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ADC10 Operation
18-6
ADC10
18.2.3 Voltage Reference Generator
The ADC10 module contains a built-in voltage reference with two selectable
voltage levels. Setting REFON = 1 enables the internal reference. When
REF2_5V = 1, the internal reference is 2.5 V. When REF2_5V = 0, the
reference is 1.5 V. The internal reference voltage may be used internally and,
when REFOUT = 0, externally on pin V
REF+
.
External references may be supplied for V
R+
and V
R−
through pins A4 and A3
respectively. When external references are used, or when V
CC
is used as the
reference, the internal reference may be turned off to save power.
External storage capacitance is not required for the ADC10 reference source
as on the ADC12.
Internal Reference Low-Power Features
The ADC10 internal reference generator is designed for low power
applications. The reference generator includes a band-gap voltage source
and a separate buffer. The current consumption of each is specified separately
in the device-specific datasheet. When REFON = 1, both are enabled and
when REFON = 0 both are disabled. The total settling time when REFON
becomes set is
30 µs.
When REFON = 1, but no conversion is active, the buffer is automatically
disabled and automatically re-enabled when needed. When the buffer is
disabled, it consumes no current. In this case, the band-gap voltage source
remains enabled.
When REFOUT = 1, the REFBURST bit controls the operation of the internal
reference buffer. When REFBURST = 0, the buffer will be on continuously,
allowing the reference voltage to be present outside the device continuously.
When REFBURST = 1, the buffer is automatically disabled when the ADC10
is not actively converting, and automatically re-enabled when needed.
The internal reference buffer also has selectable speed vs. power settings.
When the maximum conversion rate is below 50 ksps, setting ADC10SR = 1
reduces the current consumption of the buffer approximately 50%.
18.2.4 Auto Power-Down
The ADC10 is designed for low power applications. When the ADC10 is not
actively converting, the core is automatically disabled and automatically
re-enabled when needed The ADC10OSC is also automatically enabled when
needed and disabled when not needed. When the core or oscillator are
disabled, they consume no current.