Linear Technology’s LTC4123 combines a 30-mW wireless receiver with a constant-current/constant-voltage linear charger for NiMH batteries. The device’s low-profile 2×2×0.75-mm package and low external component count make it well-suited for hearing aids and other low-power portable devices, such as smart cards and fitness devices.
An external resonant LC tank circuit connected to the LTC4123 enables the IC to receive power wirelessly from an alternating magnetic field generated by a transmit coil. Integrated power-management circuitry converts the coupled AC current into the DC current required to charge the battery. Wireless charging with the LTC4123 allows for a completely sealed product and eliminates the need to constantly replace primary batteries.
The LTC4123 rectifies the AC power from the receive coil and also accepts a 2.2-V to 5-V input to power the battery charger. An external programming resistor sets the charge current up to 25 mA, while a temperature-compensated charge voltage function protects the NiMH battery and prevents overcharging.