AN3433 datasheet(12/34 Pages) STMICROELECTRONICS

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Management of CR95HF or STRFNFCA activity

AN3433

12/34

Doc ID 019046 Rev 2

2.6

Using various techniques to return to Ready state

The Idle command and reply set offers several benefits to users by enabling various

methods to return the CR95HF or STRFNFCA to Ready state. Some methods are nearly

automatic, such as waiting for a timer overflow or a tag detection, but others consume more

power compared to the ones requesting a host action. A description of each method follows

below.

2.6.1

Default setting: from POR to Ready state

After power-on, the CR95HF or STRFNFCA enters Power-up state.

To wake up the device and set it to Ready state, the user must send a low pulse on the

IRQ_IN pin. The device then automatically selects the external interface (SPI or UART) and

enters Ready state and is able to accept commands after a delay of approximately 3 ms.

2.6.2

From Ready state to Hibernate state and back to Ready state

In Hibernate state, most resources are switched off to achieve an ultra-low power

consumption.

The only way the CR95HF or STRFNFCA can wake up from Hibernate state is by an

external event (low pulse on pin IRQ_IN).

A basic Idle command is:

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

Note:

The Wakeup flag value is NOT significant when returning to Ready state from Hibernate

state or after a POR.

2.6.3

From Ready state to Sleep state and back to Ready state

Wake up by external event (low pulse on IRQ_IN or SPI_SS pin)

In Sleep or Power-up states, operating resources are limited in function of the selected

wakeup source to achieve a moderate power consumption level.

An Idle command example when wakeup source is pin IRQ_IN:

>>>0x07 0E 08 01 00 38 00 18 00 00 60 00 00 00 00 00

A similar command can be implemented using pin SPI_SS as a wakeup source:

>>>0x07 0E 10 01 00 38 00 18 00 00 60 00 00 00 00 00

Wakeup by Timeout

The LFO is required to use the timer. However, this increases the typical power consumption

by 80 µA. Several parameters can be modified to reduce power consumption as much as

possible.

The Duration before Timeout is defined by parameters WU period and MaxSleep,

respectively 0x60 and 0x08 in the following example.

Duration before Timeout = 256 * tL * (WU period + 2) * (MaxSleep + 1)

Note:

Note that: 0x00 < MaxSleep < 0x1F.

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