STBB1XX STMicroelectronics, STBB1XX Datasheet - Page 13

• Manufacturer Part Number: STBB1XX
• Description: 1 A, high efficiency single inductor dual mode buck-boost DC-DC converter
• Manufacturer: STMicroelectronics

Specifications of STBB1XX

• Typical Efficiency: > 94 %

STBB1XX
8
8.1
8.2
Application information
Programming the output voltage
The STBB1 is available in two versions: fixed output voltage (STBB1PURXX) and adjustable
output voltage (STBB1PUR).
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 15474 Rev 5
−
Δ
Δ
VOUT
VIN
I
I
L
L
MIN
)
)
Application information
Figure
OUT
3.
and GND
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