HT68F03 datasheet(122/139 Pages) HOLTEK

122 / 139 page

HT66F03/HT66F04/HT68F03/HT68F04

Rev. 1.00

122

April 16, 2010

LVD Operation

The Low Voltage Detector function operates by compar-

ing the power supply voltage, VDD, with a pre-specified

voltage level stored in the LVDC register. This has a

range of between 2.0V and 4.4V. When the power sup-

ply voltage, VDD, falls below this pre-determined value,

the LVDO bit will be set high indicating a low power sup-

ply voltage condition. The Low Voltage Detector func-

tion 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 De-

tector, a time delay tLVDS should be allowed for the cir-

cuitry to stabilise before reading the LVDO bit. Note also

that as the VDD voltage may rise and fall rather slowly, at

the voltage nears that of VLVD, there may be multiple bit

LVDO transitions.

The Low Voltage Detector also has its own interrupt

which is contained within one of the Multi-function inter-

rupts, providing an alternative means of low voltage de-

tection, in addition to polling the LVDO bit. The interrupt

will only be generated after a delay of tLVD 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 in-

terrupt to be generated if VDD 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 De-

tector wake up function is not required then the LVF flag

should be first set high before the device enters the

SLEEP or IDLE Mode.

V D D

V L V D

L V D E N

L V D O

t L V D S

LVD Operation

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