Datasheet

A5972D Application information
Doc ID 13956 Rev 5 29/37
Figure 20. Positive buck-boost regulator
8.7 Negative buck-boost regulator
In Figure 21, the schematic circuit for a standard buck-boost topology is shown. The output
voltage is:
Equation 37
where the ideal duty cycle D for the buck boost converter is:
Equation 38
The considerations given in Section 8.7 for the real duty cycle are still valid here.
Also the Equation 34 till Equation 36 can be used to calculate the maximum output current.
So, as an example, considering the conversion V
IN
= 12 V to V
OUT
= -5 V, I
LOAD
= 0.2 A:
Equation 39
Equation 40
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 V
IN
-V
O
,
which must be lower than 36 V (the maximum operating input voltage).
V
OUT
V
IN
D
1D
-------------
=
D
V
OUT
V
IN
V
OUT
----------------------------- -=
D
5
512+
---------------- 0.706==
I
SW
I
LOAD
1D
---------------
0.2
10.706
------------------------ 0.7A== =