AN3433 datasheet(10/34 Pages) STMICROELECTRONICS

10 / 34 page

Management of CR95HF or STRFNFCA activity

AN3433

10/34

Doc ID 019046 Rev 2

2.4

Using LFO frequency setting to reduce power consumption

In WFE mode, the high frequency oscillator (HFO) is stopped and most processes being

executed are clocked by the low frequency oscillator (LFO). To minimize CR95HF or

STRFNFCA power consumption in WFE mode, the slower the LFO frequency, the lower the

power consumption.

Example 1: Setting a lower LFO frequency

The following equation defines a basic timing reference:

tREF = 256*tL ms (where tL = 1/fLFO)

tREF = 8 ms (when bits [7:6] are set to ‘00’, or 32 kHz)

tREF = 64 ms (when bits [7:6] are set to ‘11’, or 4 kHz)

Leave Control

These two bytes (LeaveCtrlL and LeaveCtrlH) define the resources when

returning to Ready state.

0x1800: Hibernate

0x1800: Sleep

0x1800: Tag Detector Calibration

0x1800: Tag detection

WU Period

This byte is the coefficient used to adjust the time allowed between two tag

detections. Also used to specify the duration before timeout. (Typical value:

0x20)

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

Osc Start

This byte defines the delay for HFO stabilization. (Recommended value:

0x60)

Defines the Wait time for HFO to stabilize: <OscStart> * tL

DAC Start

This byte defines the delay for DAC stabilization. (Recommended value:

0x60)

Defines the Wait time for DAC to stabilize: <DacStart> * tL

DAC Data

These two bytes (DacDataL and DacDataH) define the lower and higher

comparator values, respectively. These values are determined by a

calibration process.

When using the device demoboard, these values should be set to

approximately

0x64 and 0x74, respectively.

Swing Count

This byte defines the number of HF swings allowed during Tag Detection.

(Recommended value:

0x3F)

Max Sleep

This byte defines the maximum number of tag detection trials or the

coefficient to adjust the maximum inactivity duration before timeout.

MaxSleep must be: 0x00 < MaxSleep < 0x1F

This value must be set to

0x01 during the Tag Detection Calibration

process.

Also used to specify duration before timeout.

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

(Typical value: 0x28)

Table 6.

Summary of parameters (continued)

Parameter

Description

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