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Original question:

TIDA-01505: Reference design calculations

TIDA-01505: TIDA-01505: Startup Circuit

SR
Prodigy 140 points
Part Number: TIDA-01505

As suggested, the R58 connection was moved to VDD Node & Changed the total resistor value of R38+R40+R42+R43+R45+R46 to 15K to enable the Self start up to avoid connecting the +20V & -5V externally. However this didn't work. Could you please suggest if there are any additional changes required to facilitate the self startup? If there any reduction envisaged in the resistor network ( R37,....,R49 ) from 9MOhm to a lower value to increase the base current of Q9?

  • 0
    TI__Genius 13660 points

    Hello SR,

    Sorry for the delay response. And thank you for your interest in Texas Instruments' Reference Designs. 

    I will track down the design engineer and  ask him to respond to your questions.

    Regards,

    Teng

  • 0
    TI__Mastermind 18120 points

    Please try to increase C54 to 220uF and remove the two times of 470uF output capacitors. The purpose is to hold the voltage at VDD sustainable to power the level shifter. Please first disconnect the load to see the effect. Could you please provide the startup waveform at nodes: "VDD" and "-5V" to see how the ramp up looks like? Thanks.