STBB1XX Datasheet, PDF (9/20 Pages) STMicroelectronics – Buck-boost DC-DC converter

STBB1xx
6
Detailed description
Detailed description
6.1
General description
The STBB1 is a high efficiency dual mode buck-boost switch mode converter. Thanks to the
internal 4 switches, 2 P-channel and 2 N-channel, and its particular control technique it is
able to deliver e well regulated output voltage with a variable input voltage which can be
higher, equal 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 in order to avoid saturation of the coil.
The STBB1 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 performances. In the second case the
device operates in burst mode allowing a drastic reduction of power consumption.
Top-class line and load transients are achieved thanks to 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 STBB1 is self protected by short circuit, over-temperature and adjustable version.
Under voltage lockout and soft start guarantee proper operation during start-up.
Input voltage and ground connections are split in power and signal pins. This allows
reducing internal disturbances when the 4 internal switches are working. The switches
bridge is connected between VIN and PGND pins while all logic blocks are connected
between VINA and GND.
6.2
Dual mode operation
The STBB1 works in PWM or in power save (PS) mode according to the different operating
conditions.
If the Mode pin is pulled high the device works always in PWM mode even at light or no load.
In this condition STBB1 provides the best dynamic performances.
If MODE pin is logic low, the STBB1 operation changes according to the average input
current handled by the device.
At low average current the STBB1 enters in PS mode allowing very low power consumption
and thus 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 STBB1 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 starts switching again with a programmed average current higher
than the one needed by the load. Figure 8 in Section 7 shows PS mode operation areas vs
output current in typical application conditions.
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