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UCC28950: Slave Mode in UCC28950 without Master Controller

Sudheendra Varna
Prodigy 70 points
Part Number: UCC28950

Slave Mode in UCC28950

Dear Sir/Madam

We have used UCC28950 Controller in an X-Ray Apparatus. The Load to the Power Converter can vary from 10W to ~40 kW. Power Inverter is Series Resonant Converter (With External L and C) with High Reflected Capacitance from High Voltage Transformer, In other words the converter operates in Series-Parallel Mode.

Since the reflected Load vary in a large range, it is quite difficult to operate in only in phase shifting mode. This many days we have Fixed Frequency steps By Connecting Resistor in parallel to Rt as shown below. That is Controller in master mode.

Now we wish to change the frequency in continuously (Say from 90 kHz to 150 kHz Along with phase shift modulation), By Changing the current flowing in Rt. But in Master Mode it is Difficult to change the current since the Rt is connected Vref.

In Slave mode by connecting the Rt to Gnd, Current through Rt can be varied easily configuring opamp in constant current mode.

Is it possible to operate the controller in Slave mode without a master controller? May be by connecting 825k Across SS pin to Gnd or Some Other Way, Please suggest. Please refer to Attached Doc for details.

Best Regards

B.Sudheendra Varna

Principal EngineerUCC28950_SLAVE MODE.pdf

Skanray technologies

Mysore-INDIA

  • 0
    TI__Guru* 86266 points

    Hello,

    I read through the data sheet and I am not if this device will work setup in slave mode without a sync signal.

     

    When you connect RT to GND you are setting the device up to run in slave mode.  This also sets the SYNC pin as an input.

    Equation 11 programs the default switching frequency when the sync signal is not present.  So it might work.

    Figure 43 and 44 show the sync signal is 2X as fast as the A B outputs.  There is a note that the sync frequency needs to be 1.8 times the converter switching frequency.  When I have done sync circuits in the past the sink signal of the master is generally 1.2 to 1.2 times faster.

    I think it might work, we cannot guarantee it.  I would suggest ordering one of the 600W EVMs and trying it to see what happens.  You can find a link to the users guide at the following link.

     

    Regards,