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LM5146-Q1: how does pre biased startup work

Mahendra Patel1
Expert 3560 points
Part Number: LM5146-Q1
Other Parts Discussed in Thread: LM5146

Hello Team,

My customer is doing design analysis of LM5146-Q1 based design.

They want to understand mechanism for pre-biased startup, as they always have a battery connected at the output.

This explanation will help them to understand, if there are any possibility of system failure during startup.

Regards,

Mahendra

  • 0
    TI__Mastermind 27045 points

    Hi Mahendra,

    During startup process, if the output is biased to certain voltage >0V, the FB voltage will be higher than the reference voltage for soft startup, then the control logic will drive low-side FET turn-on till it trips the negative current limit, circuit works more like a boost converter to transfer energy from output to input. this operation will sink big current from output and may cause output dip or the pass through device for bias to be damaged.

    LM5146 works at Diode Emulation Mode during startup, which means the low-side FET works as a Diode to block the negative current from SW (low side FET drain) to GND (low side FET source), the circuit starts normal switching till the reference voltage for soft start ramp up to FB voltage.

    B R

    Andy