LTC4125 pin FuncTions STAT (Pin 8): Open Drain Status Pin. This pin pulls low the rectified peak voltage generated in the series LC tank when the part is delivering power. When connected to an and GND (see Applications Information). The voltage on LED, this pin provides a visual indicator that the LTC4125 is the FB pin is monitored during the transmit power search delivering power to a valid resonant receiver. The STAT pin to determine when the load requirements of the receiver is high-impedance during a fault condition or if no receiver have been met or exceeded. Short this pin to GND to dis- is detected during the most recent transmit power sweep. able the internal auto load detection feature. FTH (Pin 9): Frequency Threshold Input. This pin is used CTD (Pin 14): Transmit Power Search Delay Time Capacitor. to program the primary foreign object detection method. Attach a capacitor from the CTD pin to GND to program Connect this pin to the center tap point of a resistor di- the delay time between each cycle of an optimum transmit vider between IN and GND to set the maximum expected power search. Recommended delay times are typically 1s transmit LC resonant frequency value (see Applications or greater. See Applications Information for programming Information for programming details). A resonant driving instructions. Short to GND to stop search after the first frequency exceeding the programmed value indicates the cycle or leave open to default to a minimum delay time presence of a large conductive object in the field space (~20ms) between search intervals. generated by the transmit coil. Such a condition reduces EN (Pin 15): Enable Input Pin. Drive this pin above 1.22V the apparent inductance of the LC tank resulting in a higher (typ) to disable the AutoResonant driver. The SW1 and driving frequency. Transmitting into a foreign conductive SW2 pins default low when driver is disabled. Leave the object may result in TX power overload and/or exces- EN pin open or shorted to GND when disable function is sive heating of the foreign object. If a frequency fault is not used. detected, power delivery will immediately stop until the next transmit power search. GND (Pin 16, Exposed Pad Pin 21): Device Ground. Connect this ground pin to a suitable PCB copper ground PTH2 (Pin 10): Pulse Width Threshold Two Pin. The posi- plane for proper electrical operation and rated thermal tive pulse width waveform on the SW2 pin is proportional performance. to the voltage on this pin. IN2 (Pin 17): Input Supply Voltage: 3V to 5.5V. Supplies PTH1 (Pin 11): Pulse Width Threshold One Pin. The posi- power to the second half of the full bridge drivers. A local tive pulse width waveform on the SW1 pin is proportional 47µF bypass capacitor to GND is recommended on this pin. to the voltage on this pin. SW2 (Pin 18): Switch 2 Pin. This pin is the center node PTHM (Pin 12): Minimum Driver Pulse Width Input. The of the second half of the full bridge switches. Connect a voltage value on this pin determines the minimum driver series LC network between this pin and the SW1 pin for pulse width value used in the transmit power search. The full bridge operation. driver pulse width corresponds to transmit power. Shorting this pin to GND sets the pulse width of the first step in the SW1 (Pin 19): Switch 1 Pin. This pin is the center node of search to 1/32 of the natural period of the transmitting LC the first half of the full bridge switches. Connect a series LC tank. A faster transmit power search can be implemented network between this pin and the SW2 pin for full bridge when it is known that low transmit power (corresponding operation. Connect a series LC network between this to the 1/32 period pulse width) is not sufficient to meet pin and GND when only half bridge operation is desired. the requirements of the receiver load. Connect the pin to Maximum transmit power available is higher with full the center tap point of a resistor divider between IN and bridge operation. GND (See Applications Information) to program a larger IN1 (Pin 20): Input Supply Voltage: 3V to 5.5V. Supplies minimum pulse width. power to the first half of the full bridge drivers. A local FB (Pin 13): Resonance Feedback Voltage. Connect this 47µF bypass capacitor to GND is recommended on this pin. pin to the center tap point of a resistor divider between 4125f For more information www.linear.com/LTC4125 7 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Block Diagram Operation Applications Information Typical Applications Package Description Typical Application Related Parts
