User Manual

Apollo3 Blue Datasheet
DS-A3-0p9p1 Page 699 of 909 2019 Ambiq Micro, Inc.
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Figure 87. Block diagram of circuitry for Reset pin
16.3 Power-on Event
An integrated power-on detector monitors the supply voltage and keeps SYSRESETn asserted while VDD
is below the rising power-on voltage, V
POR+
(1.755 V). When VDD rises above V
POR
at initial power on,
the reset module will initialize the low power analog circuitry followed by de-assertion of SYSRESETn, and
normal operation proceeds. SYSRESETn is re-asserted as soon as VDD falls below the falling power-on
voltage, V
POR-
(1.755 V). The power-on reset signal, PORn, is not maskable.
16.4 Brown-out Events
There are multiple brownout detectors in Apollo3. An integrated brown-out detector monitors the primary
supply voltage and causes an automatic and non-configurable reset when the voltage has fallen below the
1.755 V threshold. An optional reset or interrupt can be enabled when the brown-out detector indicates the
supply voltage has fallen below the 2.1 V threshold. In addition, there are individual brownout detector
monitors integrated within the core/memory and BLE supply regulators which cause separate/maskable
reset assertions when the voltage falls below critical level for the respective voltage rails. In the event the
primary supply voltage falls below the 1.755 V threshold, or 2.1 V threshold or any of the core/memory/BLE
thresholds if enabled, the reset module will initiate a system reset, enabling the RSTn pull-down and
driving the reset pin low. A 1.755 V or 2.1 V BOD reset will be reflected by the setting of the BORSTAT bit
in the RSTGEN's STAT Register after reset.
In the event of a brownout detection, the following functionality is maintained until a power down detection
occurs.
▪ All RTC registers retain state
▪ RTC and STIMER counters continue operation from 32kHz XTAL or from LFRC (if below BODL). If clock
sources stop oscillating at very low voltage, the RTC and STIMER will continue to maintain state.
▪ Clock configuration registers retain state
Strong
Pull
Down
RSTn
RST
Button
VDD
RSTGEN
RSTn
brownout_n
RSTn Pad IO