RFM24W Datasheet, PDF (17/34 Pages) List of Unclassifed Manufacturers – ISM Transceiver module

RFM24W
3.3.1. SHUTDOWN State
The SHUTDOWN state is the lowest current consumption state of the device with nominally less than 20 nA of
current consumption. The shutdown state may be entered by driving the SDN pin (Pin 1) high. The SDN pin should
be held low in all states except the SHUTDOWN state. In the SHUTDOWN state, the contents of the registers are
lost and there is no SPI access. When coming out of the SHUTDOWN state a power on reset (POR) will be
initiated along with the internal calibrations.
3.3.2. IDLE States
There are five different modes in the IDLE state which may be commanded. All modes have a tradeoff between
current consumption and response time to TX/RX mode. This tradeoff is shown in Table 9. After the POR event,
SWRESET, or exiting from the SHUTDOWN state the chip will default to the IDLE-READY mode.
3.3.3. STANDBY Mode
STANDBY mode has the lowest current consumption of the five IDLE states. In this state the register values are
maintained with all other blocks disabled. The SPI is accessible during this mode but an SPI event will enable an
internal boot oscillator and automatically move the part to SPI ACTIVE mode. After an SPI event the host will need
to re-command the device back to STANDBY mode through the “Change State” API command to achieve the
100 nA current consumption. If an interrupt has occurred (i.e., the nIRQ pin = 0) the interrupt registers must be
read to achieve the minimum current consumption of this mode.
3.3.4. SLEEP Mode
In SLEEP mode the Wake-Up-Timer and a 32 kHz clock source are enabled. The source of the 32 kHz clock can
either be an internal 32 kHz RC oscillator which is periodically calibrated or a 32 kHz oscillator using an external
XTAL.The SPI is accessible during this mode but an SPI event will enable an internal boot oscillator and
automatically move the part to SPI ACTIVE mode. After an SPI event the host will need to re-command the device
back to SLEEP. If an interrupt has occurred (i.e., the nIRQ pin = 0) the interrupt registers must be read to achieve
the minimum current consumption of this mode.
3.3.5. SPI ACTIVE Mode
In SPI ACTIVE mode the SPI and a boot up oscillator are enabled. After SPI transactions during either STANDBY
or SLEEP mode the device will not automatically return to these modes. A “Change State” API command will be
required to return to either the STANDBY or SLEEP modes.
3.3.6. READY Mode
READY Mode is designed to give a fast transition time to TX or RX state with reasonable current consumption. In
this mode the Crystal oscillator remains enabled reducing the time required to switch to TX or RX mode by
eliminating the crystal start-up time.
3.3.7. TX State
The TX state may be entered from any of the IDLE modes by using the “Start TX” or “Change State” API command.
A built-in sequencer takes care of all the actions required to transition between states from enabling the crystal
oscillator to ramping up the PA. The following sequence of events will occur automatically when going from
STANDBY mode to TX mode.
1. Enable the digital LDO and the analog LDOs.
2. Start up crystal oscillator and wait until ready (controlled by an internal timer).
3. Enable PLL.
4. Calibrate VCO/PLL.
5. Wait until PLL settles to required transmit frequency (controlled by an internal timer).
6. Activate power amplifier and wait until power ramping is completed (controlled by an internal timer).
7. Transmit packet.
Steps in this sequence may be eliminated depending on which IDLE mode the chip is configured to prior to
commanding to TX. By default, the VCO and PLL are calibrated every time the PLL is enabled. When the “Start
TX” API command is utilized the next state may be defined to ensure optimal timing and turnaround.
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