Lierda FP20 Series LoRa Modules: 868/915MHz SPI Passive Crystal Modules
The FP20 series offers cost-effective LoRa modules based on Semtech's SX126X chip, featuring an SPI interface. These modules support configurable transmission power up to 22.5 dBm and utilize an internal TCXO crystal oscillator for stable operation across a wide temperature range, ensuring low temperature influence and high precision. The FP20 series modules are characterized by low power consumption, long transmission distance, and strong anti-interference capabilities, making them suitable for applications requiring high transmission rates and extended range, such as smart home, security monitoring, smart communities, logistics, warehousing, and industrial control.
Product Features
- Operating Frequency Band: 863-870MHz (EU), 902-928MHz (USA)
- Multiple Modulation Options: Supports LoRa, GFSK, FSK, and other modulation modes.
- Ultra-low Power Consumption:
- Power supply: 1.8 V to 3.7 V (transmit power cannot be lower than 3.1 V at +22 dBm configuration)
- Transmit current: ≤ 125 mA (maximum transmit power configuration)
- Receive current: ≤ 7 mA (DC-DC mode)
- Standby current: 600 µA
- Sleep current: 1 µA (register value saved)
- High Link Budget:
- Sensitivity: -124 dBm (typical value)
- Transmit power: Max. 22.5 dBm
- Communication Interface: SPI communication interface, directly connectable to various microcontrollers for convenient software programming.
Applicable Scenarios
- Smart Home
- Security monitoring
- Low-power sensors
- Wireless remote control
- Logistics and warehousing
- Industrial control
- Applications requiring long communication distances
Lierda Technology Group Co., Ltd. provides this document to support customer product design. Customers are responsible for designing products according to the specifications and parameters provided. Lierda is not liable for personal injury or property damage due to improper customer operation. Lierda reserves the right to update this document without notice. Copyright © Lierda Science & Technology Group Co., Ltd.
1 Specification
Table 1 Module Limit Parameters
| Main Parameters | Performance | Remarks | |
|---|---|---|---|
| Minimum Value | Maximum Value | ||
| Supply voltage (V) | -0.5 | +3.9 | |
| Maximum RF input power (dBm) | - | +10 | |
| Operating temperature (°C) | -40 | +85 | |
Table 2 Module Operating Parameters
| Main Parameters | Module Type: L-LRMFP20-97NN4 | Remarks |
|---|---|---|
| Operating voltage (V) | 1.8 ~ 3.7 | VBAT ≥ 3.1 V for +22 dBm VBAT ≥ 2.7 V for +20 dBm VBAT ≥ 2.4 V for +19 dBm |
| Operating temperature (°C) | -40 ~ 85 | |
| Operating Frequency Band (MHz) | 860 ~ 930 | User programmable customization¹ |
| Initial frequency offset (kHz) | -3 ~ +3 | Factory deviation |
| Emission current (mA) | Vmin=100 Vtype=125 | DC-DC mode, 22dBm emission² |
| Receiving current (mA) | Vmax=135 Vtype=6.5 Vmax=7.5 | DC-DC mode, Rx Boosted BW_L=125KHz, SF=7 |
| Sleep current (µA) | Vtype=1 Vmax=3 | Register value saving |
| Transmit power (dBm) | Vmin=20.5 Vtype=21.5 Vmax=22.5 | 22dBm emission, user programmable customization |
| Reception sensitivity (dBm) | Vtype=-124 | SF 7_BW 125KHz |
| Communication protocols | SPI | |
| Interface type | Stamp hole | 2mm spacing |
| Dimensions (mm) | 18.4 × 18.4 × 3.0 | |
| Dimensional accuracy | GB/T1804-C 级 | Meet the dimensional tolerance class C requirements |
¹ Users are allowed to configure and use the working frequency band according to local regulations. Please comply with local regulations. Lierda is not responsible for non-compliance.
² Output power must be set according to recommended values to avoid performance degradation or damage.
2 Dimensioning and Pin Definition
2.1 Dimensional Drawings
Figure 1 shows the dimensions of the FP20 series module. The module measures 18.4 x 18.4 x 3.0 mm, with a 2.0 mm pitch for the stamp hole interface.
2.2 Hardware Block Diagram
Figure 2 illustrates the hardware system block diagram. The core component is the SX126X chip, connected to a crystal oscillator, SPI interface, functional pins (NRESET, DIO1, BUSY), and an RF interface via a matching network and SPDT switch.
2.3 Pin Definitions
2.3.1 Power Supply
| Interface Name | Pin Serial Number | Direction | Description |
|---|---|---|---|
| VDD | 8 | Power Supply | Power supply VDD |
| GND | 7, 13 | Power Supply | Power supply ground |
2.3.2 SPI Communication Interface
| Interface Name | Pin Serial Number | Direction | Description |
|---|---|---|---|
| MISO | 9 | Output | SPI data output |
| MOSI | 10 | Input | SPI data input |
| NSS | 11 | Input | SPI chip select |
| SCK | 12 | Input | SPI clock input |
2.3.3 Functional Interface
| Interface Name | Pin Serial Number | Direction | Description |
|---|---|---|---|
| NREST | 1 | Input | Reset pin, active low |
| DIO1 | 2 | Output | Interrupt source mapping pin |
| BUSY | 3 | Output | Busy indicator |
| NC | 4, 5, 6 | No connect (do not connect to GND) |
2.3.4 RF Interface
| Interface Name | Pin Serial Number | Direction | Description |
|---|---|---|---|
| RF | 14 | Input/Output | RF input/output |
3 Basic Operation
3.1 Typical Application Circuit
Figure 3 shows a typical application circuit. DIO1 can be used for all interrupt mapping functions. The internal RF switch is controlled by DIO2. Table 7 provides the control logic for DIO2 as an RF switch control.
Table 7 Control Logic Truth Tables
| MODE | DIO2 |
|---|---|
| Transmit | 1 |
| Receive | 0 |
| Sleep | 0 |
The function `SX126xSetDio2AsRfSwitchCtrl(uint8_t enable)` controls the RF switch mode.
3.2 Hardware Layout Recommendations
- Connect DIO ports to MCU IO ports with external interrupts where possible.
- Keep the RF cable between the RF outlet and the antenna solder pad as short as possible, using 50-ohm impedance lines with ground shielding. Drill holes around the cable.
- Add a π circuit to the RF outlet portion of the antenna pad if space permits.
- Ensure a clearance area of at least 5 mm around the antenna.
- Ensure good grounding with a large ground plane.
- Keep away from high voltage and high frequency switching circuits.
- Refer to RF PCB LAYOUT Design Rules for sub-1GHz and Bluetooth Modules for detailed layout guidance.
3.3 Software Operation
This module operates as a slave device with an SPI interface. Users can communicate with it via the MCU's SPI interface, controlling its registers and transceiver cache through API instructions to achieve wireless data transmission. Users need to adapt the SPI operation to their specific MCU. For timing operations of module register read/write, refer to the latest SX1262/8 datasheet. It is recommended to consult Lierda's LoRa communication routines and example code for point-to-point communication to understand software operations. When porting code, tune the SPI interface for your MCU and transplant relevant functions from the communication routines.
Figure 4 illustrates the point-to-point communication process using a pair of LoRa modules, where a transmitting device sends data to a receiving device, which then returns the data packet for circular communication.
3.4 I/O Port Level in Sleep Mode
Table 8 details the I/O port levels in sleep mode:
Table 8 I/O Port Level in Sleep Mode
| DIO1 | BUSY | MISO | MOSI | SCK | NSS | NRESET |
|---|---|---|---|---|---|---|
| HIZ PD³ | HIZ PU⁴ | HIZ⁵ | HIZ | HIZ | IN⁶ | IN PU |
³ PD = pull down with 50kΩ.
⁴ PU = pull up with 50kΩ.
⁵ HIZ = High Impedance State.
⁶ IN = Input.
3.5 Transmit Power Configuration
Different product models have different matching networks and PA settings. It is crucial to configure transmit power strictly according to the corresponding product specifications to avoid performance issues or damage. Transmit power can be configured by setting the `SetTxParams` register or by simultaneously configuring `paDutyCycle`, `hpMax`, `deviceSel`, and `paLut` register values.
3.6 Disable Frequency Point Description
Disabled frequency points indicate frequencies where module performance is very poor and should not be used. Not recommended frequency points indicate frequencies with poor performance; users may use them cautiously. It is recommended to use frequencies at least 1 MHz away from disabled frequencies.
- Disabled frequencies: 864 MHz, 896 MHz
- Not recommended frequencies: 880 MHz, 912 MHz, 928 MHz
4 Frequently Asked Questions
4.1 Modules Cannot Communicate Even at Close Range
- Check for inconsistent configurations between sending and receiving sides.
- Verify voltage levels; low voltage can cause abnormal transmission.
- Ensure sufficient battery power, as low battery can reduce voltage during transmission.
- Check antenna welding and the π circuit for proper connection.
4.2 Module Power Consumption Anomaly
- Module damage due to static electricity can cause abnormal power consumption.
- Incorrect timing configuration when receiving low power can lead to unexpected power consumption.
- In coupled systems, MCU pin configuration related to the RF module can cause abnormal power consumption.
- Harsh environmental conditions (high temperature, humidity, low temperature) can cause power consumption fluctuations.
4.3 Insufficient Module Communication Distance
- Poor antenna impedance matching can result in low transmitted power.
- Metal objects near the antenna or module can cause signal attenuation.
- Interference signals in the test environment can reduce communication distance.
- Insufficient power supply may lead to abnormal transmit power.
- Harsh test environments can cause significant signal attenuation.
- Signal attenuation and diffraction occur when communicating through walls.
- Modules placed too close to the ground can experience signal absorption and reflection.
FCC Statement: Maintain a distance of 20 cm from the body during product use to comply with RF exposure requirements. This device complies with Part 15 of the FCC Rules. Operation is subject to two conditions: (1) this device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation. The manufacturer is not responsible for radio or TV interference caused by unauthorized modifications.
Original Equipment Manufacturer (OEM) Notes
OEMs must certify the final end product for compliance with unintentional radiators (FCC Sections 15.107 and 15.109) before declaring Part 15 compliance. Integration into devices connected to AC lines requires a Class II Permissive Change. OEMs must adhere to FCC labeling requirements. If the module's label is not visible after installation, an external label stating "Contains transmitter module FCC ID: 2AOFDFP20-C8" must be applied to the finished product. The user manual must also include: "This device complies with Part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation."
The module is approved for installation in mobile and portable applications. It can be used without additional authorization if tested under the same intended end-use conditions, including simultaneous transmission. If not tested and granted in this manner, additional testing and/or FCC application filing may be required. Options for host manufacturers include submitting a permissive change application or addressing additional testing conditions such as RF exposure compliance (MPE or SAR), limited/split modules, or simultaneous transmissions for independent collocated transmitters not previously granted together.
This module has full modular approval and is limited to OEM installation only. Integration into devices connected to AC lines requires a Class II Permissive Change. The OEM integrator must ensure the entire end product complies with all regulations, including additional measurements (15B) and authorizations (e.g., Verification) if necessary due to co-location or other factors.
