This reference design shows the use of a buck-boost capability of a single-ended primary-inductor converter (SEPIC). Since the input and output are separated by a capacitor, this topology can be used to charge a battery with variable VIN as well as variable VOUT. A synchronous peak-current mode controller LM5122 is used; this IC can drive the high-side sync-FET by means of level shift (RCD network). By applying 9V to 36V input, this board can be used to charge two batteries in series with a voltage range of 8V to 28V, up to 2A charging current, or used as standard constant-voltage power supply. Both setpoints of output voltage and current are defined by two trimmers, even though both references can also be replaced by using two digital-to-analog converters.
Features
- Can be used as battery charger or standard power supply
- Synchronous SEPIC topology with external highside field-effect transistors (FETs) and low-side FETs
- Constant charging current: adjustable from 0A to 2A
- Constant supply voltage : adjustable from 8V to 28V
- ±2% charging voltage accuracy and ±2.5% charging current accuracy
- Selectable forced PWM mode or diode emulation mode for efficiency improvement at light load