engineers may often guess at what over- current level the protection IC will trigger its over-current protection. As for a higher standard of current sensing, it is becoming more common nowadays to make use of an external current sense resistor. Such resistor is available on the market and can be ordered with your preferred resistance value and accuracy
level. The great advantage of using this method is that the over-current threshold margin improves significantly in comparison to MOSFET current sense.
Thermal protection 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. The over-temperature threshold is specified by product version in a range from 40 to 70°C. 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 all internally fixed and do not need any external components, by selecting a particular product version one has the possibility to specify the required delay times. Another option is the 0V battery charge function, it is possible to prevent recharging when the battery voltage decreases below the 0V or deep discharge threshold (TYP. 1.25V). In such case, it would take a long time to recharge the battery and/or it may cause excessive heat dissipation. Refer to the datasheet for more details about optional functions.
Low current consumption 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-
www.cieonline.co.uk Components in Electronics September 2018 9
discharge rate of the battery pack. In normal operation, the current consumption is respectively 3.5µA and 2.5µA. When the product enters the standby mode, the product consumes only 0.04µA.
Conclusion
The R5441 and R5443 are welcome additions to the market; targeted devices are wearable devices with a small single cell Li-Ion or Li-Polymer battery. Both have a staggering small footprint of respectively 1.39 and 1.05mm2. The products offer a standard and enhanced safety solution with additional circuit for thermal protection to detect an overheated battery pack. Moreover, they have excellent high accuracy threshold settings providing a higher safety level for those applications that are worn on our body. We continue to develop more solutions for this market and we will be back soon with more news. Visit us at Electronica 2018 in München from 13 to 16 November at Hall C4, booth 441.
www.e-devices.ricoh.co.jp/en/
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