Hot!Help using Micrel MIC2101

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andrefleitao
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2018/03/07 17:23:21 (permalink)
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Help using Micrel MIC2101

Hi.
 
I noticed that the Pololu D24V50F5 Step-Down voltage regulator uses the Micrel MIC2101 controller. Their
inductor is 1.8 uH (1R8 in the image here https://a.pololu-files.co...6a58c48aa66a6b29cf674) but in the Micrel datasheet says that for a Vout of 5 V, a Iout max o 5 A and a Vin max of 38 V and a switching frequency between 200 and 600 kHz the inductor should be between 9 and 22 uH. How is this possible? Am i missing something? For 1.8 uH only if Vin is at the minimum of 6V but the equation states Vin max (not Vin min). Can someone help me solve this mistery?
 
Best regards,
André
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    Bob White
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    Re: Help using Micrel MIC2101 2018/03/08 20:30:05 (permalink)
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    A quick calculation says that in the worst case the expected peak-to-peak ripple current is about 4 A (80% of the rated output).  That will work but results in higher losses in the inductor and in the MOSFETs.  One can only conclude that Pololu (or whoever actually designed this board) concluded that the smaller physical size of the inductor is worth the extra losses.
     
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