L7987L datasheet(35/41 Pages) STMICROELECTRONICS

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L7987L

Application ideas

The current flowing through the internal power MOSFET is transferred to the load only

during the OFF time, so according to the maximum allowed L7987L DC switch current

(2.0 A), the maximum output current for the buck-boost topology can be calculated from

Equation 35.

Equation 35

where ISW is the average current in the embedded power MOSFET during the ON time.

In addition to these constraints, the thermal considerations summarized in Section 5.5 on

page 29 must also be evaluated.

Figure 24. Buck-boost PCB layout (top and bottom)

The transfer function of the power section for buck-boost topology is summarized below:

Equation 36

With below singularities and parameters:

Equation 37

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