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LM5156: PGOOD pin

d_zero
Genius 4775 points
Part Number: LM5156

Hi All,

i have one question regarding the pgood pin of LM5156.
I'm using UVLO resistors on pin 14 on our LM5156 to set under voltage lock-out.
Our Vin = 24V, and UVLO is se to 20V, when the UVLO happens ( the input voltage falls below 20V) the LM5156 will have the same voltage on its output as on input ( eg if input is 18V the output will be also 18V)
But the PGOOD pin is still low, is it correct that the PGOOD doesn't indicate UVLO error ?
( if i'm reading DS correctly the PGOOD should be pulled high when an error happens)
Best Regards,
David.
  • +1
    TI__Genius 11215 points

    Hello, 

    Thanks for reaching out. In this case this is not a UVLO/PGOOD error: the controller is off (meaning that it is not boosting the Vout), but in an asynchronous boost there is a direct connection between the Vin and the Vout through the diode, therefore you will see the same Vin voltage at the output. The output voltage is following the Vin also in case Vin>Vout. Please let me know if you need further help or I misunderstood the question.

    Kind regards, 
    EM