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TPS23750 application question

Dear Sir

Good days,

My customer(Vout 12V/1A) use PMP1360 reference design in their project and may we check some question with you?

*. we connect  BL pin in "REF" pin. but PMP1360 BL pin is connect to ground. is this will case any issue?

  I am not clear datasheet page9 explain.

*.Due to cost down, we have change Optocoupler from TCMT1107 to PC817A(CTR 80 to 160). Is also ok?

                                                                    Best regards,

                                                                                       Bogey

 

 

3 Replies

  • Blanking suppresses current sense operation at the beginning of the primary MOSFET switch ON period.  When the MOSFET is turned on, there is a Source current that is due to the charge of the gate-source capacitance, currents resulting from drain voltage swing, and currents that might be due to output rectifier turn-off recovery (or other active devices in the circuit).  Often this is referred to as a turn-on current spike.  Oftentimes this spike magnitude can be larger than the programmed peak current limit or controled peak current (as in current-mode control), causing a false turnoff of the MOSFET.  

    Blanking is then one simple way of avoiding this problem.   The downside to this is that the MOSFET current is uncontrolled (no protection) during this interval.  Choice of the blanking interval is a tradeoff between clean operation (no false current limit switching) and device failure under shorted conditions of the output, or various devices around the MOSFET. 

    In your case, you have made the period longer.  Be convinced that susceptability to failures is within your tolerance.  Direct measurement of the "spike" is recommended.  Bear in mind that false triggers are often their worst at light load in current-mode control.

    PC817A (Sharp) looks like a suitable substitution.  As always, you should test the change to validate it through phase-gain or (second choice) transient response.

  • In reply to Martin Patoka:

    Dear Sir

    Many thanks for you reply,

    we met some issue that we test our board(reference PMP1360 Vout :12V/1A). when we power source to use adapter in. then output voltage start up is normal.

    But when we power source use PSE, then output start up sometime normal. but sometimes output will steady 4.5V a few seconds then reach to normal 12V.

    May you pls have some suggestion to us for debug?

                                                                    Best regards,

                                                                                  Bogey

     

  • In reply to Chen Bogey:

    The PoE input source is current limited.  See the datasheet section "Converter Startup."