SX1257 PMOD

This is a PMOD built around the SX1257 tranceiver. It uses an I2C-SPI bridge (SC18IS602B) since only 8 io pins are used.

RevA Pin-out:

• 1: I2C SCL
• 2: I2C SDA
• 3: CLK_IN (32 or 36 MHz)
• 4: CLK_OUT (36 MHz)
• 5: I_IN
• 6: Q_IN
• 7: Q_OUT
• 8: I_OUT

RevA errata

• Change crystal footprint.
• Add 2k pull-ups on i2c scl and sda.
• Maybe swap pin 7 and 8, makese sense to keep in and out symmetric.

RevB

RevB Pin-out:

• 1: I_IN
• 2: Q_IN
• 3: Q_OUT
• 4: I_OUT
• 5: I2C SCL
• 6: I2C SDA
• 7: CLK_IN (32 or 36 MHz)
• 8: CLK_OUT (36 MHz)

RevB errata

The pins VR_PA, VR_DIG, VR_ANA1 and VR_ANA2 should not be tied to VBAT/VCC, which they are. These are pins for decoupling for the internal voltage regulators, i.e. they should only be connected to single decoupling capacitors as stated in the datasheet.

• VR_PA: 10nF
• VR_DIG: 100nF
• VR_ANA1: 100nF
• VR_ANA2: 100nF

RX performance is poor. Why? Maybe related to the above, or bad matching circuit?

In the build of 10 units, 2 failed completely and 2 had very bad RX performance. Maybe related to the issue above.

Changes for RevC / TODO:

• Fix SX1257 Vreg decoupling issue
• Change to 0402 components
• Add optional SI514 I2C-programmable oscillator (it’s WIP on the branch si514)