A5974AD datasheet(37/49 Pages) STMICROELECTRONICS

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A5974AD

Application information

Doc ID 018762 Rev 1

37/49

Figure 25.

Positive buck-boost regulator

8.7

Negative buck-boost regulator

In Figure 26, the schematic circuit for a standard buck-boost topology is shown. The output

voltage is:

Equation 38

where the ideal duty cycle D for the buck-boost converter is:

Equation 39

The considerations given in Section 8.7 for the real duty cycle are still valid here. Also

Equation 35 to 37 can be used to calculate the maximum output current. So, for example,

considering the conversion VIN = 12 V to VOUT = -5 V, ILOAD = 0.5 A:

Equation 40

Equation 41

An important point to take into account is that the ground pin of the device is connected to

the negative output voltage. Therefore, the device is subjected to a voltage equal to VIN-VO,

which must be lower than 36 V (the maximum operating input voltage).

AM09690v1

10V

A5974AD

4.7

6.8

470

ESR>35m

OUT

–

-------------

⋅

–

OUT

–

------------------------------

512

----------------

0.706

LOAD

–

---------------

0.5

10.706

–

------------------------

1.7A

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