Photoflash Capacitor Chargers with Output Voltage Monitor and Integrated IGBT Drive

The LT3485 family of photoflash chargers are highly integrated ICs containing complete charger and IGBT drive functions. The patented control technique of the LT3485-x allows it to use extremely small transformers. Output voltage detection requires no external circuitry. The turns ratio of the transformer controls the final charge voltage. While charging, the output voltage on the capacitor may be monitored by a microcontroller from the monitor pin. Each device contains an on-chip high voltage NPN power switch, which can withstand negative voltages on the switch pin without an external Schottky diode. The device features a VBAT pin, which allows the use of two AA cells to charge the capacitor. The internal circuitry operates from the VIN pin. The LT3485-0 has a primary current limit of 1.4A, whereas the LT3485-3, LT3485-2, and LT3485-1 have current limits of 2A, 1A and 0.7A respectively. These different current limits result in tightly controlled input currents.

The CHARGE pin gives full control of the part to the user. Driving CHARGE low puts the part in shutdown. The DONE pin indicates when the part has completed charging. The LT3485 series of parts are housed in a leadless (3mm × 3mm) DFN package.

Applications

* Digital Camera and Cell Phone Flash Charger

* Integrated IGBT Driver

* Voltage Output Monitor

* Uses Small Transformers: 5.8mm × 5.8mm × 3mm

* Operates from Two AA Batteries, Single Cell Li-Ion

or Any Supply from 1.8V up to 10V

* No Output Voltage Divider Needed

* No External Schottky Diode Required

* Charges Any Size Photoflash Capacitor

* Available in 10-Lead (3mm × 3mm) DFN