SI4464 datasheet(21/56 Pages) SILABS

21 / 56 page

Si4464/63/61/60

Rev 1.2

3.3.2. Shutdown State

The shutdown state is the lowest current consumption state of the device with nominally less than 30 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. After the POR the POWER_UP command is required to initialize the radio. The SDN pin

needs to be held high for at least 10us before driving low again so that internal capacitors can discharge. Not

holding the SDN high for this period of time may cause the POR to be missed and the device to boot up incorrectly.

If POR timing and voltage requirements cannot be met, it is highly recommended that SDN be controlled using the

host processor rather than tying it to GND on the board.

3.3.3. Standby State

Standby state has the lowest current consumption with the exception of shutdown but has much faster response

time to RX or TX mode. In most cases standby should be used as the low power state. In this state the register

values are maintained with all other blocks disabled. The SPI is accessible during this mode but any SPI event,

including FIFO R/W, will enable an internal boot oscillator and automatically move the part to SPI active state. After

an SPI event the host will need to re-command the device back to standby through the “Change State” API

command to achieve the 50 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 State

Sleep state is the same as standby state but 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 State

In SPI active state the SPI and a boot up oscillator are enabled. After SPI transactions during either standby or

sleep the device will not automatically return to these states. A “Change State” API command will be required to

return to either the standby or sleep modes.

3.3.6. Ready State

Ready state 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 state with the “Start TX” or “Change State” API commands. 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 to TX state.

1. Enable internal LDOs.

2. Start up crystal oscillator and wait until ready (controlled by an internal timer).

Table 10. POR Timing

Variable

Description

Min

Typ

Max

Units

tPORH

High time for VDD to fully settle POR circuit

tPORL

Low time for VDD to enable POR

VRRH

Voltage for successful POR

90%*Vdd

VRRL

Starting Voltage for successful POR

0150

tSR

Slew rate of VDD for successful POR

1ms

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