PllLdr is a generic microcontroller to load a PLL chip’s configuration registers using SPI. SPI is used by many PLL and DDS chips, data format and content varies from chip to chip.
This article documents checkout on an ADF4351 PLL chip. The ADF4351 is a wideband INT-N / FRAC-N synthesiser with integrated VCO, output covers 36-4400MHz (continuous).
The test was made on an inexpensive module purchased on eBay for about A$33 posted.

Above is the test frame. At the left is a PllLdr prototype running on 5V, then a 4 channel 5V/3.3V level converter, the ADF4351 module and at the right a power supply board. The level converter is not needed if the PllLdr chip was run on 3.3V, it was used to test a ‘worst case’ scenario.

Above, a close up of the board.

As can be seen, the connectors are not designed for the 0.8mm PCB used, and the right hand connector has not been connected to the track. Chinese ‘quality’.
The onboard 25MHz crystal oscillator was used as the reference, but a 10MHz reference from a GPSDO could be used for high accuracy. Continue reading ADF4351 / PllLdr checkout
Last update: 15th September, 2016, 11:52 AM