MHz radio crystal and 32.768 kHz clock crystal - Technical guide
The crystal oscillator is the centrepiece of every LoRaWAN application. The right choice determines the range, reliability and energy efficiency of your end device.
This guide shows you what is important when selecting a crystal for LoRaWAN - for the 26 MHz or 32 MHz radio crystal on the transceiver and the 32,768 kHz clock crystal for the real-time clock.
LoRaWAN (Long Range Wide Area Network) utilises Semtech's LoRa® modulation technology to transmit data over long distances (up to 15 km in open field) with extremely low energy consumption. Compared to other wireless technologies such as Bluetooth, Wi-Fi or Zigbee, LoRaWAN places particularly high demands on the frequency-generating components:
Depending on the LoRa transceiver IC used, a 32 MHz or a 26 MHz oscillating crystal is required as the reference clock. The current generation of Semtech ICs (SX126x, LLCC68, LR11xx) operates at 32 MHz. Some older or alternative chipsets and certain gateway designs can use 26 MHz.
Transceiver IC | Reference frequency | Max. ESR (Rs) | Typical application |
SX1276/77/78/79 | 32 MHz | ≤ 60 Ω (recommended ≤ 40 Ω) | Legacy LoRaWAN end devices |
SX1261/62 | 32 MHz | ≤ 40 Ω | Current LoRaWAN end devices |
LLCC68 | 32 MHz | ≤ 40 Ω | Low-cost LoRaWAN Indoor |
LR1110 / LR1120 | 32 MHz | ≤ 40 Ω | Asset Tracking with GNSS |
SX1302/03 (Gateway) | 32 MHz | ≤ 40 Ω | LoRaWAN Gateways |
SX1301/SX1308 (Legacy) | 26/32 MHz | ≤ 40 Ω | Legacy LoRaWAN Gateways |
Non-Semtech modules | 26 or 32 MHz | IC-dependent | Check data sheet |
The reference frequency (26 MHz or 32 MHz) and the required load capacity are clearly specified there. Or ask us, as we have already realised many applications with Semtech ICs.
This is the key decision when selecting LoRaWAN crystals:
Crystal crystal recommended for:
TCXO recommended for:
Important: The LoRaWAN specification of the LoRa Alliance® does not prescribe TCXO.
The choice depends on the specific application.
Recommended: ±10 ppm max. for LoRaWAN end devices.
For standard LoRaWAN end devices in the temperature range from -20°C to +70°C, a temperature stability of ±10 ppm max. is sufficient, or for -40°C to +85°C a temperature stability of ±15 ppm max. is sufficient. For extended temperature ranges from -40°C to +105°C or even -40°C to 125°C, a crystal with narrow temperature stability or a TCXO is required.
The crystal ageing after 10 years is recommended with ±10ppm max.
The ESR (series resistance) of the crystal is particularly relevant for LoRaWAN applications:
Recommendation: Use oscillating crystals with ESR values well below the maximum values. Our exclusive LRT resonant crystals (Low ESR Resonator Technology) offer a significant advantage here thanks to resistance-optimised resonator designs with particularly low ESR values.
Must be matched to the IC recommendation. Common values for LoRa transceivers: 6 pF, 8 pF, 9 pF, 10 pF or 12 pF - depending on the IC and reference design. A mismatch shifts the operating frequency and can violate the overall frequency tolerance. In most applications, our LoRa crystals are used with a load capacitance of 8 pF.
| Housing size | Recommendation |
| 3.2 x 2.5 mm / 4-pad | Standard recommendation - best price-performance ratio, very low ESR values |
| 2.0 x 1.6 mm / 4-pad | If space on the board is limited - also low ESR values available and already at the same price level as the 3.2x2.5mm/4pad crystal |
| 1.6 x 1.2 mm / 4pad | For those who find the 3225 and the 2016 SMD oscillating crystal too large - low ESR values also available |
| 2.5 x 2.0 mm / 4-pad | Still available, no longer primarily recommended for new developments |
| Parameters | Specification |
| Frequency | 32,000 MHz (or 26,000 MHz - according to IC data sheet) |
| Frequency tolerance | ±10 ppm at +25 °C |
| Temperature stability | ±10 ppm (-20/+70 °C) or ±15 ppm (-40/+85 °C) |
| Load capacitance | 8 pF or 10 pF (according to IC reference design - other CL values available) |
| ESR (max.) | ≤ 40 Ω (recommended: significantly lower) |
| Housing | 3.2 x 2.5 mm / 4-pad or 2.0 x 1.6 mm / 4-pad ceramic or 1.6 x 1.2 mm / 4-pad for very small applications |
| Temperature range | -40 °C to +85 °C (or +125 °C for automotive) |
We will be happy to assist you in selecting the appropriate ceramic housing for your interpretation and realisation.
In addition to the MHz radio crystal, most LoRaWAN end devices require a 32,768 kHz clock crystal for the real time clock (RTC) of the microcontroller:
The newer Semtech transceivers LR1110 and LR1120 have an integrated 32,768 kHz low-frequency crystal oscillator (XOSC), which can be used directly for the RTC. Alternatively, an external 32,768 kHz clock can be supplied by the host microcontroller via DIO11, or a 32,768 kHz crystal with a load capacitance of 9pF can be used.
The ESR is also a key parameter for the 32.768 kHz quartz - perhaps even more critical than for the MHz quartz. Many microcontroller oscillator stages have a limited negative input resistance. If the ESR is too high, the crystal will not oscillate reliably.
| Housing | Type. ESR (max.) | Note |
| 3.2 x 1.5 mm / 2-pad | 50 kΩ | Best compromise: lowest ESR, most favourable price |
| 2.0 x 1.2 mm / 2-pad | 70 kΩ | If smaller housing required |
| 1.6 x 1.0 mm / 2-pad | 90 kΩ | Smallest housing, but highest ESR - critical |
Recommendation: For LoRaWAN applications, the 32.768 kHz crystal in a 3.2 x 1.5 mm / 2-pad ceramic housing with max. 50 kΩ ESR is the safest and most favourable choice. Its low resistance ensures faster and safer transient behaviour.
If space is tight on the board, it is often the better and more favourable strategy to switch to a smaller housing for the MHz crystal (e.g. 2.0 x 1.6 mm or even 1.6 x 1.2 mm) and to stick with the tried and tested 3.2 x 1.5 mm housing for the 32.768 kHz crystal - this is where the ESR advantage is greatest and it is easier to work with the M3215RR will not cause any transient problems.
For the RTC function, a frequency tolerance of ±20 ppm at +25 °C is sufficient in most cases. For LoRaWAN Class B synchronisation, a tighter tolerance of ±10 ppm may be advantageous.
Typical values: 4 pF, 6 pF, 7 pF, 9 pF, 12.5 pF or 18 pF. The load capacitance must be exactly matched to the MCU manufacturer's recommendation. The 32.768 kHz crystals with the standard load capacitances of 7 pF and 9 pF are usually used in LoRa WAN applications. A frequent source of error in LoRaWAN designs is the use of a 32,768 kHz crystal with the wrong load capacitance, which leads to systematic frequency shift and RTC drift.
| Parameters | Specification |
| Frequency | 32.768 kHz |
| Frequency tolerance | ±20 ppm at +25 °C (±10 ppm for Class B) |
| Load capacitance | According to MCU data sheet (e.g. 7 pF or 9 pF, other values available) |
| ESR (max.) | ≤ 50 kΩ (recommended) |
| Housing | 3.2 x 1.5 mm / 2-pad ceramic (recommended) |
| Temperature ranges | -40 °C to +85 °C, -40 °C to +105 °C or -40 °C to +125 °C |
The choice of crystal for LoRaWAN applications requires careful consideration of frequency accuracy, ESR, housing size and cost. For the MHz radio crystal, a 32 MHz (or 26 MHz, depending on the IC) oscillating crystal with low ESR (≤ 40 Ω) and ±10 ppm frequency tolerance is the right choice for most end devices. Of course we can also supply 32 MHz TCXOs can also be supplied. The most favourable version in a 2.0 x 1.6 mm ceramic housing is preferred.
For the RTC, we recommend a 32.768 kHz crystal in a 3.2 x 1.5 mm ceramic housing with a maximum ESR of 50 kΩ - the most reliable transient behaviour at the lowest price.
The decisive success factor is working with a crystal specialist who can support you in the selection process and, if necessary, carry out a circuit analysis to ensure the optimum transient response safety reserve for your specific LoRaWAN application.
Our frequency experts will be happy to advise you - contact us for a customised recommendation or use our quartz configurator for a quick product selection.
Product configurator MHz crystal oscillator 3.2 x 2.5 mm / 4-pad
Product configurator MHz oscillating quartz crystal 2.0 x 1.6 mm / 4-pad
Product configurator MHz oscillating quartz crystal 1.6 x 1.2 mm / 4-pad
Product configurator 32kHz crystal oscillator 3.2 x 1.5 mm / 2-pad
Product configurator 32kHz crystal oscillator 2.0 x 1.2 mm / 2-pad
Product configurator 32kHz crystal oscillator 1.6 x 1.0 mm / 2-pad
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