Photoflash Capacitor Chargers with Automatic Refresh

The LT3420/LT3420-1 charge high voltage photoflash capacitors quickly and efficiently. Designed for use in both digital and film cameras, these devices use a flyback topology to achieve efficiencies up to four times better than competing flash modules. A unique adaptive off-time control algorithm* maintains current-limited continuous mode transformer operation throughout the entire charge cycle, eliminating the high inrush current often found in modules.

The LT3420/LT3420-1 output voltage sensing scheme* monitors the flyback voltage to indirectly regulate the output voltage, eliminating an output resistor divider or discrete zener diode. This feature allows the capacitor to be held at a fully charged state without excessive power consumption. Automatic refresh (which can be defeated) allows the capacitor to remain charged while consuming an average input current of about 2mA, at a user-defined refresh rate. A logic high on the CHARGE pin initiates charging, while the DONE pin signals that the capacitor is fully charged.

The LT3420/LT3420-1 are available in 10-Lead MSOP and (3mm × 3mm) DFN packages.

*Protected by U.S. Patents including 6518733.

Applications

* Digital Camera Flash Unit

* Film Camera Flash Unit

* High Voltage Power Supplies

* Charges 220µF to 320V in 3.7 Seconds from 5V (LT3420)

* Charges 100µF to 320V in 3.5 Seconds from 5V (LT3420-1)

* Charges Any Size Photoflash Capacitor

* Supports Operation from Two AA Cells or Any Supply from 1.8V to 16V

* Controlled Peak Switch Current:

* 1.4A (LT3420)

* 1.0A (LT3420-1)

* Controlled Input Current:

* 840mA (LT3420)

* 450mA (LT3420-1)

* Uses Standard Transformers

* Efficient Flyback Operation (>75% Typical)

* Adjustable Output

* Automatic Refresh

* Charge Complete Indicator

* No High Voltage Zener Diode Required

* No Output Voltage Divider Required

* Small 10-Lead MSOP Package

* Small 10-Lead (3mm × 3mm) DFN Package