STBB3JCC Datasheet, PDF (15/27 Pages) STMicroelectronics – 2 A, high efficiency single inductor buck-boost DC-DC converter and high brightness WLED driver

STBB3JCC
7
General description
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
bridge is connected between the V_IN and PGND pins while all logic blocks are connected
between V_INA and GND.
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
the device stops switching; as soon the V_OUT falls below the nominal value the device
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.
DocID025425 Rev 5
15/27