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TPS50601A-SP: SYNC pin input current spec and sync circuit for 3.3V sync signal, 5V Vin&PVin

Steve Widener
Genius 11010 points
Part Number: TPS50601A-SP
Other Parts Discussed in Thread: TPS7H4002-SP

What is the maximum sync pin input current?

What is the recommended circuit to interface a 3.3V +/- 5% sync signal to the TPS50601A-SP SYNC pin in the case where Vin = PVin = 5V +/- 5%?

The datasheet calls for a 10kohm pull-down on SYNC at start-up so it is not clear that a simple transistor inverter with a pull-up will work properly & meet the Vih requirements. 

What initial start-up conditions are required for the SYNC signal?

  • 0
    TI__Genius 14540 points

    Hi Steve,

    Let me see what I can dig up.  I suspect some of this information is not available as it probably was not characterized so might have to ask design team for estimates based on simulations.  I'll get back to you soon.

    thanks

    Christian

  • 0 in reply to Christian Yots
    TI__Genius 14540 points

    For PVIN=5V operation, the external input clock should meet the min VIH requirements determined in simulation and characterization (see below).  A 3.3V clock source will meet this requirements with margin.

    The SYNC circuitry of TPS50601A-SP was reused for the TPS7H4002-SP (POL3A) which is in development.  Below are sims and measurements for the TPS7H4002-SP which apply to the TPS50601A-SP.

     The 10kohms termination on the SYNC pin is for the internal oscillator mode.  The recommended termination is actually 910ohms on the SYNC pin (as found on the EVM) when using the internal oscillator as the clock source, which is not the case described here.  This termination was found to mitigate SETs during heavy ion testing.

    Top-level simulation:

    SYNC VIH threshold @ 3V: 1.77-1.82V

    SYNC VIL threshold @ 3V: 0.88-0.9V

     

    SYNC VIH threshold @ 5V: 2.818-2.852V

    SYNC VIL threshold @ 5V: 1.34-1.366V

     

    SYNC VIH threshold @ 7V: 3.84-3.878V

    SYNC VIL threshold @ 7V: 1.76-1.8V

     

     

    Bench Validation:

    SYNC VIH threshold @ 3V: 1.64-1.76V

    SYNC VIL threshold @ 3V: 0.88-0.96V

     

    SYNC VIH threshold @ 5V: 2.64-2.8V

    SYNC VIL threshold @ 5V: 1.32-1.480V

     

    SYNC VIH threshold @ 7V: 3.6-3.8V

    SYNC VIL threshold @ 7V: 1.8-2.04V

    Thanks,

    Christian

  • 0 in reply to Christian Yots
    TI__Genius 11010 points

    Thanks Christian - this is very useful.

    Did the sims provide an estimate of the input current into the SYNC pin? That would help in sizing a pull-up resistor

  • 0 in reply to Steve Widener
    TI__Genius 14540 points

    Let me ask if that information is available- I was not given it.  Thanks, Christian

  • 0 in reply to Christian Yots
    TI__Genius 14540 points

    Feedback from designer:

    "There is an explicit 6Mohm resistor pull-down on the SYNC pin which will consume most of the input leakage current. Beyond that there is junction leakage. I simulated the input over process corners, VIN/SYNC 3V-7V, and -55C to 130C junction and get the below spread on the input leakage current:

     Min=258nA

    Max=2.4uA"

    Thanks

    Christian

  • 0 in reply to Christian Yots
    TI__Genius 11010 points

    Christian,

    Are the SYNC VIH thresholds worst-case over lot, temperature & radiation?

    SYNC VIH threshold @ 5V: 2.818-2.852V

    SYNC VIL threshold @ 5V: 1.34-1.366V

    The SYNC input is 3.3V and there are plans to add a 3.3V -> 5V translator to make sure there is margin for the SYNC Vih level. If the true Vih min is 2.852V for a 5V supply, the 3.3V -> 5V translators may not be needed.

    Likewise, does the SYNC input current max include any radiation effects? 

  • 0 in reply to Steve Widener
    TI__Genius 14540 points

    The SYNC thresholds and SYNC input current are over worse case process corners and temperature.  Radiation effects are not simulated.

    Thanks

    Christian