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LM7480-Q1: Abnormally long turn-on delay in TINA simulation

Ella KIM
Expert 4212 points
Part Number: LM7480-Q1

Hi PS Folks,

May I know how ~9ms of long delay to turn on DGATE since VIN (VS pin) goes above its UVLO level 2.6V?

When you look at the waveform, VS (UVLO/EN pin) is already high with 5V, which indicates the LM7480-Q1 is already enabled. 

Please refer to TINA attached.

slvmdd1.tsc

Thank you!

  • 0
    TI__Guru 57737 points

    Hi Ella,

    Thanks for reaching out to us.

    We are currently on Holiday but we will take this on priority and get back to you when we are back to office on 01/03.

  • 0 in reply to Praveen GD
    TI__Guru 57737 points

    Hi Ella,

    For the DGATE to be enabled, the following conditions have to be met as described in the datasheet below,

    The below two factors contribute to the delay in DGATE turn ON,

    1. Because of the higher values of R1, R2 and C2 the voltage build up on VS and VCAP-VS voltage is delayed. This delays the turn ON of HGATE.
    2. There will be voltage build up on A pin only after the HGATE is turned ON. Because of the dvdt circuit on HGATE, the slew rate of CS point/ VA / the VOUT is slow. 

    You will understand better when you probe the voltages on A, VS, CAP-VS in the simulation.