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ADC16DX370 : Use of SYNC functionality

Other Parts Discussed in Thread: ADC16DX370

Hi,

We are using ADC16DX370 in our design. For this IC, whether SYNC+ and SYNC- signals are compulsorily to be routed as differential? Can we use only SYNC+ as a single ended signal, connecting SYNC- to ground? 

Why this question raised because we have an ADC card as a daughter card getting connected to a General Master card. There are 2 separate single ended signals getting connected from master card to SYNC pins of ADC. So with this existing connection, can we implement the SYNC functionality for ADC?

Hope I made my question clear. Experts, please suggest.

Regards,

Vijetha

  • Hi Vijetha,

    The differential SYNCb+/- input of the ADC16DX370 has a wide input common-mode range, so driving it with a single ended signal is possible, but not entirely straight forward due to the internal 100ohm termination between SYNCb+ and SYNCb-. If you want to drive the SYNCb+ single-ended, then the SYNCb- pin must be connected to voltage bias that can source and sink a sufficient amount of current. Ideally, SYNCb- would be biased around mid-scale. These conditions should be satisfied:

    1) The input common-mode must stay between 0.5 and 2.0V

    2) The achieved differential input swing should achieve at least +/-100mV

    3) The voltages on SYNCb+ should not exceed the absmax condition (and should have some margin)

    4) Put a good decoupling cap on the SYNCb- input so that it can provide current with reasonable speed

    A key point here is that, to generate +/-100mV across the inputs with the internal 100 ohm termination, +/-1mA must flow through the termination, therefore the bias on SYNCb- must sink/source that much current without significantly changing voltage and while still maintaining the common-mode range. The single-ended driver must also be able to sink/source that much current.

    So here is an example implementation: Supply a single-ended 1.8V CMOS signal to SYNCb+. Bias SYNCb- at 1.0V with a bias that has 100ohm output impedance (or less). In this example, the common-mode varies from 0.5V to 1.6V and the differential swing is +400/-500mV.

    Regards, Josh 

  • Thank You sir for the reply.

    We will try to implement above points. If I come across further queries I will post again.

    Regards,

    Vijetha