CDCM6208: Vcm_DC 's Value

Harry Ma

Part Number: CDCM6208

Hi Team

Customer plan to use DC coupled output mode. In EC table, is the VDD_Yx_Yy -0.76 typical value? and if they choose VDD_Yx_Yy=3.3, so Vcm_DC=2.54V?

Thanks!

over 3 years ago

0 Julian Hagedorn over 3 years ago

TI__Mastermind 20900 points

Hello,

the output stages of CDCM6208 are CML drivers. This is a VDD referenced output type. For LVDS (Low-power CML) the output swing is adjusted. If you do DC coupling the VCM will be VDD_Yx_Yy - 0.13V. At 3.3V this results in VCM_DC = 3.17V typ.

It is recommended to do AC coupling with CDCM6208.

regards,

Julian

0 user6280143 over 3 years ago in reply to Julian Hagedorn

Prodigy 30 points

Hi Julian,

Our project used CDCM6208 and 3 outputs of CDCM6208 are configured as lvds output.The VDD_Yx_Yy is 3V3.I measured the three lvds output whose VCM_DC are around 1.0v ,not 3.17V.And 1.0V VCM meets the LVDS standards.So Is there anything misunderstanding about the VDD_Yx_Yy-0.13 in
CDCM6208 datasheet?

Thanks!

0 Julian Hagedorn over 3 years ago in reply to user6280143

TI__Mastermind 20900 points

Hello,

have you measured the common mode at the receiving device after the AC coupling cap?

If measured DC coupled, was the receiving device connected? If yes, what is the input structure? Does it has an internal biasing circuit?

Regards,

Julian

0 user6280143 over 3 years ago in reply to Julian Hagedorn

Prodigy 30 points

Hi Julian

I misunderstood the Vcm_DC and VCM_AC.3 lvds outputs are ac coupled,and one of them connects no received device.The VDD_Yx_Yy is 1v8.And I measured the cdcm6208 side ,the VCM is about 1v0.,Sorry about providing the wrong message.

Regards

0 Julian Hagedorn over 3 years ago in reply to user6280143

TI__Mastermind 20900 points

Hello,

ok with VDD_Yx_Yy = 1.8V and AC coupling the common mode at the CDCM6208 side is around 1V (VDD_Yx_Yy - 0.76V typically).

With AC coupling that does not matter however. You will need to ensure that the receiver has a biasing circuit internal or external.

regards,

Julian

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CDCM6208: Vcm_DC 's Value