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LM53603-Q1: Question about BIAS protection

NOBUO FUJIHARA
Expert 8255 points
Part Number: LM53603-Q1

Hi team,

My customer uses LM53603-Q1 with the configuration similar to Figure 15 of the datasheet with Rbias=4.7 ohm setting.

 Q.1) It is required to pass the short-to-GND test for BIAS pin at customer side, the customer would like to remove Rbias between to avoid Rbias being broken due to high short-circuit current. 

Is it feasible to remove Rbias and put Schottky diode in parallel with Cbias instead?

 Q.2) When BIAS port was shorted to GND, device operate with stable Vout. Is it due to BIAS port and VIN are both supplied complementary to the internal voltage regulator?

Best regards,

  • 0
    TI__Expert 6165 points
    Hello Nobuo,

    The BIAS resistor is needed to protect in cases where output voltage falls below ground. This can happen if a short circuit through a wire with inductance is applied. Using a diode or grounding BIAS both work when preventing BIAS from dropping below ground. Using a diode will affect efficiency of the converter only if output voltage is below 4 V. If output voltage is 5 V, a diode will work well. If output voltage is 3.3 V, the diode’s effect on BIAS will be similar to grounding the BIAS pin – all VCC power (typically 30 mA at full frequency and 47 uA when the part is unloaded in Auto mode) will come from VIN rather than BIAS.

    Regards, Robert