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UCC28951-Q1: Recommended Connection for unused pins

Hidekazu Someno
Expert 5130 points
Part Number: UCC28951-Q1

Hi Team,

Please tell me the recommended pin connection in the following conditions.

1. About the DELEF pin

In case synchronous rectification is not used in the application,
How should this terminal be handled?

2. About the DCM pin
In case synchronous rectification is not used in the application, It should be recommended to connect DCM to VREF.
Is it possible to connect the terminal directly to VREF in this case or , is any resister to VREF needed?

3. About the ADELEF pin

In case synchronous rectification is not used in the application,
How should the terminal be handled?  Is it sufficient to connect the terminal directly to GND?

4. About the SYNC pin.
How should the terminal be handled  when this pin is not used?

 

5. About the OUT-E, OUT-F pin

How should they be handled when these pins are not used,

Leaving open is enough, or Is any connection to GND(directly or via resister) needed?

Best regards,

Hidekazu Someno

  • 0
    TI__Mastermind 25570 points

    Hello Someno-san

    1/ The DELEF pin should be connected to GND through a 13kOhm resistor.

    2/ DCM pin; I will have to check this.

    3/ ADELEF pin: should be connected directly to GND

    4/ The SYNC pin may be left open circuit.

    5/ The OUTE and OUTF pins should be left open circuit.

    Regards
    Colin

  • 0 in reply to Colin Gillmor
    TI__Expert 5130 points
    Colin-san,

    Thanks for comments.
    Please confirm on question-2.

    Regards,
    Hidekazu Someno
  • 0 in reply to Hidekazu Someno
    TI__Mastermind 25570 points
    Hello Someno-san

    Apologies for the delay in responding.

    The DCM function may be disabled by connecting the pin directly to VREF

    Regards
    Colin
  • 0 in reply to Colin Gillmor
    TI__Mastermind 25570 points
    Hello Someno-san

    A little more on the DCM pin

    If the DCM pin is connected to GND with Diode rectification
    OUTE and OUTF signals are OFF always, from 0% load to 100% load.
    When the load current drops and the output inductor current becomes discontinuous then you get burst mode when Ton drops below Tmin in the usual way

    If the DCM is connected to VREF - with diode rectification
    OUTE and OUTF signals are always active, from 0% load to 100% load.
    The output inductor current goes discontinuous as the load current drops and the Ton starts to reduce as the load current is reduced further. Eventually the controller goes into burst mode when Ton drops below Tmin.

    If the controller is being used with SRs
    The OUTE and OUTF signals are always active and this allows the inductor current to be continuous under all load conditions. Duty cycle is therefore not a function of load current and Ton does not drop below Tmin which means you do not enter burst mode.

    Regards
    Colin
  • 0 in reply to Colin Gillmor
    TI__Expert 5130 points

    Hi Colin-san,

    In case OUTE & OUTF are not needed(Customer doean't use them in the application),   which is better to connect to VREF or to GND?

    On the datasheet(7.3.12 Dynamic SR ON/OFF Control (DCM Mode) on page 25), there is the following description. So, customer is supposing that connecting to VREF is good to shut both OUTE & OUTF off.

    ["Connecting the DCM pin to VREF makes the controller run in DCM mode and shuts both Outputs OUTE and OUTF."]

    Best regards,

    Hidekazu Someno

  • 0 in reply to Hidekazu Someno
    TI__Mastermind 25570 points

    Hello Someno-san

    You are correct. The DCM pin may be connected directly to VREF and the OUTE and OUTF signals are both shut down.

    Regards

    Colin