DocID025263 Rev 5

15/25

STBB3J

General description

7

General description

The STBB3J 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 a peak 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 STBB3J can work in two different modes: PWM mode or power save mode. 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 performances in the buck-

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

The STBB3J 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 STBB3J works in PWM mode or in power save mode (PS) according to the different

status of the MODE pin. If the MODE pin is pulled high the device works in PWM only. In this

case the device operates at 2 MHz fixed frequency pulse width modulation (PWM mode) in

all line/load conditions. In this condition, the STBB3J provides the best dynamic

performance. If the MODE pin is pulled low, at low average current the STBB3J enters 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 PWM mode in order to deliver the power needed by the load. In PS mode the STBB3J

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

restarts switching with a programmed average current higher than the one needed by the

load. Figure 25 shows PS mode operation areas vs. output current in typical application

conditions.