Ricoh launches two tiny Li-Ion protection ICs for wearable devices
Osaka, Japan, September 11, 2018 – Ricoh Electronic Devices Co., Ltd. in Japan has launched the R5441 and R5443 single cell Li-Ion battery protection ICs in a Wafer Level Chip Scaled Package (WLCSP). These ultra-small products are specifically designed for use in rechargeable smart watches, hearing aid instruments, fitness trackers, wireless earbuds and other small portable devices.
Wearable devices incorporate a small rechargeable Li-Ion battery with a capacity in the range from 50 to 100 mAh and have new challenging requirements for its internal components, like an ultra-small package size, low current consumption in on and standby mode but also sophisticated safety circuits. The R5441 and R5443 fully comply with these requirements. The R5443 is the smallest version and has a board space area of only 1.05 mm2. With a thickness of 0.36 mm, it is considered as one of the smallest single cell Li-Ion protection ICs available today. It is around 53% smaller compared to the popular protection ICs in a 1.4 x 1.4 mm DFN package.
Significant detail for the R5441 / R5443 is that the current consumption of the ICs is equal or lower than most other available solutions on the market and contributes reducing the self-discharge rate of the battery pack. In normal operation, the current consumption is respectively 3.5 µA and 2.5 µA. As soon the battery voltage decreases below the over-discharge voltage threshold, the product enters a standby mode and disables several internal circuits to lower the current consumption to 0.04 µA, ensuring further discharge of the battery is kept to a minimum.
Li-Ion batteries are safe in general when used according to the specifications but can become a potential hazard in case of an internal or mechanical malfunction. Overheating, emitting fumes or even worse can be the result; therefore, the protection IC monitors the charge and discharge process and interrupts as soon the process is at risk of going beyond the safe operation range of the battery cell. The following processes are monitored:
- Over-charge voltage: Battery voltage exceeds the charge threshold for a certain period.
- Over-discharge voltage: Battery voltage exceeds the discharge threshold for a certain period.
- Over-discharge current: Battery current exceeds the discharge threshold for a certain period.
- Over-charge current: Battery current exceeds the charge threshold for a certain period.
- Short current: Battery current exceeds the short discharge threshold for a certain period.
Both the R5441 and R5443 have an improved over-charge voltage threshold accuracy of ±10 mV versus ±30 mV for regular products. The idea behind this feature is to increase the charge voltage whilst maintaining the same safety level. As a result, the battery voltage will increase with 40 mV and extends the battery lifetime, which is important for applications with a small battery capacity.
Traditionally one makes use of the MOSFET on-resistance in order to measure the current flow of the battery pack. However, the on-resistance level is most inaccurate as it depends on various criteria such as ambient temperature, gate voltage and MOSFET type. In order to achieve a higher standard of current sensing, the R5441 and R5443 make use of an external current sense resistor. Such resistor can be ordered with your preferred resistance value and accuracy level. The great advantage of using an external resistor is that the over-current threshold margin improves significantly in comparison to the MOSFET current sense method.
The R5441 has an additional circuit to monitor the temperature of the battery pack by connecting an external NTC resistor to the Tin pin. In case of an over-temperature event, the charging or discharging process is interrupted. It is even possible to set different temperature threshold settings for the over-charge and over-discharge threshold.Optional functions:
- Optional latch and auto-release functions for the over-charge and over-discharge monitoring circuits are available. A latch function keeps the charge or discharge process interrupted until a load or charger is connected. The auto-release function releases the interruption at the same condition and when the release threshold is exceeded.
- Circuit delay times are fixed internally and do not need any external components.
- With 0V battery charge function, it is possible to prevent recharging when the battery voltage decreases below the deep discharge threshold. In such case, it would take a long time to recharge the battery and/or it may cause excessive heat dissipation.
R5441 R5443 Features:
|Absolute Maximum Rating||12 V|
|Supply Current at Normal Mode||Typ.3.5 μA|
|Standby Current||Max.0.04 μA|
|Over-charge Detection Voltage||4.2 V to 4.6 V (in 0.005 V step, ±10 mV)|
|Over-discharge Detection Voltage||2.0 V to 3.4 V (in 0.005 V step, ±2.0%)|
|Discharge Overcurrent Detection Voltage||0.015 V to 0.150 V
0.015 V to 0.050 V in 0.001 V step / 0.050 V to 0.150 V in 0.005 V step
0.015 V to 0.030 V: ±3 mV / 0.030 V to 0.050 V: ±10% / 0.050 V to 0.150 V: ±5 mV
|Charge Overcurrent Detection Voltage||-0.150 V to -0.015V
-0.030 V to -0.015 V in 0.001 V step / -0.150 V to -0.030 V in 0.005 V step
-0.020 V to -0.015 V: ±4 mV / -0.040 V to -0.020 V: ±20% / -0.150 V to -0.040 V: ±8 mV
|Short-circuit Detection Voltage||0.040 V to 0.280 V (in 5 mV step, ±5 mV)|
|Thermal Detection Temperature (R5443 only)||40°C to 70°C (in 5°C step, ±3°C)|
|Thermal Release Hysteresis Temperature (R5443 only)||0°C to 5°C (in 1°C step)|
|Over-charge Detection Delay Time||1.0 s|
|Over-discharge Detection Delay Time||16 / 32 / 128 ms|
|Discharge Overcurrent Detection Delay Time||8 /16 / 32 / 128 / 256 / 512 / 1024/ 3072 ms|
|Short-circuit Detection Delay Time||280 μs|
|Charge Overcurrent Detection Delay Time||8 ms|
|Thermal Detection Delay Time (R5443 only)||128 / 256 / 512 / 1024 ms|
|Thermal Release Delay Time (R5443 only)||128 ms|
|0 V-battery Charge Option||Available / Unavailable|
|Discharge Overcurrent Release Option||Auto Release Type / Latch Type|
|Package R5441 / R5443||WLCSP-8-P2 / WLCSP-6-P7|
|Dimensions R5441 / R5443||W1.51 x L0.92 x H0.36 mm / W1.25 x L0.84 x H0.36 mm|