a5975d STMicroelectronics, a5975d Datasheet - Page 37

• Manufacturer Part Number: a5975d
• Description: Up To 3 A Step-down Switching Regulator For Automotive Applications
• Manufacturer: STMicroelectronics

A5975D
8.7
Figure 25. PCB layout (front side)
Positive buck-boost regulator
The device can be used to implement a step-up/down converter with a positive output
voltage.
The output voltage is given by:
Equation 33
where the ideal duty cycle D for the buck-boost converter is:
Equation 34
However, due to power losses in the passive elements, the real duty cycle is always higher
than this. The real value (that can be measured in the application) should be used in the
following formulas.
The peak current flowing in the embedded switch is:
Equation 35
while its average current is equal to:
Equation 36
This is due to the fact that the current flowing through the internal power switch is delivered
to the output only during the OFF phase.
I
SW
=
Doc ID 018760 Rev 1
I
-------------- -
1 D
LOAD
–
V
+
D
OUT
I
------------------- -
I
RIPPLE
SW
=
2
----------------------------- -
V
=
=
IN
V
V
I
-------------- -
IN
+
1 D
LOAD
OUT
=
V
–
⋅
OUT
I
-------------- -
------------ -
1 D
1 D
LOAD
D
–
–
+
---------- -
2 L
V
⋅
IN
⋅
---------
f
SW
D
Application information
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