ADS4149: CMOS CLKOUT STRENGTH

Irmak Ece Sener Yalcin

Part Number: ADS4149

Based on the IBIS model of ADS4149, we decided to use the CMOS_DATA_HIGH1 buffer.

How should we set the register bits (in the address 41h) in order to use the CMOS_DATA_HIGH1 buffer settings? Does this correspond to CMOS CLKOUT STRENGTH BITS: 00 = Max strength?

over 3 years ago

+1 jim s over 3 years ago

TI__Guru* 91947 points

Irmak,

Yes, 00 = max strength.

Regards,

Jim

0 Irmak Ece Sener Yalcin over 3 years ago in reply to jim s

Prodigy 70 points

The IBIS Model of ADS4149 uses the CMOS_DATA_HIGH1 buffer for all these outputs:

OVR_SDOUT

CLKOUTP

D0_D1_P

D0_D1_M

Does this mean if we set the 00 = max_strength, are they all set to the max strenght or is it only for clock?

If it is only for clock, how can we arrange the strengths for D0_D1_P, D0_D1_M and OVR_SDOUT?

+1 jim s over 3 years ago in reply to Irmak Ece Sener Yalcin

TI__Guru* 91947 points

Irmak,

CMOS max strength applies to CMOS Clock only. Since the clock is the fastest toggling signal, extra strength on clock output helps reduce rise/fall time and therefore improves output timing.

CMOS timing numbers specified in datasheet are taken with this mode only, and by default after reset the CMOS buffer is programmed to max strength.

In some cases, based on how CMOS outputs are routed on board, there may be a possibility for output clock coupling to analog inputs and degrading performance especially noise and spurs.

In such cases, customer may try to reduce the strength of CMOS output clock buffer and see if performance improves.

Regards,

Jim

0 Irmak Ece Sener Yalcin over 3 years ago in reply to jim s

Prodigy 70 points

Jim,

Thank you for your answer. I have one more question:

Is there a possibility that we can drive the data outputs in high drive strength and set the clock drive strength to low? If yes, how can we arrange that?

Regards

Irmak

0 jim s over 3 years ago in reply to Irmak Ece Sener Yalcin

TI__Guru* 91947 points

This is not possible.

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ADS4149: CMOS CLKOUT STRENGTH