2.7V-60V in, 250 mA linear battery charger for multi-chemistry cells

October 14, 2014 // By Graham Prophet
LTC4079, a 60V, constant-current/constant-voltage 250 mA multi-chemistry battery charger. The device’s low quiescent current linear topology offers a simple inductorless design and accepts a 2.7V to 60V input voltage range.

A resistor-programmable 1.2V to 60V battery charge voltage range with ±0.5% charge voltage accuracy and onboard charge termination makes the LTC4079 suitable for many battery chemistries, including Li-Ion, nickel and lead acid. The charge current is adjustable from 10 mA to 250 mA with an external resistor, and unlike competing chargers, the device maintains high accuracy at low charge currents. Typical applications include embedded automotive and industrial systems, backup battery charging, energy harvesting and thin film battery products.

The LTC4079's input voltage regulation function can regulate the IN pin to a constant voltage or to a constant differential voltage above the battery, when charging from a current-limited power source such as a weak battery or solar panel. These features can be used to prevent the input voltage from collapsing below the undervoltage lockout (UVLO) voltage, or to maintain the input source voltage at its peak power transfer point. The charge current is reduced as the input voltage falls below the programmed threshold. This regulation mechanism allows the charge current to be selected based on the battery requirement and the maximum available power from the charging input source, while letting the LTC4079 take care of situations when the input source cannot provide the full programmed charge current.

The LTC4079’s thermal regulation feature ensures maximum charge current up to the specified limit without the risk of overheating. Charging can be terminated via C/10 or an onboard adjustable timer. Other features include NTC thermistor temperature-qualified charging, bad battery detection, automatic recharge with sampled feedback in standby for negligible battery drain and an open-drain CHRG pin status output. Quiescent current while charging: Iin is 4µA, and battery drain in shutdown and charged state is under 0.01µA.

The LTC4079 is housed in a low profile (0.75 mm) 10-pin 3 x 3 mm DFN package with backside metal pad for thermal performance. The device is guaranteed for operation from -40°C to 125°C, in both E-and I-grades.