STBB1-APUR STMicroelectronics, STBB1-APUR Datasheet - Page 14

• Manufacturer Part Number: STBB1-APUR
• Description: 1 A, High Efficiency Single Inductor Dual Mode Buck-boost Dc-dc Converter
• Manufacturer: STMicroelectronics

Application information
8
8.1
8.2
14/22
Application information
Programming the output voltage
The STBB1-A is available in two versions: fixed output voltage (STBB1-APURXX) and
adjustable output voltage (STBB1-APUR).
In the first case the device integrates the resistor divider needed to set the correct output
voltage. This allows the saving of 2 external components. The FB pin must be connected
directly to V
For the adjustable version, the resistor divider must be connected between V
and the middle point of the divider must be connected to FB as shown in
Equation 1
A suggested value for R2 is 100 kΩ. To reduce the power consumption a maximum value of
500 kΩ can be used.
Inductor selection
The inductor is the key passive component for switching converters. With a buck-boost
device, the inductor selection must take into consideration the boundary conditions in which
the converter works, as buck at the maximum input voltage and as a boost at the minimum
input voltage.
Two critical inductance values are then obtained according to the following formulas:
Equation 2
Equation 3
where:
fs: minimum switching frequency
ΔI
can be set at 10% - 20% of the output current.
L
L
R
MIN
MIN
1
L
=
= the peak-to-peak inductor ripple current. As a rule of thumb, the peak-to-peak ripple
−
−
R
BOOST
BUCK
2
×
⎛
⎜ ⎜
⎝
=
V
OUT
V
=
OUT
VOUT
FB
VIN
.
−
VIN
MIN
1
VOUT
⎞
⎟ ⎟
⎠
×
(
MAX
×
VIN
(
VOUT
×
MAX
×
fs
fs
×
×
Doc ID 022197 Rev 2
−
−
Δ
Δ
VOUT
VIN
I
I
L
L
MIN
)
)
Figure
OUT
STBB1-AXX
3.
and GND