Rev. 1.10
106
November 26, 2019
Rev. 1.10
107
November 26, 2019
HT68FB240
USB Low Speed Flash MCU
LVD Operation
The Low Voltage Detector function operates by comparing the power supply voltage, V
DD
, with a
pre-specified voltage level stored in the LVDC register. This has a range of between 2.0V and 4.0V.
When the power supply voltage, V
DD
, falls below this pre-determined value, the LVDO bit will be
set high indicating a low power supply voltage condition. The Low Voltage Detector function is
supplied by a reference voltage which will be automatically enabled. When the device is powered
down the low voltage detector will remain active if the LVDEN bit is high. After enabling the Low
Voltage Detector, a time delay t
LVDS
should be allowed for the circuitry to stabilise before reading the
LVDO bit. Note also that as the V
DD
voltage may rise and fall rather slowly, at the voltage nears that
of V
LVD
, there may be multiple bit LVDO transitions.
LVD Operation
The Low Voltage Detector also has its own interrupt which is contained within one of the Multi-
function interrupts, providing an alternative means of low voltage detection, in addition to polling
the LVDO bit. The interrupt will only be generated after a delay of t
LVD
after the LVDO bit has been
set high by a low voltage condition. When the device is powered down the Low Voltage Detector
will remain active if the LVDEN bit is high. In this case, the LVF interrupt request flag will be set,
causing an interrupt to be generated if V
DD
falls below the preset LVD voltage. This will cause the
device to wake-up from the SLEEP or IDLE Mode, however if the Low Voltage Detector wake up
function is not required then the LVF flag should be first set high before the device enters the SLEEP
or IDLE Mode.
When LVD function is enabled, it is recommenced to clear LVD flag first, and then enables interrupt
function to avoid mistake action.