Features

• 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

Typical Application

Description

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.