LLCC68 datasheet(56/111 Pages) SEMTECH

56 / 111 page

LLCC68

Data Sheet

Rev. 1.1

DS.LLCC68.W.APP

Dec 2024

56 of 111

Semtech

LLCC68

www.semtech.com

9.2.1 Image Calibration for Specific Frequency Bands

Image calibration is done through the command CalibrateImage(...) for a given range of frequencies defined by the parameters freq1

and freq2. Once performed, the calibration is valid for all frequencies between the two extremes used as parameters. Typically, the user

can select the parameters freq1 and freq2 to cover any specific ISM band.

In case of POR or when the device is recovering from Sleep mode in cold start mode, the image calibration is performed as part of the initial

calibration process and for optimal image rejection in the band 902 - 928MHz. However at this stage the internal state machine has no

information whether an XTAL or a TCXO is fitted. When the 32MHz clock is coming from a TCXO, the calibration fails and the user should

request a complete calibration after calling the function SetDIO3AsTcxoCtrl(...).

By default, the image calibration is made in the band 902 - 928MHz. Nevertheless, it is possible to request the device to perform a new

image calibration at other frequencies. For other frequency bands, a new function is available to setup the frequency using the parameters

floor and ceil frequency in MHz. This is located in the SX126x drivers sx126x.c file:

sx126x_status_t sx126x_cal_img_in_mhz( const void* context, const uint16_t freq1_in_mhz, const uint16_t

freq2_in_mhz )

The pseudo-code is written hereafter:

#define SX126X_IMAGE_CALIBRATION_STEP_IN_MHZ 4

sx126x_status_t sx126x_cal_img_in_mhz( const void* context, const uint16_t freq1_in_mhz, const uint16_t

freq2_in_mhz )

{

// Perform a floor() to get a value for freq1 corresponding to a frequency < or = freq1_in_mhz

const uint8_t freq1 = freq1_in_mhz / SX126X_IMAGE_CALIBRATION_STEP_IN_MHZ;

// Perform a ceil() to get a value for freq2 corresponding to a frequency > or = freq2_in_mhz

const uint8_t freq2 = ( freq2_in_mhz + SX126X_IMAGE_CALIBRATION_STEP_IN_MHZ - 1 ) /

SX126X_IMAGE_CALIBRATION_STEP_IN_MHZ;

return sx126x_cal_img( context, freq1, freq2 );

}

9.3 Sleep Mode

In this mode, most of the radio internal blocks are powered down or in low power mode and optionally the RC64k clock and the timer are

running. The chip may enter this mode from STDBY_RC and can leave the SLEEP mode if one of the following events occurs:

• NSS pin goes low in any case

• RTC timer generates an End-Of-Count (corresponding to Listen mode)

When the radio is in Sleep mode, the BUSY pin is held high.

Table 9-2: Image Calibration Over the ISM Bands

Frequency Band [MHz]

Freq1

Freq2

430 - 440

0x6B

0x6F

470 - 510

0x75

0x81

779 - 787

0xC1

0xC5

863 - 870

0xD7

0xDB

902 - 928

0xE1 (default)

0xE9 (default)

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