Application information

STBB2

18/25

DocID022745 Rev 9

8

Application information

8.1

Programming the output voltage

The STBB2 is available in two versions: fixed output voltage and adjustable output voltage.

In the first case the device integrates the resistor divider needed to set the correct output

different output voltages, programmed internally by the VSEL pin, can be selected. For the

to FB as shown in Figure 19.

Equation 1

Figure 19. Adjustable output voltage

A suggested value for R2 is 100 k

Ω. To reduce the power consumption a maximum value of

500 k

Ω can be used.

8.2

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 following two conditions in

which the converter works:

•

as buck at the maximum operative input voltage of the application

•

as a boost at the minimum operative input voltage of the application

Two critical inductance values are then obtained according to the following formulas:









−

×

=

1

V

V

2

R

1

R

FB

OUT

AM10443v1

L1

C4

R1

C1

R2

C2

C3

GND

GND

GND

GND

FB

E3

GND

C3

GND

D3

PGND

C2

MODE

C4

VSEL

D4

BP

B4

EN

A4

VINA

A3

VIN

A1

VOUT

E2

PGND

C1

VOUT

E1

GND

E4

SW2

D2

SW2

D1

SW1

B1

SW1

B2

VIN

A2

VINA1

B3

STBB2

GND GND

GND

GND