For charging relatively low capacity batteries, or maintenance charging backup and keep-alive batteries, linear topology battery chargers are valued for their compact footprints, simplicity and affordability. Even so, there is a dearth of linear chargers that accept a 10V or higher input voltage, leaving many industrial and automotive systems underserved.
Some switch mode solutions can accept high input voltages and switching topologies offer current and efficiency advantages, but they also incur significant costs in complexity and solution footprint. In the end, a switch mode solution is usually overkill for the low currents necessary in keep-alive systems or backup battery chargers. Furthermore, few are suitable for automotive and industrial applications up to 60V.
TheLTC4079is a wide input range standalone charger that can be powered by any DC source from 2.7V up to 60V, enabling CC/CV charging directly from 12V and 24V DC system rails, or even 48V industrial supplies. Its marriage of simplicity and robustness allow it to easily satisfy the charging needs of keep-alive systems or backup battery solutions in these environments. Figure 1 is an example of a simple Li-Ion battery charger.
Fortitude and Flexibility, Neatly Packaged
TheLTC4079’s charge voltage is resistor-programmable, matching the flexibility of its wide input voltage range for practical purposes. The circuit is stable across the entire input voltage range with minimal input and output capacitance.
Using a single resistor on the PROG pin, charge current is programmable up to 250mA and can be monitored in proportion to the PROG voltage. Charge termination functionality is familiar: timer-based, programmed via TIMER pin capacitance, or, C/10 current detection by connecting the TIMER pin to ground. /CHRG status signals termination by either method. The timer capacitor is also used for bad-battery detection.
Temperature-qualified charging can be implemented via the NTC and NTCBIAS sensing network to round out the full charger circuit. TheLTC4079’s thermally enhanced 3mm × 3mm DFN package includes an internal pass element, producing a compact and comprehensive solution. The complete circuit featured in Figure 2 shows its compact footprint.