L6986I datasheet(55/60 Pages) STMICROELECTRONICS

55 / 60 page

Contents

Application schematic .............................................................2

Pin connection ....................................................................3

2.1

Maximum ratings ............................................................... 4

Electrical characteristics...........................................................5

Functional description .............................................................8

4.1

Primary side ................................................................... 8

4.1.1

Power supply and voltage reference .......................................... 9

4.1.2

Switchover feature ...................................................... 10

4.1.3

Voltage monitor ......................................................... 10

4.1.4

Error amplifier .......................................................... 10

4.2

Transformer .................................................................. 10

4.3

Secondary side ............................................................... 10

4.4

Iso-buck operation principle ..................................................... 11

4.5

Soft-start and inhibit ........................................................... 12

4.6

Minimum On-Time............................................................. 14

4.7

Output voltage line regulation ................................................... 16

4.8

Output voltage load regulation................................................... 18

4.9

Overcurrent protection ......................................................... 19

4.10

Overvoltage protection ......................................................... 21

4.11

Thermal shutdown............................................................. 22

Closing the loop ..................................................................23

5.1

GCO(s)control to output transfer function .......................................... 23

5.2

Error amplifier compensation network ............................................ 24

5.3

Voltage divider ................................................................ 25

5.4

Total loop gain ................................................................ 25

5.5

Compensation network design .................................................. 26

Application notes .................................................................28

6.1

Output voltage adjustment ...................................................... 28

6.2

Switching frequency ........................................................... 29

L6986I

Contents

DS13647 - Rev 1

page 55/60

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