A5974D datasheet(36/46 Pages) STMICROELECTRONICS

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A5974D

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DocID018774 Rev 2

Figure 26 shows the schematic circuit of this topology for a 12 V output voltage and

5 V input.

Figure 26. Positive buck-boost regulator

8.8

Negative buck-boost regulator

In Figure 27, the schematic circuit for a standard buck-boost topology is shown. The output

voltage is:

Equation 42

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

Equation 43

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

Also the Equation 39 till Equation 41 can be used to calculate the maximum output current.

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

Equation 44

Equation 45

An important thing 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).

VOUT

VIN

–

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



– OUT

VIN VOUT

–

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

512

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

0.706

ISW

ILOAD

–

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

0.5

10.706

–

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

1.7A

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