AS8221
Data Sheet - Detailed Description
8.5 Undervoltage Events
The device monitors the following three voltage supplies:
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VBAT: Battery supply voltage
VIO: Supply voltage for I/O digital level adaptation
VCC: Supply voltage (+5V)
8.5.1 Undervoltage/Voltage Recovery VBAT
If VBAT voltage falls below VBATTHL for a time longer than tUV_DETECT then the undervoltage VBAT flag is set and it is reset if VBAT exceeds the
voltage threshold VBATTHH for a time longer than tUV_REC or in case a wake-up event has been detected. The flag can be set or reset in all the
modes.
8.5.2 Undervoltage/Voltage Recovery VIO
If VIO voltage falls below VIOTHL for a time longer than tUV_DETECT then the undervoltage VIO flag is set and it is reset if VIO exceeds the voltage
threshold VIOTHH for a time longer than tUV_REC or in case a wake-up event has been detected. The flag can be set or reset in all the operation
modes. The flag is automatically reset at POWER-OFF.
8.5.3 Undervoltage/Voltage Recovery VCC
If VCC voltage falls below VCCTHL for a time longer than tUV_DETECT then the undervoltage VCC flag is set and it is reset if VCC exceeds the
voltage threshold VCCTHH for a time longer than tUV_REC or in case a wake-up event has been detected. The flag can be set or reset in all
operation modes. The flag is automatically reset at POWER-OFF.
8.6 Power On/Off Events
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Starting from POWER-OFF mode a power on event occurs in case VBAT undervoltage flag is reset.
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Starting from every operation mode a POWER-OFF event occurs in case VBAT and VCC undervoltage flags are set.
8.7 Wake-Up Events
A wake-up event can be detected only in low-power modes. The wake-up flag is set if the remote or local wake flag is set. The wake-up flag is
reset if both the remote and local wake-up flags are reset. The remote wake-up flag is set if a remote wake-up event occurs. The local wake-up
flag is set if a local wake-up event occurs. The remote and local wake-up flags are reset entering a low-power mode from a non-low-power mode,
entering NORMAL mode, whenever an undervoltage event occurs and at POWER-OFF.
8.7.1 Remote Wake-Up Event
A remote wake-up event, only possible in low-power mode, consists in the reception of at least two consecutive wake-up symbols via the bus
within tBWU_Detect. The wake-up symbol is defined as Data0 longer than tBWU_D0 followed by idle or Data1 longer than tBWU_Idle as in Figure 7
unless an undervoltage or wake-up event is present.
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