Wireless Power Receiver and Battery Charger LTC4120

Photocoupler

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The LTC4120 is a constant current / constant voltage wireless receiver and battery charger. Set up a charging current of up to 400mA with an external resistor. As shown in this schematic, if more than 400mA is required, two LTC4120 devices operating in parallel are used. In this case, the LTC4120 operates with a transmitter and a receiver coil and a rectifier. Simply connect the two LTC4120 inputs to the battery output and short the two DHC pins. Alternatively, you can choose to short the /CHRG and /FAULT flags to get a "line or" status flag. The operating frequencies of the two LTC4120s can be the same or different, and the LTC4120 with the lowest VFLOAT (matched in the feedback divider) is turned on first during recharging. Basic wireless transmitters require some improvements to support higher power levels. Simply adding the current capability of the two 68uH input bias inductors provides additional power. The demo board DC1968A uses two small TDK VLCF5028T-680MR40-2 inductors with 410mA saturation current and 400mΩ ESR. The two inductors were replaced with two TDK SLF10145T-680M1R2 inductors with 1.2A saturation current and 140mΩ ESR, resulting in a multiplier transmitter power level. The basic transmitter input supply is 5V ±5% and can deliver up to 1A. Charge the battery to 4.2V with a charge current of up to 800mA. The circuit can charge the battery at up to 3W and achieve an overall efficiency of approximately 60%.