ST25R3916 datasheet(17/157 Pages) STMICROELECTRONICS

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DS12484 Rev 4

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ST25R3916/7

Description

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reference value by more than a register defined threshold then an interrupt is sent to the

external controller.

2.2.7

External field detector

This is a low power block used in the active or passive target mode to detect the presence of

an external RF field. It supports two different external field detection thresholds, namely

Peer detection and Collision avoidance threshold.

The Peer detection threshold is used in the active and passive peer to peer modes to detect

when the peer device turns on its RF field.

The Collision avoidance threshold is used to detect the presence of an external RF field

during the RF collision avoidance procedure.

2.2.8

Quartz crystal oscillator

The quartz crystal oscillator operates with 27.12 MHz crystals. At start-up the

transconductance of the oscillator is increased to achieve a fast start-up. Since the start-up

time varies with crystal type, temperature and other parameters, the oscillator amplitude is

observed and an interrupt is generated when stable oscillator operation is reached.

The oscillator block also provides a clock signal to the external microcontroller (MCU_CLK),

according to the settings in the IO configuration register 1.

2.2.9

Power supply regulators

The integrated power supply regulators ensures a high power supply rejection ratio (PSRR)

for the complete system.

Three voltage regulators, one for the analog block, one for the digital block, and one for the

RF output drivers, are available to decouple noise sources from the ST25R3916/7. A fourth

voltage regulator generates the reference voltage for the analog receivers (AGDC, analog

ground).

The RF output driver voltage regulator can be configured automatically by the ST25R3916/7

based on the systems power supply stability and RF output power (see Section 4.4.10:

Adjust regulators for more details).

2.2.10

POR and bias

This block provides bias currents and reference voltages to all other blocks. It also

incorporates a Power on Reset (POR) circuit that provides a reset at power-up and at low

supply levels.

2.2.11

RC oscillator and Wake-up timer

The ST25R3916/7 include several possibilities for low power detection of a card presence

(capacitive sensor, phase measurement, amplitude measurement). The RC oscillator and

the register configurable Wake-up timer are used to periodically trigger the card presence

detection in the low power card detection modes.

Note:

Using hardware based wake-up in combination with the automatic antenna tuning feature is

not recommended. Contact your nearest ST office for further support.

ST25R3916 Datasheet(PDF) 17 Page - STMicroelectronics

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