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TPS53014 Inductor current value

Other Parts Discussed in Thread: TPS53014, PMP8670

Hi,

My customer has question about TPS53014.
Could you tell us about question?

[Question]
 My customer has question about Inductor current value on PMP8670.
 She calculate TPS53014's current limit value on PMP8670. It is below.

  R10=6.81k (Vtrip=0.05)
  Low Side FET Rds(on)=2.3mohm(typ), 3mohm(max) at Ta=25deg

  Valley current limit value = Vtrip / Low Side FET Rds(on)
                                               = 16.7A(typ), 21.7A(max) at Ta=25deg

 But Inductor(L1) current value is 20.5A. She think there is danger of saturation.
 Could you explain how to choice inductor current value?

Best Regards,
tateo

  • I have forwarded your question to the circuit designer. He is out of the office, so you may expect a delayed response.
  • as you can see at schematics R10 is set to 6k81; CS (Vcs =50mV) trips at 19A load;

    BUT: current sense across RdsON is dependant on temperature and FET tolerances;

    so this is NOT a precise current limitation, it’s just a overcurrent protection.

    So I selected an inductor with saturation current of more than 40 Amps,

    please see the attached data sheet.

    To explain SATURATION for the lady:

    Saturation means that magnetic field strength inside the magnetic material get’s too high,

    so magnetic flux lines are leaving the core material; but flux leaving the magnetic core means

    that the length of the “gap” increases – so the inductance drops (and magnetic radiation=EMI increases);

    7443330047.pdf

    see L over I curve below, this drop of L starts around 40Amps.