BQ24105-Q1: Recommended inductor values

Dear Koji,

The inductor value can be calculated from those parameters and is determined by the desired settings of the user. The value comes out to 55.9 uH. Please make sure the output capacitor is properly set by Equation 9.

Thanks,

Mike Emanuel

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Hi Mike-san

Thank you for response.

I think 55.9uH is a large value.

Let me return to the first question.

http://www.ti.com/jp/lit/an/slua843/slua843.pdf

Figure 3. shows the value of Lout is 10μH.

How was the 10 μH calculated ?

Best Regards,

Koji Hayashi

Koji-san,

The inductor is selected based upon the datasheet recommendation.

Thanks,

Mike Emanuel

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Hi Mike-san

Thnak you for respose.

If I use the formula, it will be several hundred μH.

How do you calculate the recommended value ?

Best Regards,

Koji Hayashi

Koji-san,

On page 21 of the datasheet, there is a detailed calculation for the selection of the inductor. You start with the battery voltage, max input voltage, and ripple current values. Then, a standard inductor is chosen and the ripple is calculated again to see if it is acceptable. Last, the inductor is finally selected for a saturation current to satisfy the peak current in the inductor based upon the previous calculations.

Please note in the first calculation that if you have a smaller charge current, and an even smaller ripple, the denominator of the Lout equation is small, making the value of the inductor larger. To have a smaller ripple, a larger inductance value is needed.

Thanks,

Mike Emanuel

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Hi Mike-san

Thank you for response.

I will use this formula to do the math.

Please tell me Icharge and BB of application note.

Best Regards,

Koji Hayashi

Koji-san,

The fast charge current is 50 mA. It is calculated using Equation 2 of the application note.

What do you mean by the BB?

Thanks,

Mike Emanuel

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Hi Mike-san

Thank you for response.

Sorry, I made a mistake.

Please tell me VINMAX of application note.

If VINMAX=16V, L=211uH.

(VBAT=5.1V,freq=1.1MHz, Icharge=0.05A) 

Best Regards,

Koji Hayashi

Koji-san,

The recommended supply voltage as outlined in page 2 of the datasheet under "Recommended Operating Conditions" is 16 V. Please make sure this voltage does not go above the absolute maximum rating of 20 V as denoted under the operating condition.

Thanks,

Mike Emanuel

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