ST25R NFC Reader IC Guide

ST25R NFC Reader IC Guide: STMicroelectronics

STMicroelectronics' ST25R series are high-performance NFC readerNFC readerActive device generating RF field to initiate communication with tagsView full → ICs targeting industrial, medical, and multi-protocol applications. Unlike NXP's PN532/PN7150 which target consumer NFC, the ST25R chips excel at extended read rangeread rangeMaximum communication distance between reader and tagView full →, multi-protocol support (HF RFID + NFC), and precise RF control.

ST25R Family Overview

IC	Target Market	Key Differentiator
ST25R3911B	Industrial RFID / NFC	Multi-protocol, external PA support
ST25R3916	Industrial NFC (current flagship)	WLC TX, NFC-V enhanced, Active Load ModulationLoad ModulationPassive tagPassive tagBatteryless tag powered by reader's electromagnetic fieldView full → response technique varying load impedanceView full →
ST25R3916B	ST25R3916 successor	Improved EMVCo compliance, 2023
ST25R100	Automotive	AEC-Q100 Grade 2, extended temp
ST25RU3993	UHF RFID (860–960 MHz)	Not NFC — different product family

This guide focuses on the ST25R3916 as the current recommended part.

ST25R3916 Specifications

Parameter	Value
Supply voltage	3.0–4.5 V (typ 3.3 V)
Interface	SPI (up to 10 MHz) + interrupt
operating-frequency	13.56 MHz
Output power	Up to +23 dBm (with external PA)
Protocols	ISO 14443ISO 14443Standard for contactless smart cards at 13.56 MHz (Types A and B)View full → A/B, iso-15693, ISO 18000-3M3, NFC-A/B/F/V, FeliCa
Card emulation	Passive A/B/F, Active Load Modulation
Read range	Up to 12 cm (large antenna + external PA)
WLC TX	1 W wireless charging transmit
Package	VFQFPN32, 5×5 mm

Why Choose ST25R Over PN532?

Criterion	ST25R3916	PN532
Read range	Up to 12 cm (with PA)	~5 cm
Multi-protocol	ISO 14443 A/B + ISO 15693ISO 15693Standard for vicinity-range smart cards, 1+ meter read rangeView full → + FeliCa	ISO 14443 + FeliCa + ISO 15693
RF output power	Adjustable up to +23 dBm	Fixed ~20 dBm
Active Load Modulation	Yes (NFC ForumNFC ForumIndustry body developing NFC standards, specifications, and certifications since 2004View full → compliant)	No
EMVCo certification	ST sells certified modules	Requires custom cert
SDK quality	ST25R SDK (C, MISRA-compliant)	Community libraries
Cost (bare IC)	~$3–8	~$2–5

The ST25R shines in applications requiring longer range on iso-15693 tags (up to 1 m with amplified antenna), robust EMVCo compliance for payment, or precise control over RF field parameters.

SPI Interface and Register Map

The ST25R3916 uses a 5 MHz SPI interface with a register map organised into:

Address Range	Block	Purpose
0x00–0x3F	Main registers	Mode, TX/RX config, interrupt mask
0x40–0x5F	Test registers	Factory use only
0x60–0x7F	FIFO direct access	512-byte Tx/Rx FIFO

Key registers for initial configuration: - 0x00 (Operation Control): Enable receiver, transmitter, oscillator - 0x01 (Mode Definition): Select NFC-A, NFC-B, NFC-V, or NFC-F - 0x04 (Bit Rate Definition): Set 106/212/424/848 kbps - 0x28 (Tx Driver): Set antenna driver strength

ST25R SDK Integration

ST provides the RFAL (RF Abstraction Layer) library — a MISRA-C compliant, hardware-abstracted NFC stack:

#include "rfal_platform.h"
#include "rfal_nfc.h"

rfalNfcDiscoverParam discParam = {
    .devLimit      = 1,
    .techs2Find    = RFAL_NFC_POLL_TECH_A | RFAL_NFC_POLL_TECH_B
                   | RFAL_NFC_POLL_TECH_V,
    .totalDuration = 1000,  // ms
};

ReturnCode err = rfalNfcDiscover(&discParam);
rfalNfcWorker();  // Call repeatedly in main loop

rfalNfcDevice *nfcDevice;
if (rfalNfcIsDevActivated(rfalNfcGetState())) {
    rfalNfcGetActiveDevice(&nfcDevice);
    // Read NDEF...
}

RFAL is available on GitHub (ST-Hotspot/STSW-ST25R-RFAL) and is the officially supported path for new designs.

Antenna Design Considerations

The ST25R3916's output impedance is approximately 4 Ω differential. A matching network is required between the IC output and the antenna coil. ST provides RFAL-compatible antenna designantenna designEngineering NFC antennaNFC antennaCoil antenna creating electromagnetic field for NFC communicationView full → geometry for performance requirementsView full → tools and reference designs in application note AN4974.

For a 5×5 cm PCB antenna targeting ISO 14443A: - Coil: 3–5 turns, 1 mm track width, 0.5 mm spacing - Resonant capacitor: parallel capacitor to tune to 13.56 MHz - Matching network: series L + shunt C to transform antenna impedance to IC output impedance

See NFC Antenna Matching Guide for the full matching network derivation.

ST25R Discovery Loop (Multi-Protocol Polling)

The RFAL discovery loop automatically cycles through all enabled technologies:

Poll NFC-A (ISO 14443-3A) → if tag: activate
     ↓ (no tag)
Poll NFC-B (ISO 14443-3B) → if tag: activate
     ↓ (no tag)
Poll NFC-F (FeliCa) → if tag: activate
     ↓ (no tag)
Poll NFC-V (ISO 15693) → if tag: activate
     ↓ (no tag)
Wait 1 s → repeat

This sequential polling adds ~20 ms per technology to the discovery latency. Disable unused technologies via techs2Find to minimise latency.

EMVCo and Payment Applications

For payment reader applications (retail POS, transit gate), the ST25R3916 is EMVCo Level 1 certified in ST's module form (STSW-ST25R-MOD). The module includes the pre-certified antenna and a tested matching network, eliminating the need for individual device certification.

The EMVCo Level 1 test suite verifies RF waveform shape, field strength at defined distances, and protocol timing — all of which are sensitive to antenna tuning. Using a pre-certified module reduces time-to-market by 3–6 months.