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TPS2493: Current limit / power limit operation / retry timing

K.Shidara
Expert 3225 points
Part Number: TPS2493

Hi Team,

Would you advise below three questions from the customer?

1. From data sheet P23, is the ton calculated in equation (14) the time to charge

　the output capacitor Co to Vcc (max),and is it correct to understand that the time to charge the

　TIMER capacitor Ct from 1V to 4V at the same time?

２．Is the time to charge the TIMER capacitor Ct from 1V to 4V from the current limit / power limit detection to the start of

　operation (FET turn OFF)?

３．After the limit operation starts, the sequence is to retry when 16 cycles of charge / discharge

　to Ct are repeated (P19 Figure 18). The period of 16 cycles is the ratio of ton and charge / discharge

　time (1:10 ) Or is Tretry calculated by the formula (26) on page 26 applicable to a period of 16 cycles?

Thanks 

Best regards,

Shidara

  • 0
    TI__Guru** 105361 points

    Hi Shidara,

    Thanks for reaching out!

    I will get back to you by early next week.

    BR, Rakesh

  • 0 in reply to Rakesh
    TI__Guru** 105361 points

    Hi Shidara,

    1A) Equation (14) determines the time the system takes to charge the output capacitance under power limit startup. The TIMER capacitor Ct value should be selected higher so that the circuit does not time out and successfully starts up.

    2A) During current limit/power limit detection, the TIMER capacitor Ct charges from  0V to 4V where as in retry mode it is between 1V to 4V  and then to 1V as shown in Figure 18.

    3A) Equation (25) considers both charge and discharge cycles.

    Retry time = 1 cycle to charge from 0V to 4V @ 27uA  +  15 cycles to charge from 1V to 4V @ 27uA   +  16 cycles to discharge from 4V to 1V @ 2.5uA

                      =  CT * 4/27uA  +  15* CT * 3/27uA  +  16* CT * 3/2.5uA    

    Solving above gives Equation (25).

    BR, Rakesh