DocID022745 Rev 9

15/25

STBB2

General description

7

General description

The STBB2 is a high efficiency dual mode buck-boost switch mode converter. Thanks to the

4 internal switches, 2 P-channels and 2 N-channels, it is able to deliver a well-regulated

output voltage using a variable input voltage which can be higher than, equal to, or lower

than the desired output voltage. This solves most of the power supply problems that circuit

designers face when dealing with battery powered equipment.

The controller uses an average current mode technique in order to obtain good stability in all

possible conditions of input voltage, output voltage and output current. In addition, the peak

inductor current is monitored to avoid saturation of the coil.

The STBB2 can work in two different modes: PWM mode or power save mode. In the first

case, the device operates with a fixed oscillator frequency in all line/load conditions. This is

the suitable condition to obtain the maximum dynamic performance. In the second case the

device operates in burst mode allowing a drastic reduction of the power consumption.

Top-class line and load transients are achieved thanks to a feed-forward technique and due

to the innovative control method specifically designed to optimize the performance in the

buck-boost region where input voltage is very close to the output voltage.

The STBB2 is self-protected from short-circuit and overtemperature. Undervoltage lockout

and soft-start guarantee proper operation during startup.

Input voltage and ground connections are split into power and signal pins. This allows

reduction of internal disturbances when the 4 internal switches are working. The switch

7.1

Dual mode operation

The STBB2 works at fixed frequency pulse width modulation (PWM) or in power save mode

(PS) according to the different operating conditions. If the MODE pin is pulled high the

device works at fixed frequency pulse width modulation (PWM) even at light or no load. In

this condition, the STBB2 provides the best dynamic performance. If the MODE pin is logic

low, the STBB2 operation changes according to the average input current handled by the

device. At low average current the STBB2 is in PS mode allowing very low power

consumption and therefore obtaining very good efficiency event at light load. When the

average current increases, the device automatically switches to fixed switching frequency

mode in order to deliver the power needed by the load. In PS mode the STBB2 implements

a burst mode operation: if the output voltage increases above its nominal value the device

switching.

7.2

Enable pin

The device turns on when the EN pin is pulled high. If the EN pin is low the device goes to

shutdown mode and all internal blocks are turned off. In shutdown mode the load is

electrically disconnected from the input to avoid unwanted current leakage from the input to

the load and the current drawn from the battery is lower than 1 µA in the whole temperature

range.