LM27762: The inrush current of LM27762

takahiko yokota

Mastermind 7135 points

Part Number: LM27762

My customer simulated LM27762 the following conditions.

But the input inrush current is 2.3A.

I simulated this device adding the resister on VIN, but I couldn't reduce the inrush current.

Are there there the method to reduce this inrush current?

Positve：Vin=3.3V, Vout=＋2.5V
Negative：Vin=3.3V, Vout=‐2.5V

Best regards,

Yokota

over 7 years ago

0 Chris Glaser over 7 years ago

TI__Guru**** 150940 points

Hi Yokota-san,

Can you share a waveform of the inrush? Is this simulated with the model or measured on hardware?

0 takahiko yokota over 7 years ago in reply to Chris Glaser

Mastermind 7135 points

Hi Chris-san

Thank you for the reply.

I simulated LM27762 using Webench,

I attached the simulation result.

LM27762.pdf LM27762(start up).pdf

Best regards,

Yokota

0 Chris Glaser over 7 years ago in reply to takahiko yokota

TI__Guru**** 150940 points

Thanks for sharing Yokota-san. This looks fairly accurate. The outputs ramp very quickly to their programmed value, starting fast, which draws inrush current.

If the application cannot tolerate this inrush current, more input capacitance can be used to buffer the energy from the power source so that its voltage doesn't drop as much.

0 takahiko yokota over 7 years ago in reply to Chris Glaser

Mastermind 7135 points

Hi Chris-san

Thank you for the answer.

I changing Cin to 47uF and simulated LM27762.

But the inrush current didn't reduce.

Are there any other method to reduce inrush current?

LM27762(start up, Cin=47uF).pdf LM27762(start up, Cin=10uF).pdf

Best regards,

Yokota

0 Chris Glaser over 7 years ago in reply to takahiko yokota

TI__Guru**** 150940 points

Hi Yokota-san,

What is the impedance of the power source? This should be given some impedance. Otherwise, the ESR of the input cap has a higher impedance and all the current will come from the input source.

0 takahiko yokota over 7 years ago in reply to Chris Glaser

Mastermind 7135 points

Hi Chris-san

Thank you for the reply.

The impedance of the power source is 1mΩ.

Best regards,

Yokota

0 Chris Glaser over 7 years ago in reply to takahiko yokota

TI__Guru**** 150940 points

Yes, so change this 100mOhm (or something more realistic of your battery) and watch the waveform change.

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LM27762: The inrush current of LM27762