STBB1-APUR Datasheet, PDF (10/22 Pages) STMicroelectronics – 1 A, high efficiency single inductor dual mode buck-boost DC-DC converter

Detailed description
6
Detailed description
STBB1-AXX
6.1
General description
The STBB1-A is a high efficiency dual mode buck-boost switch mode converter. Thanks to
the 4 internal switches, 2 P-channel and 2 N-channel, and its unique control mechanisms it
is able to deliver e 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 STBB1-A 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-A is self protected from short circuit and over-temperature.
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 VIN and PGND pins while all logic blocks are connected
between VINA and GND.
6.2
Dual mode operation
The STBB1-A 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 only in PWM mode even at light or no load.
In this condition STBB1-A provides the best dynamic performance.
If the MODE pin is logic low, the STBB1-A operation changes according to the average input
current handled by the device.
At low average current the STBB1-A 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-A 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.
10/22
Doc ID 022197 Rev 2