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ADF4150 charge pump current!

Question asked by medooo on Jun 10, 2013
Latest reply on Jun 17, 2013 by Grzegorz.Wawrzola

We are using ADF4150BCPZ (part number adf4150 #1121 31984)

We want to control charge pump current value. In order to do this we write value "10007F82" to the Register2. Then we update the chip with the Register0 changing. We detect the current changing by the phase noise characteristics of the output. ADIsimPLL says that the phase noise have to be changed versus the charge pump current changing. But it doesn't happen. We don't see the phase noise change versus charge pump current changing in Register2. But when we had rewritten other bits of Register2 (muxout and R divider) and they affected on the phase noise characteristics.

The replacement of Rset (from 5.1kOhm to 3kOhm) reduces the phase noise, that totally agrees with ADIsimPLL modeling results. But the recommended minimum value of Rset doesn't allow to make necessary current to reduce phase noise.

Here are the words (step-by-step) which are sent to chip during initialization.


word = 0x00400005


word = 0x00800004


word = 0x0064000B


word = 0x10007F82


word = 0x00008011


word = 0x00128000


  This chip (adf4150) doesn't allow to read the sent bits, so we can define the charge pump current changing only with the help of phase noise measurement. Is there any other way to detect the current changes?