Miniature wireless NiMH charger for hearing aids

December 23, 2015 | 12:01
Miniature wireless NiMH charger for hearing aids
Miniature wireless NiMH charger for hearing aids
Linear Technology has expanded its family of wireless battery charger ICs with the new LTC4123. This device combines a 30 mW wireless receiver with a linear constant current / constant voltage charger for NiMH batteries, such as the Varta Power One ACCU Plus series. Using an external LC resonant circuit, the LTC4123 can receive energy wirelessly from a magnetic field generated by a transmit coil. An integrated power management circuit converts the received AC voltage into DC for charging the battery.
 
The wireless charging capability of the LTC4123 allows hearing aids or other devices to be hermetically sealed and eliminates the need for periodic battery replacement. A zinc-air detection system makes it possible to use either rechargeable NiMH batteries or primary zinc-air batteries in the same device. Both battery types can provide power directly to the ASIC of a hearing aid, with no need for a voltage conversion stage.
 
A brief list of the LTC4123’s features: programmable charging current up to 25 mA, ±0.5% charging accuracy for a single 1.5 V cell, charge state indication, and an integrated safety timer for charge limiting. The charging voltage is temperature compensated to protect the NiMH battery against overcharging. The LTC4123 blocks charging if the battery is inserted with the wrong polarity and interrupts charging if the temperature is out of range. The LTC4123 is housed in a very compact, low profile (0.75 mm) 6-pin DFN package measuring 2 x 2 mm, with a metal pad on the rear for optimal thermal performance.
 
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