Out in Front: June 6, 1996
An integrated PWM battery charger provides nearly all the circuitry you need to fast-charge lithium-ion, nickel-metal-hydride, NiCd, and lead-acid batteries during full system operation. The LT1511 from Linear Technology Corp constant-current/constant-voltage charger delivers as much as 3A charging current, programmed with 5% accuracy via a resistor or DAC; in voltage-charge mode, charging accuracy is 0.5%. An internal control loop regulates the current drawn from the charging source, such as an ac wall adapter, thus keeping sourcing current lower than specified levels and preventing overload when you are charging the battery and supplying the load.
The IC operates and supports charging from a dc source ranging from 8 to 28V, which is compatible with most wall adapters and automotive battery inputs. It can charge batteries from 1 to 20V, as long as the supply source is 3V greater than the battery being charged. Overall efficiency is 90%. Current sensing can occur at either battery terminal: The LT1511 does not require ground sensing of current, so you can connect the negative battery terminal to ground. The device requires no external battery-blocking diode, because the IC goes into an automatic-shutdown sleep mode and draws just 3 µA when you unplug the charging source. The data sheet for the device provides detailed application information and discusses board layout for critical electrical and thermal paths. The 24-lead SOIC device costs $5 (1000).
—by Bill Schweber
Linear Technology Corp, Milpitas, CA. (800) 454-6327, fax (408) 434-6441.