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ST6215C/ST6225C
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5.2 LOW VOLTAGE DETECTOR (LVD)
The on-chip Low Voltage Detector is enabled by
setting a bit in the option bytes (refer to the Option
Bytes section of this document).
The LVD allows the device to be used without any
external RESET circuitry. In this case, the RESET
pin should be left unconnected.
If the LVD is not used, an external circuit is manda-
tory to ensure correct Power On Reset operation,
see figure in the Reset section. For more details,
please refer to the application note AN669.
The LVD generates a static Reset when the supply
voltage is below a reference value. This means
that it secures the power-up as well as the power-
down keeping the ST6 in reset.
The V
IT- reference value for a voltage drop is lower
than the VIT+ reference value for power-on in order
to avoid a parasitic reset when the MCU starts run-
ning and sinks current on the supply (hysteresis).
The LVD Reset circuitry generates a reset when
VDD is below:
– V
IT+ when V
DD is rising
– V
IT- when V
DD is falling
If the LVD is enabled, the MCU can be in only one
of two states:
– Over the input threshold voltage, it is running un-
der full software control
– Below the input threshold voltage, it is in static
safe reset
In these conditions, secure operation is guaran-
teed without the need for external reset hardware.
During a Low Voltage Detector Reset, the RESET
pin is held low, thus permitting the MCU to reset
other devices.
Figure 12. Low Voltage Detector Reset
VDD
VIT+
RESET
VIT-
Vhyst
1