STW81101AT datasheet(37/48 Pages) STMICROELECTRONICS

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STW81101

SPI digital interface

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7.3.1

Default configuration

At power on reset, the following configuration is automatically loaded:

–

FUNCTIONAL MODE = 1 (VCOA with divided by 2 output)

–

A COUNTER = 8

–

B COUNTER = 562

–

R DIVIDER = 192

–

PLL_A[1:0] = [10]

–

CP_SEL[2:0] = [111]

–

PSC_MOD_SEL set to 0 (Modulus = 16)

This corresponds to an output frequency of 1800MHz and a PFD frequency of 400kHz using

a 76.8MHz reference clock (calibration algorithm of the VCO is automatically started).

7.4

VCO calibration procedure

Calibration of the VCO center frequency is activated by a transition of the SERCAL bit (ST1

To program the device properly while ensuring VCO calibration, perform the following steps

before every channel change:

Program the ST1 register with the desired settings (R counter, VCO amplitude, charge

pump, prescaler modulus) and with the SERCAL bit set to 0.

Program the ST2 register with the desired settings (functional mode, B and A

counters).

Program the ST1 register with the desired settings (R counter, VCO amplitude, charge

pump, prescaler modulus) and with the SERCAL bit set to 1.

The maximum allowed PFD frequency (FPFD) during calibration is 1 MHz; if you want a

FPFD higher than 1MHz, perform the following additional steps:

Perform all the steps of the calibration procedure, making sure to program the

desired VCO frequency with proper settings of the R, B and A counters so that

FPFD is ≤1MHz.

Program the device with the desired VCO and PFD frequency settings using only

steps 1) and 2) above.

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