DAC38J84: NCO Reset via external Signal on Sysref Pin

Pavan

Part Number: DAC38J84

I our Custom Board, we are using Multiple DAC38J84. We need to reset the NCO in all the DACs at the same instant to synchronize all the DACs

1.We need alignment of DAC NCO.To do this we are doing NCO reset on Sysref. But we are unable to achieve it at 600 MHz NCO Frequency.

We are giving reset pulse to SYNC pin of LMK. From LMK we are routing this reset signal on to LMK Sysref Path. From this Path we are using this pulse to reset NCO.

Will there be any delay between the Sysref paths of two LMKs ??

Please check the NCO configurations attached for 600 MHz Output.

Fullscreen NCO_1900.txt Download

dac_write 0x2f 0x0001 dac_write 0x30 0x7fff dac_write 0x0D 0x0400 dac_write 0x02 0x20C2 dac_write 0x02 0x20D2 dac_write 0x12 0x0000 dac_write 0x13 0x0000 dac_write 0x14 0xE50D dac_write 0x15 0x9435 dac_write 0x16 0x50D7 dac_write 0x17 0xE50D dac_write 0x18 0x9435 dac_write 0x19 0x50D7 dac_write 0x1F 0x2220

2. To Align NCO Data and JESD Data, is it required to align MIxer AB and Mixer CD on all the DACs ??

Is it required to reset Mixers before NCO accumulator ?? or all NCO accu, Mixer AB, Mixer CD can be resetted at the same time, using same pulse

over 4 years ago

0 jim s over 4 years ago

TI__Guru* 91947 points

Pavan,

See section 5.1 and figure 6 of the Device Initialization document for more information regarding syncing the NCO's. The mixers must be reset before the NCO accumulator.

Regards,

Jim

Device Initialization and SYSREF Configuration.pdf 8816.Multi-Sync DAC TI Design_Multi_LMK.pdf

0 Pavan over 4 years ago in reply to jim s

Intellectual 720 points

Hi Jim

After Rising Edge of Sysref, how much time it will take to Reset DAC NCO ???

My DAC Clk = 1900 MHz

DAC Output = 100 MHZ

0 jim s over 4 years ago in reply to Pavan

TI__Guru* 91947 points

Pavan,

We are looking into this. I am assuming both the mixer and NCO are using the SYSREF as the SYNC source.

Regards,

Jim

0 jim s over 4 years ago in reply to jim s

TI__Guru* 91947 points

Pavan,

The delay is around 250ns. See attached.

Regards,

Jim

0 Pavan over 4 years ago in reply to jim s

Intellectual 720 points

Hi Jim

Is there any formula to calculate this time theoretically ??

On what parameters this time depends ?

0 jim s over 4 years ago in reply to Pavan

TI__Guru* 91947 points

Pavan,

The delay between SYSREF and NCO resync is dependent on the JESD frequency and the interpolation. Since there is clock handoffs that need to happen, this is delay different for different setups. There is no formula I know of.

Regards,

Jim

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DAC38J84: NCO Reset via external Signal on Sysref Pin