Milpitas, Calif.—Linear Technology's LT3485 family integrates a complete photoflash capacitor charger, IGBT drive stage, and output voltage monitor in a 3-by-3 mm DFN package. The chip's control circuit is designed to allow the use of two very small "standardized" transformers (5.8-by-5.8-by-3 mm). No external components are required to set the output voltage. During charge, an output proportional to the photoflash capacitor voltage is available for monitoring. Input current is tightly controlled to provide consistent charge time.
The LT3485 works from a 1.8- to 10-volt input and thus can be powered by 2 AA alkaline cells or lithium-ion single or multiple cell batteries. The LT3485-3, -0, -2 and -1 have primary current limits of 2, 1.4, 1, and 0.7 amps, respectively (average input current is 700, 500, 350, and 225 mA, respectively). Corresponding charge time (3.6-volt input) is 2.5, 3.7, 5.5, and 4 seconds (first three versions specified for a 100 microfarad photoflash capacitor, the last for a 50 microfarad capacitor). The versions are otherwise identical.
Each device contains a high-voltage NPN power switch, which can withstand negative voltage on the switch pin without an external Schottky diode. The device's "charge" pin gives the user full control of the part. Driving the "charge" pin low puts the part in micropower shutdown. The "done" pin goes low on completion of the charging phase (pull-up resistor required).
Click here for the product datasheet. The LT3485 is priced at $2.25 each in 1k quantities and is available from stock.
Linear Technology, 1-800-4LINEAR, www.linear.com