Hi! all,
My cutermer has some questions as below;
1.In case of AC termination of LVDS output of LMK04826,
the circuit diagram of LMK04826 user's guide shows that there is a 560-ohm termination at the transmission
side as below image.
My understanding is that 560-ohm termination register is not required.
Does LMK04826 need 560-ohm termination register?
2. If yes, why is the 560-ohm termination register needed?
LMK04826 needs DC loop?
3. When costomer set the register below steps, there are some different result.
Case 1: There is no 560-ohm at transmission side.
Set SYSREF output powerdown to REG 0x107 & REG 0x10F
Select SYSREF multiplex to SYSREF Continuous (0x03) ; REG 0x139
Set SYSREF_CLR=0 to REG 0x143
Set SDCLKoutY_FMT=0x01 to REG 0x107 & 0x10F ; LVDS output enable
Result: LMK04826 can generate CLOCK corectlly.
Case 2: There is no 560-ohm.
Set SDCLKoutY_FMT=0x01 to REG 0x107 & 0x10F ; LVDS output enable
Select SYSREF multiplex to SYSREF Continuous (0x03) ; REG 0x139
Set SYSREF_CLR=0 to REG 0x143
Result: LMK04826 can not output CLOCK.
Case 3: There is 560-ohm.
Set SDCLKoutY_FMT=0x01 to REG 0x107 & 0x10F ; LVDS output enable
Select SYSREF multiplex to SYSREF Continuous (0x03) ; REG 0x139
Set SYSREF_CLR=0 to REG 0x143
Result: LMK04826 can output CLOCK.
Why are there the diffrent results by the above cases?
Is there any recommendation of programing step?
Regards,
Toshi
