DocID025425 Rev 5

15/27

STBB3JCC

General description

7

General description

The STBB3JCC 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 STBB3JCC 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 performance in the buck-

boost region where input voltage is very close to the output voltage. In HB WLED driver

configuration, the MODE pin must be set high in full PWM mode operation.

The STBB3JCC is self-protected from overcurrent 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 STBB3JCC 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 STBB3JCC provides the best dynamic

performance. If the MODE pin is pulled low, at low average current the STBB3JCC 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 STBB3JCC

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 29 shows PS mode operation areas vs. output current in typical application

conditions. If the device is used in HB LED driver configuration, the MODE pin must be

pulled high to assure the best dynamic performance at the start-up phase.