
01H
0 .5 L S B
1 .5 L S B
0
1
2
3
4093 4094 4095 4096
A n a lo g In p u t V o lta g e
Ideal A/D Transfer Function
(
V REF
4096
)
Rev. 1.31
91
April 11, 2017