ROHM Battery Charger IC: Charging Low-Voltage Rechargeable Batteries

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ROHM developed a battery charger IC, BD71631QWZ, designed to provide low-voltage charging of wearables like wireless ear buds and thin, compact IoT devices such as smart displays powered by rechargeable batteries.

In recent years the need for safer, higher density rechargeable batteries has led to the development of new battery types. This includes all-solid/semi-solid types models using novel materials for the electrode part and batteries that adopt different terminal compositions. However, many of the latest rechargeable batteries are small and thin, requiring low voltage charging in the 2V to 3V range. Moreover, there are currently no battery charger ICs that can handle a wide voltage range.

Based on this market demand, ROHM developed a battery charger IC that supports low voltage charging of not only li-ion, but also new types of rechargeable batteries such as all-solid and semi-solid state. The BD71631QWZ achieves low voltage charging over a wide range from 2.0V to 4.7V by improving the stability of the internal circuit.

Unlike general battery charger ICs that provide a fixed voltage, ROHM’s new product allows the charge voltage to be easily set by simply changing the external resistor, reducing design load when changing batteries. Additionally, original package technology results in a compact package just 0.4mm thickness, which is 60% lower than conventional products in market. This is contributing to smaller, thinner devices. In addition, each charging characteristic like charge/termination current can be set for CCCV charging, providing an optimal charging environment for thin, compact IoT and wearable devices utilizing the latest rechargeable batteries.

Going forward, ROHM will continue to contribute to providing greater application convenience by supplying more efficient charging solutions.

Key Features 

  • Compatible with new all-solid/semi-solid state rechargeable batteries requiring low voltage charging : The BD71631QWZ allows the charging voltage to be easily set from 2.0V to 4.7V by simply changing the external resistor, ensuring compatibility with not only single-cell li-ion batteries, but also all-solid/semi-solid and other new rechargeable battery types that demand low voltage charging.
  • Package size optimized for applications equipped with thin rechargeable batteries : ROHM’s new product utilizes original package technology to achieve a thin, compact 1.8mm × 2.4mm × 0.4mm form factor. As a result, mounting height has been reduced by 60% and footprint by 50% compared to standard products in a 3.0mm × 3.0mm × 1.0mm package. Ensuring that the height is the same as peripheral components contributes to smaller, thinner devices. This makes it particularly suitable for wearables and compact IoT devices equipped with ultra-thin sheet-like rechargeable batteries.
  • Achieves optimal CCCV charging according to the characteristics of the rechargeable battery : The BD71631QWZ enables the charge characteristics to be independently set, like charge current/voltage, termination current, recharge voltage for CCCV using an external resistor to achieve optimal charging based on the characteristics of rechargeable batteries. In addition, even if the battery needs to be changed during application design, it can be designed without reselecting components, reducing the number of workload required. Moreover, reducing the battery standby current down to 0μA in the standby state and incorporating various protection functions contributes to longer operating times in devices equipped with rechargeable batteries and improved safety during charging.

Application Examples

  • Devices equipped with low voltage and single-cell li-ion rechargeable batteries
  • Wearables such as wireless ear buds, electronic pens, e-cigarettes, etc.
  • Smart displays/tags and other compact IoT devices.

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