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UCC28180: Inquiry on Low Voltage Operation of UCC28180

Conor
Guru 11000 points
Part Number: UCC28180

Tool/software:

Hi,

We are currently considering a circuit that boosts from a rectified voltage of approximately 30V to around 170V. Since the UCC28180 does not directly detect the input voltage, we believe it could operate properly with appropriate resistor adjustments. Is this assumption correct?

The Vsense pin will halt operation when it drops below 0.82V. This function can be adjusted through the resistor divider, and we believe that the boost from 30V to 170V should work without issue. Is this understanding correct?

■Additional Information
When attempting to set up the design using TI's WEBENCH tool, we found that input voltages below AC 46V cannot be selected. This raised a question about whether there is a minimum guaranteed operating voltage.

■Example Settings
In our resistor configuration, we have attempted two setups to achieve a target boost voltage:

Thanks,

Conor

  • 0
    TI__Mastermind 36940 points

    Hello Conor-san, 

    Thank you for your questions on UCC28180 operation. 

    I believe that your assumptions are correct.  The UCC28180 should be able to boost a 30-V input to about 170V output.  The VSENSE resistor divider can be adjusted to ensure that the 0.82V start-up threshold is met with a 30V input.  These assumptions are valid based on nominal parameters.

    To ensure operation under worst-case conditions, more details must be considered. 
    1.  Is input voltage specified as peak value or RMS value.  The yellow highlight in the spreadsheet implies that 30V is a peak value. 
    2.  Minimum tolerance of input voltage.  For example, 30V +/- 10% => 27Vpk minimum at input.
    3.  Voltage drops between input source and output VSENSE divider (such as diode drops) may reduce the peak even further.  Fortunately at start-up, there is no load current after peak-charging the PFC output capacitor, so diode drops should be nearly ~0V. 
    4.  Tolerance on VSENSE divider resistors (typically +/-1%).
    5.  Tolerance on OLP threshold.  0.82V is a nominal value based on typical 16.5% of Vref, however this threshold has a min/max range relative to Vref and Vref has its own tolerance over temperature: 
      
     

    So, if VREF is maximum and Volp is maximum and the divider ratio is minimum under some hypothetical worst-case condition, the PFC may not be able to start up at the absolute minimum input voltage for target Vout = 174.5V.   You may have to reduce the target Vout somewhere below 174.5V to ensure reliable start-up. 
    The final answer depends on comprehensive inclusion of the details. 

    Regards,
    Ulrich