SEPIC Constant-Current/Constant-Voltage Battery Charger

The LT1512 is a 500kHz current mode switching regulator specially configured to create a constant-current/constant-voltage battery charger. In addition to the usual voltage feedback node, it has a current sense feedback circuit for accurately controlling output current of a flyback or SEPIC (Single-Ended Primary Inductance Converter) topology charger. These topologies allow the current sense circuit to be ground referred and completely separated from the battery itself, simplifying battery switching and system grounding problems. In addition, these topologies allow charging even when the input voltage is lower than the battery voltage.

Maximum switch current on the LT1512 is 1.5A. This allows battery charging currents up to 1A for a single lithium-ion cell. Accuracy of 1% in constant-voltage mode is perfect for lithium battery applications. Charging current can be easily programmed for all battery types.

Applications

* Battery Charging of NiCd, NiMH, Lead-Acid or Lithium Rechargeable Cells

* Precision Current Limited Power Supply

* Constant-Voltage/Constant-Current Supply

* Transducer Excitation

*Maximum Input Voltage = 40V – VBAT

* Charger Input Voltage May Be Higher, Equal to or Lower Than Battery Voltage

* Charges Any Number of Cells Up to 30V*

* 1% Voltage Accuracy for Rechargeable Lithium Batteries

* 500kHz Switching Frequency Minimizes Inductor Size

* 100mV Current Sense Voltage for High Efficiency

* Battery Can Be Directly Grounded

* Charging Current Easily Programmable or Shut Down