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PMP30763: Regarding External UVLO circuit U13

Part Number: PMP30763

Dear TI Team,

In the schematic External Undervoltage Protection Circuit is given using U13 and output is connected to VREF using Diode .

When the U13 output is LOW , then UVLO circuit will active .

As in the IC UCC28064 , there is Brown out protection is programmable at VINAC pin, still will need external circuit ?

 Thank you.

Regards,

Sachin Khante

  • Hello Sachin,

    In order to comply with DO160 avionics standards, we had to set the VINAC bias properly and avoid too much Ton compensation. For this reason, by adding a DC bias on this pin, the internal brown out is not anymore active. The comparator U13 detects an UVLO condition, and when it happens, it removes the DC bias from VINAC by pulling it down by means of D15. This way, all input VAC zero-crossing events will be back and the internal brown out detection active again.

    Does it answer your question? Please let me know. Best regards,

    Roberto

  • Hello Robert,

    Thank you for your response.

    As per the Calculation UVLO = LOW when the input Voltage goes below 41.56VRMS.

    In this situation D15 will conduct , but how the circuit will turn off PFC as there is R16 =44.2K ohm between Vref and Anode of  D15.

    As per my understanding D15 Anode should be connected to Direct Vref , so Vref = Low , then PFC will turn off.

    Please give me your expert opinion.

    Thank you.

    Kind Regards,

    Sachin Khante

  • Hello Sachin,

    The main purpose of U13 is not to switch off the converter, because the internal brown out detection is performed at the peak of VAC, sensed at VINAC pin, see figure 28, page 29 of the datasheet. The main purpose of U13 is to let VINAC "see" again the zero crossing (by disabling the extra BIAS through R16, R18 and D6). When this added BIAS is disabled (by pulling down D15) the VINAC voltage should again be similar to what is shown in figure 29, page 30 of the DS; that means, the converter will again be able to detect the "AC-Line dropout" and have the COMP pin voltage ready, as soon as mains recovers. More information are available in the paragraph "8.3.12 Line Dropout Detection".

    Best regards,

    Roberto