UC3909DWTR

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PMIC – Battery Chargers: UC3909DWTR application field and working principle

The UC3909DWTR is a voltage-mode, pulse-width-modulated (PWM) controller integrated circuit (IC) especially designed for Lithium ion battery charging applications. It finds its use in charging of 1 Series (one cell) and multi-cell battery packs in applications, such as mobile phones, digital cameras, portable medical devices, DSC, PDA, and MP3 Players. As the switching frequency is adjustable from 40 kHz to 400 kHz, it is thus ideal for DC output isolated, point of load (POL) applications.

Application Field

The wide operating voltage range (1.5V to 20V) makes it suitable for high voltage applications. This device has been optimized for sensing charge current from the external current sense resistor directly, with no requirement for external transistors or switches. This feature provides extremely low cost solutions, high efficiency and open-loop system accuracy. Also, the large design flexibility of the on-time (T on ) and the off-time (T off ) makes it suitable for charging both cylindrical and prismatic battery packs.

Working Principle

This controller works by using a feedback loop. It senses the feedback input voltage and current to regulate the output voltage and current, respectively, so that charging can be carried out at a constant voltage and current. The charger output voltage is set through an external resistor divider, while the charge current is monitored by the internal current sense amplifier. When the voltage and current regulation is the desired value, a PWM signal is output which is used to drive a power switch, such as an external MOSFET.

The UC3909DWTR feature Automatic Mode Switching, which optimizes the cycle efficiency and current distribution between the two cells during multi-cell charging. This feature further results in increased battery life and better cell balance. The thermally enhanced MSOP-8 package and small size of this controller make it an ideal solution for space-constrained applications. Moreover, the undervoltage lockout (UVLO) feature allows for autonomously powering up the system, when the battery pack voltage is insufficient for charging, for instance during a low-battery or no-battery condition.

Conclusion

The UC3909DWTR controller is thus an ideal solution for a variety of space-constrained, high voltage applications. It is a cost-effective, efficient and accurate solution for Lithium ion battery charging.

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