LM5181: 0.1mA

Kuramochi Tadahiko

Guru 28715 points

Part Number: LM5181

Hi,

What is the origin of the following "0.1mA"?

Best Regards,

Kuramochi

over 3 years ago

0 J Arrigo over 3 years ago

TI__Mastermind 28020 points

Hi Kuramochi,

The 0.1mA is selected as a low current for the feedback divider. This ensures the device is dissipating very little power in this resistor.

Regards, Jason

0 Kuramochi Tadahiko over 3 years ago in reply to J Arrigo

Guru 28715 points

Jason-san,

Thank you for your quick help.

Why does the just low current decide VOUT?

I suppose that 0.1mA is originated from the internal current source around the FB pin.

Best Regards,

Kuramochi

0 J Arrigo over 3 years ago in reply to Kuramochi Tadahiko

TI__Mastermind 28020 points

Hi,

By using a low current FB divider, the device does not dissipate much power.

Regards, Jason

0 Timothy Hegarty over 3 years ago in reply to Kuramochi Tadahiko

TI__Mastermind 49597 points

Kuramochi-san,

The flyback reflected voltage = (Vout + Vd)*Nps is controlled such that 100uA flows in the FB resistor when the SW voltage is high and the flyback diode is conducting. This is the primary-side regulation (PSR) technique that provides accurate output voltage control.

Regards,

Tim

0 Kuramochi Tadahiko over 3 years ago in reply to Timothy Hegarty

Guru 28715 points

Tim-san,

Thank you for your support.

If RRSET is not 12.1kΩ, is this "0.1mA" changed?

Is the current value VRSET=1.21V(typ)/RRSET?

Best Regards,

Kuramochi

0 Timothy Hegarty over 3 years ago in reply to Kuramochi Tadahiko

TI__Mastermind 49597 points

Kuramochi-san,

Yes, that's correct. A lower RSET resistance gives a higher FB current, thus increasing Vout.

12.1k is the recommended value.

Regards,

Tim

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LM5181: 0.1mA