AN3433 datasheet(16/34 Pages) STMICROELECTRONICS

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Power consumption considerations

AN3433

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Doc ID 019046 Rev 2

Power consumption considerations

This chapter describes the advantages and benefits for using the various Idle command

parameters to select the best wakeup configuration for your device to ensure optimal power

consumption for your application.

The previous chapter describes how to use the Idle command to set the device from Ready

to one of the three WFE modes (Hibernate, Sleep, and Tag Detector). The following sections

describe the various wakeup processes for the selected WFE mode.

3.1

Transition from Ready to Hibernate state

Hibernate state consumes the least amount of power of all the possible device states.

Only an Idle command can set the device from Ready state to Hibernate state. After

receiving the Hibernate command via the SPI bus, the device (Figure 2) stops the oscillator

and analog resources and the device enters Hibernate state.

A basic Idle command to set the device from Ready state to Hibernate state is:

>>> 0x07 0E 08 04 00 04 00 18 00 00 00 00 00 00 00 00

In Hibernate state, the device minimizes its power consumption by disabling most of its

resources before stopping the external oscillator. In this state, power consumption will

decrease from approximately 2.5 mA to less than 2 µA.

The only way the device can wakeup from Hibernate state is by an external event (pin

IRQ_IN goes low).

The device will only send its response after having returned to Ready state after an external

event is detected.

When the device wakes up from Hibernate state (Figure 3), it restarts the external oscillator

and all other resources, including the selected communication interface, before returning to

Ready state and waiting for a new command.

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