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LMR36015: Operating in Dropout

Part Number: LMR36015

I am using the LMR36015B (1MHz) device. The output voltage is set to 5V. The input voltage varies, and sometimes may drop below 5.5V all the way down to 4.75V.

In such cases I am relying on the device operating in Dropout mode, where the switching frequency goes down, Toff is minimized, and you get as an output voltage the input voltage minus conduction losses minus PWM duty cycle losses as explained in sections 9.4.3 and 9.4.4 in the datasheet.

Unfortunately I need to use the LMR36015B, the 1MHz version, since this is a cost critical application and the inductor cost and size for the 400KHz solution are not acceptable.

The datasheet contains minimum switching frequency values and typical dropout charts for the 400KHz device only. How do I calculate the voltage drop for the 1MHz device?

  • Hi Yishai-san,

    As described on data sheet, the maximum T-on is 7us typical, so the switching frequency will drop to its minimum value of about 140 kHz, this is same behavior for all freq versions. 

    As your output is 5V, so you can refer to the Figure of Overall Dropout Characteristic VOUT = 5 V on data sheet.

    B R

    Andy