ST72104G, ST72215G, ST72216G, ST72254G
7.1 LOW VOLTAGE DETECTOR (LVD)
To allow the integration of power management
features in the application, the Low Voltage Detec-
tor function (LVD) generates a static reset when
In these conditions, secure operation is always en-
sured for the application without the need for ex-
ternal reset hardware.
the V
supply voltage is below a V reference
DD
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During a Low Voltage Detector Reset, the RESET
pin is held low, thus permitting the MCU to reset
other devices.
value. This means that it secures the power-up as
well as the power-down keeping the ST7 in reset.
The V reference value for a voltage drop is lower
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Notes:
than the V reference value for power-on in order
1. The LVD allows the device to be used without
any external RESET circuitry.
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to avoid a parasitic reset when the MCU starts run-
ning and sinks current on the supply (hysteresis).
2. Three different reference levels are selectable
through the option byte according to the applica-
tion requirement.
The LVD Reset circuitry generates a reset when
V
is below:
DD
LVD application note
– V when V is rising
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DD
– V when V is falling
The LVD function is illustrated in the Figure 9.
Application software can detect a reset caused by
the LVD by reading the LVDRF bit in the CRSR
register.
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DD
Provided the minimum V value (guaranteed for
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This bit is set by hardware when a LVD reset is
generated and cleared by software (writing zero).
the oscillator frequency) is above V , the MCU
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can only be in two modes:
– under full software control
– in static safe reset
Figure 9. Low Voltage Detector vs Reset
V
DD
V
hyst
V
V
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RESET
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