DAC37J84: LVDS driving SYSREF input

david royle

Intellectual 575 points

Part Number: DAC37J84

Tool/software:

Datasheet indicates SYSREF differential input peak to peak voltage (VIDPP) is 0.4V.

This would indicate that Vpp is 0.2V and thus should be compatible with LVDS Vpp of 350mV.

We should be able to AC couple LVDS directly to SYSREF input, is this correct?

8 months ago

0 Kang Hsia 8 months ago

TI__Guru* 79454 points

Hello David,

Please see the following app note regarding AC coupled approach of SYSREF. Please ensure that the VCM is maintained before the SYSREF on/off

https://www.ti.com/lit/an/slaa696/slaa696.pdf

0 david royle 8 months ago in reply to Kang Hsia

Intellectual 575 points

Kang,

The datasheet indicates differential input peak to peak voltage (VIDPP) is 0.4V.

Oddly the appnote says "Based on the DAC3xJ8x datasheet, the minimum swing for each leg is 400 mVpp".

The differential p-p and swing is twice the swing of each leg.

Should I assume VIDPP=0.8V?

0 Rob Reeder 8 months ago in reply to david royle

TI__Mastermind 41760 points

Hi David,

Typical spec for Sysref is 800mVpp DIFF per the DAC datasheet.

The min spec for Sysref is 400mVpp DIFF per the DAC datasheet.

I would advise to use these numbers, not the app note, this must be an error.

Regards,

Rob

0 david royle 8 months ago in reply to Rob Reeder

Intellectual 575 points

I am trying to determine if I can AC couple LVDS.

By the datasheet the part needs typical 400mV swing each leg (=800mVpp DIFF), and and minimum 200mV swing each leg (=400mVpp DIFF). So 320mV LVDS swing each leg should be ok yes?

+1 Rob Reeder 8 months ago in reply to david royle

TI__Mastermind 41760 points

Hi David,

Yes, that should be fine.

You can AC couple the LVDS. But you need to have a 100ohm diff term at the RX side, before the 0.1uF caps.

Regards,

Rob

Data converters

Data converters forum

DAC37J84: LVDS driving SYSREF input