AN4501 datasheet(38/48 Pages) STMICROELECTRONICS

Part #	AN4501

Description	Design of a boost LED driver using L99LD01

PDF	48 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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38 / 48 page

Selection of the switching MOSFET

AN4501

38/48

DocID026394 Rev 1

Initial estimation of TJ (noted TJ1). For example, we can use TAMB as a starting point.

Calculation of the corresponding Rdson, using the Rdson at 25°C and the thermal

coefficient

Calculation of the conduction losses in M1

Calculation of the total power losses in M1

Calculation of the resulting junction temperature (noted TJ2)

Calculation of the RDSON corresponding to TJ2

The calculation is finished if the difference between RDSON at TJ1 and TJ2 is smaller

than the required precision. The final RDSON and junction temperature are respectively

RONM1@TJ2 and TJ2.

If the difference between Rdson at TJ1 and TJ2 is higher than the required precision we

substitute TJ1 by TJ2 and we restart a new iteration.

Figure 18. Flowchart for the iterative calculation of the junction temperature of M1

AN4501 Datasheet(PDF) 38 Page - STMicroelectronics