LR1121
User Manual Rev 1.1
UM.LR1121.W.APP Mar 2023
17 of 130
Semtech
Proprietary & Confidential
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2.1.5 Sleep
Sleep mode configures the LR1121 into a low power consumption mode between radio operations, while retaining the
configuration register values and storing the firmware data in RAM. The BUSY signal is set to 1 with a pull-up and all MISO
SPI signals are high-Z when the LR1121 is in sleep mode. In sleep mode, all DIOs are in Hi-Z mode.
An optional 32kHz source can run either on the internal RC oscillator, or on the internal 32.768kHz oscillator driving an
external crystal. The 32.768kHz crystal oscillator allows a faster transition to standby mode, at the expense of higher power
consumption. In both cases, the RTC uses the 32kHz clock source to allow an automatic wake-up from Sleep mode.
2.1.5.1 SetSleep
SetSleep(...) puts the device in Powerdown or Sleep mode, and configures the timeout for automatic wake-up.
• SleepConfig defines in which sleep mode the device is put, and if it wakes up after a given time on the RTC event:
Retention (bit 0) defines if the device configuration and firmware data are retained:
1: 8kB of memory used for device state and firmware data retention
0: No data retention (Power Down mode)
Wakeup (bit 1) determines if the device wakes up after a given time on the RTC event:
1: Automatic wake-up enabled. Device automatically goes in Standby mode with RC oscillator, at end of
SleepTime timer. Configure the 32kHz clock source using command ConfigLfClock (...) for modem
applications.
0: Automatic wake-up disabled
Other bits are RFU and should be set to 0
• SleepTime: sleep time in number of 32.768kHz clock cycles, prior to automatic wake-up. Therefore, the sleep time can
vary from 0ms to 36.4 hours in steps of 30.52us
The device exits this mode upon the falling edge on the NSS signal even when automatic wakeup is enabled. Exiting this
mode, the device performs a firmware restart. When the BUSY signal is set to low, it indicates that the startup phase has
been performed successfully, and that the device is ready to accept a command.
The following table summarizes the sleep modes according to Retention and Wakeup bits configuration, with their current
consumption (RC /XTAL) and Standby transitions times (indicative values, for comparison only).
Table 2-6: SetSleep Command
Byte 0 1 2 3 4 5 6
Data from Host 0x01 0x1B SleepConfig SleepTime(31:24) SleepTime(23:16) SleepTime(15:8) SleepTime(7:0)
Data to Host Stat1 Stat2 IrqStatus (31:24) IrqStatus (23:16) IrqStatus (15:8) IrqStatus (7:0) 0x00
Table 2-7: SleepConfig Parameter
SleepConfig bit bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
Definition RFU RFU RFU RFU RFU RFU Wakeup Retention
Table 2-8: Sleep Mode Summary
Retention Wakeup Datasheet Indicative Consumption (uA) Indicative Transition to Stby (ms)
0 0 Powerdown IDDPDN 30
0 1 Sleep IDDSL1 / IDDSL2 30
1 0 RFU - -
1 1 Sleep w/ 8 kB retention IDDSL3A / IDDSL4A <1
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