ST25R NFC Reader IC Guide

ST25R NFC Reader IC Guide: STMicroelectronics

STMicroelectronics' ST25R series are high-performance NFC reader ICs targeting industrial, medical, and multi-protocol applications. Unlike NXP's PN532/PN7150 which target consumer NFC, the ST25R chips excel at extended read range, multi-protocol support (HF RFID + NFC), and precise RF control.

ST25R Family Overview

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

ST25R3916 Specifications

Why Choose ST25R Over PN532?

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:

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 NFC antenna geometry for performance requirements" data-category="Manufacturing">antenna design 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.

See Also

Use the Chip Selector to compare the ST25R3916 against other reader ICs, and the Read Range Estimator to model the range improvement from the ST25R's higher output power.

• PN532 Complete Guide
• PN7150 NFC Controller Guide
• NFC Antenna Matching Guide
• NFC Reader Firmware Development
• NFC Payments: How It Works