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TPS7H4001-SP: SYNC1, SYNC2 setting

Part Number: TPS7H4001-SP

If I want to operate the TPS76H4001 using the internal oscillator and a frequency different that 500 kHz, how should the SYNC1 and SYNC2 pins be set?

Table 7-1 in the data sheet indicates that SYNC1 should be floating, while SYNC2 is connected to GND.

Using the Pspice transient model, if I follow this recommendation and set RT to 350k ohm, the switching freq is 50 kHz. If I ground both SYNC1 and SYNC2,  the switching frequency is 250 kHz which is close to the data sheet equation.  

Maybe the model doesn't handle this condition correctly? 

  • Hi Mark,

    This is interesting.  I need to confirm what actually happens on the EVM as I just noticed that both SYNC1 and SYNC2 are left floating on the 1-CH EVM.  I am assuming grounding SYNC2 will pose no issues and the model just needs to be updated but will confirm and get back to you soon.

    Thanks

    Christian  

  • Hi Christian,

    A little more detail. The comment about the switching frequency being 50KHz when SYNC1 is floating in the model was true for running on a regular Pspice platform.  When I try to run this on Pspice for TI, the simulation won't run and marks the floating SYNC1 pin as an error. If I connect any kind of resistance to this pin, say 10Meg to emulate it being open circuit,  then the model switches at the correct frequency. 

    Speaking of models, on the AC model for the TPS7H4001, do you know what pins need to be connected to a component/circuit and which need to be grounded. It seems many device pins are not really used by the model and works in Pspice when grounded like EN, RT, REFCAP, SS_TR, SYNC1, SYNC2. I used the reference design included in Pspice for TI to get an idea of how to get the model running correctly and these signals are all grounded. Looks like the desired switching freq is set by params statements in the model. Is this correct? 

  • Hi Mark,

    I confirmed device switches at 500kHz with SYNC2 floating or grounded in hardware.  So seems the issue, as you state, is simulation driven.  What you say about avg model pins seems plausible but I am asking our modeling expert to verify.

    Thanks

    Christian

  • Hi Mark,

    Modeling expert confirmed your observations:

    "Yes, FSW is only set through the parameter called “FS”. The RT pin is unused inside the average model – as are the SYNC1, SYNC2, SS_TR, EN, REFCAP, PWRGD pins..."

    Thanks,

    Christian