LMX2571EVM: PLL can not be locked

Hi Peter,

Did you program all registers? in the menu bar, click USB Communications --> Write All Registers.

Check to see if the SPI communication is all right. Program below register will has noticeable current change.

- Program POWERDOWN = 1

- Set TX Enable, RX Enable = 1 or 0.

Hi Noel

1.SPI communication is fine by test result as below

Program POWERDOWN=1/0 CURR= 3.02mA /5.12mA

OUTBUF_TX_EN_F1=1, OUTBUF_RX_EN_F1=1/0 CURR=5.12/4.39mA

OUTBUF_RX_EN_F1=0, OUTBUF_TX_EN_F1=1/0 CURR=5.23/4.43mA

2.Waveform of F_OSC, F_IN is as below

3.At now TP_CPout_Ext=2.2V

4.Remove F_OSC, 

TP_CPout_Ext=1.98V

5.PLL LED is still not shown locked

BRs

Peter Hsiao

Hi Peter,

Is the F_osc single-ended or differential? Do you have external termination at OSCin? 

set IPBUF_SE_DEFF_SEL according to your input format. If there is no external termination, enable IPBUFDIFF_TERM bit.

Hi Noel

1."Is the F_osc single-ended or differential? Do you have external termination at OSCin?" [Peter] Yes, it is SE with a external termination.

2.After removing components of  loop filter as below 1,2,3,4,5 , PLL is locked .

3.What is the current should be provided by the 5V adapter? Is it 1A enough ?

BRs

Peter Hsiao

Hi Peter,

Current consumption of the LMX2571 in PLL mode is about 10mA.