STBB3J Datasheet, PDF (17/25 Pages) STMicroelectronics – 2 A, high efficiency single inductor buck-boost DC-DC converter

STBB3J
Application information
7.4.3
Overtemperature protection
An internal temperature sensor continuously monitors the IC junction temperature. If the IC
temperature exceeds 160 °C (typ.), the device stops operating. As soon as the temperature
falls below 140 °C (typ.), normal operation is restored.
8
8.1
8.2
Application information
Programming the output voltage
The external resistor divider must be connected between V_OUT and GND and the middle
point of the divider must be connected to FB.
The value for the resistor R2, placed between FB and GND, should be chosen in order to
set the divider current at 1 µA. The recommended value for this resistor is in the range of
500 kΩ but to reduce the power consumption a maximum value of 200 kΩ can be used.
The value of the resistor R1, connected between V_OUT and FB, is function of the output
voltage and can be calculated using the equation 1:
Equation 1
R1
=
R2
×


-^V--_V--^O--_F--^U-_B--^T--
–
1_
Figure 26. Application schematic
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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 region at the maximum input voltage
• as boost region at the minimum input voltage
Two critical inductance values are then obtained according to the following formulas:
DocID025263 Rev 5
17/25