Simplified Block Diagram
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- Charges Any Size Photoflash Capacitor
- 2.8s to Charge 100µF to 300V
- No Inrush Current
- High Accuracy Not Dependent on Transformer Turns Ratio
- Extends Battery Life with Input Voltage Monitoring
- Programmable Input Current Limit Up to 1.6A
- Robust Architecture Allows Use of Low-Cost Transformers
- Automatic Refresh Mode
- Charge-Done Indicator
- Small, 3mm x 3mm, 10-Pin TDFN Package
- Cell Phone Cameras
- Digital Cameras
- Film Cameras
- Personal Media Players
- Smartphone Cameras
The MAX8622 flyback switching regulator quickly and efficiently charges high-voltage photoflash capacitors. It is ideal for use in digital, film, cell-phone, and smartphone cameras that use either 2-cell alkaline/NiMH or single-cell Li+ batteries. An internal, low-on-resistance n-channel MOSFET improves efficiency by lowering switch power loss.
A current-limited, continuous-mode, transformer-switching scheme quickly charges the output capacitor. The cycle-by-cycle peak current-limit scheme has no inrush current. Current limit is programmable to control the maximum load drawn from the battery. An additional input-voltage monitor loop extends battery life by reducing the charge rate when the battery is nearly discharged. This also permits the current limit to be set for a faster charge rate under typical conditions, rather than a level dictated by the worst-case discharge state of the battery.
An open-drain DONE-bar output indicates when the photoflash capacitor is completely charged. The MAX8622 automatically refreshes the output every 11s, efficiently maintaining the capacitor charge level with minimum battery drain.
The MAX8622 provides high charge accuracy by using an external resistor-divider to monitor the output voltage. Sensing directly at the transformer secondary prevents output-capacitor discharge through feedback resistors while still providing direct output sensing for optimum voltage accuracy that is not transformer turns-ratio dependent. The MAX8622 is offered in a 3mm x 3mm 10-pin TDFN package.