30mW wireless receiver and constant current/constant voltage linear charger integrated
for compact wireless NiMH batteries

Linear announced the expansion of its wireless battery charging product line.

The compact wireless charging receiver announced this time (product name: LTC4123) is an integrated product combining a 30mW wireless receiver and a constant current/constant voltage linear charger for NiMH batteries such as Varta's power one ACCU plus series.

Through an external resonant LC tank connected with the LTC4123, the IC can receive power wirelessly from the alternating magnetic field generated by the transmit coil. The highly integrated power management circuit converts the coupled AC current into the DC current required for battery charging.

Wireless charging is possible even in completely sealed products, eliminating the need to constantly replace primary batteries. Through Zn-Air (Zinc-Air) detection functionality, the application allows interchangeable operation of rechargeable NiMH batteries and primary Zn-Air batteries using the same application circuit.

Both battery types do not require additional voltage conversion and can supply power directly to hearing aid ASICs. In contrast, 3.7V lithium-ion batteries require a step-down regulator along with the LTC4123's capability to supply power to the ASIC.

The LTC4123 can also accommodate 2.2V to 5V inputs by rectifying AC power supplied from the receiver coil and powering the complete functionality constant current/constant voltage battery charger. The charger's functions include charging current programmable up to 25mA, single-cell 1.5V battery charging voltage with ±0.5% accuracy, charge status indication, and onboard safety charge completion timer. Temperature-compensated charging voltage protects the NiMH battery and prevents overcharging. The LTC4123 prevents charging when the battery is inserted with reverse polarity and stops charging if the temperature becomes too high or too low.

The LTC4123 features a back metal pad for excellent thermal performance and is mounted in a compact low-profile (0.75mm) 6-pin 2mm x 2mm DFN package. This device is guaranteed to operate at grade E from –20°C to 85°C and is priced at $2.65 per unit based on 1,000 units.



Photo: Low-power wireless NiMH charger for hearing aids