基于A8735的超低功耗闪光灯充电方案

Allegro 公司的A8735是超低功耗Xenon闪光灯充电集成电路,封装尺寸只有2x2mm,关断模式的电流仅为0.5uA,峰值电流1A限制,效率大于75%,很适合用于手机单个锂离子电池充电以及小型照相机.本文介绍了A8735主要特性和优势, 功能方框图,典型应用电路图以及推荐的PCB布局图.

The Allegro® A8735 is a Xenon photoflash charger IC designed to meet the needs of ultra low power, small form factor cameras, parTIcularly camera phones. By using primary-side voltage sensing, the need for a secondary-side resisTIve voltage divider is eliminated. This has the addiTIonal benefit of reducing leakage currents on the secondary side of the transformer. To extend battery life, the A8735 features very low supply current draw (0.5 μA max in shutdown mode). The IGBT driver also has internal gate resistors for minimum external component count. The charge and trigger voltage logic thresholds are set at 1 VHI(min) to support applicaTIons implementing low-voltage control logic.

The A8735 is available in an 8-contact 2 mm × 2 mm DFN/MLP package with a 0.60 maximum overall package height, and an exposed pad for enhanced thermal performance. It is lead (Pb) free with 100% matte tin leadframe plating.

A8735主要特性和优势:

▪ Ultra small 2 × 2 DFN/MLP-8 package

▪ Low quiescent current draw (0.5 μA max. in shutdown mode)

▪ Primary-side output voltage sensing; no resistor divider required

▪ Fixed 1 A peak current limit

▪ 1V logic (VHI(min)) compatibility

▪ Integrated IGBT driver with internal gate resistors

▪ Optimized for mobile phone, 1-cell Li+ battery applications

▪ Zero-voltage switching for lower loss

▪ >75% efficiency

▪ Charge complete indication

▪ Integrated 50 V DMOS switch with self-clamping protection

图1.A8735功能方框图

图2.A8735单电源应用电路图

图3.A8735带单独偏压电源的应用电路图

图4.A8735推荐的应用电路图

图5.A8735推荐的元件布局图