R5975D datasheet(37/47 Pages) STMICROELECTRONICS

Part #	R5975D

Description	Up to 3 A step-down switching regulator for aerospace applications

PDF	47 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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R5975D

Application information

8.7

Negative buck-boost regulator

In Figure 23, the circuit schematic 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

Equation 39 to 41 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 44

Equation 45

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).

Figure 23. Negative buck-boost regulator

VOUT

VIN

–

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



– OUT

VIN VOUT

–

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

512

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

0.706

ISW

ILOAD

–

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

0.5

10.706

–

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

1.7A

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