STW81102 datasheet(34/43 Pages) STMICROELECTRONICS

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SPI digital interface

STW81102

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6.3.1

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 is corresponding 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).

6.4

VCO calibration procedure

The calibration of the VCO center frequency is activated by a '0' to '1' transition of the

SERCAL bit (ST1 Register bit[6]).

In order to program properly the device, ensuring the VCO calibration, the following

procedure is required before every channel change:

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

Charge Pump, Prescaler Modulus) and 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 SERCAL bit set to '1'

The maximum allowed PFD frequency (fPFD) to perform the calibration process is 1 MHz; if

the desired fPFD is higher than 1MHz the following steps are needed:

–

Perform all the steps of the calibration procedure programming the desired VCO

frequency with a proper setting of R, B and A counter so that fPFD is ≤ 1MHz.

–

Program the device with the proper setting for the desired VCO and PFD

frequencies according to the above step a) and b) only.

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