Datasheet LTC4126-10 (Analog Devices) - 10

link to page 9 LTC4126-10
OPERATION
The LTC4126-10 is a low power battery charger with an inte- charge current begins to drop. The charge current continues grated step-down DC/DC converter designed to wirelessly to drop while the BAT pin voltage is maintained at the proper charge single-cell Li-Ion batteries and provide a 1.2V output charge voltage. This state of CC/CV charging is indicated by suitable for powering a hearing-aid ASIC. The part has three a slow blinking LED (typically 1.14Hz) at the CHRG pin. principal circuit components: an AC power controller, a full-fea- After the 3-hour charge termination timer expires, charg- tured linear battery charger, and a step-down DC/DC converter. ing stops completely. Once the charge cycle terminates, the LED at the CHRG pin stops blinking and assumes a
AC POWER CONTROLLER
pull-down state. To start a new charge cycle, remove the A complete wireless power transfer system consists of power source at ACIN or VCC and reapply it. transmit circuitry with a transmit coil and receive cir- cuitry with a receive coil. The LTC4126-10 resides on the
Automatic Recharge
receiver side, where an external parallel resonant LC tank After charging has terminated, the charger draws only connected to the ACIN pin allows the part to receive power 3.7µA (typical) from the battery. If it remains in this state wirelessly from an alternating magnetic field generated long enough, the battery will eventually discharge. To by the transmit coil. The Rectification and Input Power ensure that the battery is always topped off, a new charge Control circuitry (Figure 1) rectifies the AC voltage at the cycle automatically begins when the battery voltage falls ACIN pin and regulates that rectified voltage at the VCC below VRECHRG (typically 97.5% of the charge voltage). In pin to less than VCC(HIGH) (typically 5.5V). the event that the battery voltage falls below VRECHRG while the safety timer is still running, the timer will not reset. This
Operation without Wireless Power
prevents the timer from restarting every time the battery The LTC4126-10 can be alternately powered by connect- voltage dips below VRECHRG during a charging cycle. ing a DC voltage source to the VCC pin directly instead of receiving power wirelessly through the ACIN pin. Ground
Bad Battery Fault
the ACIN pin if a voltage supply is connected to VCC. If the battery fails to reach a voltage above VRECHRG by the end of a full charge cycle of 3 hours, the battery is deemed
BATTERY CHARGER
faulty and the LED at the CHRG pin indicates this bad battery fault condition by blinking fast (typically 4.58Hz). The LTC4126-10 includes a full-featured constant-current (CC)/constant-voltage (CV) linear battery charger with
Differential Undervoltage Lockout (DUVLO)
automatic recharge, automatic termination by safety timer, bad battery detection, and out-of-temperature- A differential undervoltage lockout circuit monitors the range charge pausing. Charge current is internally fixed differential voltage between VCC and BAT and disables at 10mA and the final charge voltage is pin-selectable via the charger if the VCC voltage falls to within 27mV (typical the V ΔV SEL pin to either 4.2V or 4.1V. UVLO) of the BAT voltage. This condition is indicated by a low on the ACPR pin. Charging does not resume until As soon as the voltage at the VCC pin rises 80mV (typical) this difference increases to 80mV at which time the ACPR above the BAT pin voltage, the charger attempts to charge the pin transitions back to high. The DC/DC must be enabled battery and a new charge cycle is initiated. A 3-hour charge for proper ACPR indication. termination timer starts at the beginning of this new charge cycle. When the VCC-to-BAT differential voltage rises above
Differential Undervoltage Current Limit (DUVCL)
150mV (typical), the charger enters constant-current (CC) The LTC4126-10 charger also includes differential under- mode and charges the battery at the full rated current of voltage current limiting (DUVCL) which gradually reduces 10mA. When the BAT pin approaches the final charge volt- the charge current from the full 10mA towards zero as the age, the charger enters constant-voltage (CV) mode and the VCC-to-BAT differential voltage drops from approximately Rev. 0 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Electrical Characteristics Pin Configuration Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Typical Application Related Parts