Datasheet LTC4126 (Analog Devices) - 8

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PIN FUNCTIONS NTC (Pin 1):
Thermistor Input. Connect a thermistor from
CHRG (Pin 6):
Open-Drain Charge Status Output Pin. This NTC to GND, and a bias resistor from VCC to NTC. The volt- pin can be pulled up through a resistor and/or an LED to age level on this pin determines if the battery temperature indicate the status of the battery charger. This pin has is safe for charging. The charge current and charge timer four possible states: slow blink to indicate charging, fast are suspended if the thermistor indicates a temperature blink to indicate a fault, pulled down to indicate charging that is unsafe for charging. Once the temperature returns done, and high impedance to indicate no input power. To to the safe region, charging resumes. Ground the NTC pin conserve power, the pull-down current is limited to 300µA. if temperature qualified charging is not needed.
ACIN (Pin 7):
AC Input Voltage Pin. Connect the external
EN (Pin 2):
Digital Logic Input Pin to Enable the DC/DC LC tank, which includes the receive coil, to this pin. Con- Converter. A minimum voltage of 1.1V enables the regula- nect this pin to ground when not used. tor provided that the LTC4126 is not in battery disconnect
BAT (Pin 8):
Battery Connection Pin. Connect a single-cell mode (see Battery Disconnect/Ship Mode under Operation Li-Ion battery to this pin. Whenever enough input power section). A low voltage (0.4V max) disables the regulator (AC or DC) is available, the battery will be charged via this and allows the pushbutton to control it. If only pushbut- pin. Additionally, the DC/DC Converter is powered from ton control is desired, tie this pin to ground. Tie this pin the battery via this pin. To minimize the effect of switching to BAT if the DC/DC needs to remain enabled all the time. noise from the DC/DC converter on charger performance, Do not leave this pin unconnected. this pin should be decoupled with a 1µF capacitor to GND
PBEN (Pin 3):
Pushbutton toggle input pin to enable/disable if the DC/DC converter is enabled while charging. the DC/DC converter. Enabling of the regulator can only
STAT2 (Pin 9), STAT1 (Pin 10):
Digital CMOS Logic Status occur if the LTC4126 is not in battery disconnect mode (see Output Pins. The low level of these pins is referenced to Battery Disconnect/Ship Mode under Operation section). GND and the high level is referenced to V A weak internal pull-up forces PBEN high when not driven. OUT. Consequently, these indicators are not available if the DC/DC is disabled. A normally open pushbutton is connected from PBEN to These two pins together with ACPR indicate the various ground to force a low state on this pin when the button charging states and fault conditions. However, when no is pushed. However, the pushbutton is ignored if the EN input power is available and the DC/DC converter is enabled, input is high. If the pushbutton function is not needed, these pins instead indicate the voltage level of the battery. leave this pin unconnected.
V V CC (Pin 11):
DC Input Voltage Pin. An internal diode is
SEL (Pin 4):
Digital Logic Input Pin to Select the Battery connected from the ACIN pin (anode) to this pin (cathode). Charge Voltage. A logic high on this pin selects 4.35V and When an AC voltage is present at the ACIN pin, the voltage a logic low on this pin selects 4.2V. Do not leave this pin on this pin is the rectified AC voltage. When the ACIN pin unconnected. is not used (or shorted to ground), connect this pin to a
ACPR (Pin 5):
Digital CMOS Logic Output Pin to indicate DC voltage source to provide power to the LTC4126 and if there is enough input power available to charge the bat- charge the battery. tery. This pin goes high when the VCC-to-BAT differential
OUT (Pin 12):
DC/DC Converter Output Pin. This pin pro- voltage rises above 80mV (typical) and goes low when the vides 1.2V to power hearing aid ASICs. A low ESR ceramic differential voltage drops below 27mV (typical). The low capacitor of at least 2.2μF should be placed close to this level of this pin is referenced to GND and the high level pin to stabilize the converter. is referenced to the OUT pin voltage. Consequently, this indicator is not available if the DC/DC is disabled.
GND (Exposed Pad Pin 13):
Ground Pin. The exposed pad on the backside of the package must be soldered to the PCB ground for a low-resistance electrical connection as well as for optimum thermal performance. Rev. 0 8 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