Datasheet

DS9178 Rev 4 15/96
STM8L051F3 Functional overview
41
3.3 Reset and supply management
The power supplies requirements must be defined in order to have a correct microcontroller
operation. The reset and supply management controls the microcontroller operation under
defined conditions.
3.3.1 Power supply scheme
The device requires a 1.8 V to 3.6 V operating supply voltage (V
DD
). The external power
supply pins must be connected as follows:
• V
SS1
; V
DD1
= 1.8 to 3.6 V: external power supply for I/Os and for the internal regulator.
Provided externally through V
DD1
pins, the corresponding ground pin is V
SS1
.
• V
SSA
; V
DDA
= 1.8 to 3.6 V: external power supplies for analog peripherals. V
DDA
and
V
SSA
must be connected to V
DD1
and V
SS1
, respectively.
• V
SS2
; V
DD2
= 1.8 to 3.6 V: external power supplies for I/Os. V
DD2
and V
SS2
must be
connected to V
DD1
and V
SS1
, respectively.
• V
REF+
, V
REF-
(for ADC1): external reference voltage for ADC1. Must be
providedexternally through V
REF+
and V
REF-
pin.
3.3.2 Power supply supervisor
The device has an integrated ZEROPOWER power-on reset (POR)/power-down reset
(PDR), coupled with a brownout reset (BOR) circuitry. When the microcontroller operates
between 1.8 and 3.6
V, BOR is always active and ensures proper operation starting from
1.8
V. After the 1.8 V BOR threshold is reached, the option byte loading process starts,
either to confirm or modify default thresholds, or to disable BOR permanently.
Five BOR thresholds are available through option bytes, starting from 1.8 V to 3 V. To
reduce the power consumption in Halt mode, it is possible to automatically switch off the
internal reference voltage (and consequently the BOR) in Halt mode. The device remains in
reset state when V
DD
is below a specified threshold, V
POR/PDR
or V
BOR
, without the need for
any external reset circuit.
The device features an embedded programmable voltage detector (PVD) that monitors the
V
DD
/V
DDA
power supply and compares it to the V
PVD
threshold. This PVD offers 7 different
levels between 1.85
V and 3.05 V, chosen by software, with a step around 200 mV. An
interrupt can be generated when V
DD
/V
DDA
drops below the V
PVD
threshold and/or when
V
DD
/V
DDA
is higher than the V
PVD
threshold. The interrupt service routine can then generate
a warning message and/or put the MCU into a safe state. The PVD is enabled by software.
3.3.3 Voltage regulator
STM8L051F3 as all the low density value line STM8L05xxx embeds an internal voltage
regulator for generating the 1.8 V power supply for the core and peripherals.
This regulator has two different modes:
• Main voltage regulator mode (MVR) for Run, Wait for interrupt (WFI) and Wait for event
(WFE) modes.
• Low-power voltage regulator mode (LPVR) for Halt, Active-halt, Low-power run and
Low-power wait modes.
When entering Halt or Active-halt modes, the system automatically switches from the MVR
to the LPVR in order to reduce current consumption.
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