Datasheet LTC4125 (Analog Devices) - 6

LTC4125
pin FuncTions IN (Pin 1):
Input Supply Voltage: 3V to 5.5V. Supplies during a power search, an internal comparator indicates power to the internal circuitry. A local 1µF bypass capacitor that the input current threshold has been exceeded, and the to GND is recommended on this pin. search is paused at this state until the next search interval.
CTS (Pin 2):
Transmit Power Search Settling Time The programmed input current threshold is determined Capacitor. Attach a capacitor from the CTS pin to GND using the following formula: to program the transmit power search settling time. RIN VITH RIN 0.80V Recommended settling times are typically between 1ms ITH = • = • R R R R and 20ms. See Applications Information for programming IMON IS IMON IS instructions. While not recommended, short to IN to disable If the voltage on the IMON pin exceeds 1.20V (VILIM, typ) the AutoResonant driver. at any point during the pause/delay time between the
IS– (Pin 3):
Input Current Sense Negative Input. Connect search intervals, an internal comparator indicates that a current sense resistor (R input current limit has been exceeded, the power delivery IS) between the supply volt- age and IS– using Kelvin Sense practices to monitor the is immediately stopped, and a new search interval is initi- input supply current. Tie this pin to the IS+ pin if no input ated. The programmed input current limit is determined current monitoring is desired. Refer to the Applications using the following formula: Information section for complete details. R V R 1.20V I IN ILIM IN LIM = • = •
IS+ (Pin 4):
Input Current Sense Positive Input. Connect RIMON RIS RIMON RIS this pin via an input current sense gain resistor (RIN) to the supply voltage connected to the R Short this pin to GND to disable the input current monitor IS sense resistor. This pin sinks a current proportional to the voltage across the feature. sense resistor (RIS) which is used to generate the IMON
NTC (Pin 6):
Thermistor Input. Connect a thermistor output (see Block Diagram): from NTC to GND, and a corresponding resistor from IN I to NTC. The voltage level on this pin determines if the I RIS • RIS IS+ = thermistor temperature is within an acceptable range. RIN The power delivery is stopped if the thermistor indicates Tie this pin to the IS– pin if no input current monitoring a temperature that is too hot. This feature may be used is desired. Refer to the Applications Information section to detect the presence of a foreign metal object or other for complete details. transmission fault. Once the temperature returns to the safe region, power delivery resumes. Refer to the Appli-
IMON (Pin 5):
Input Current Monitor. The IMON pin cations Information section for suggested usage. Leave sources a current that is proportional to the sense volt- this pin open to disable the temperature qualified power age across the sense resistor (RIS). With an output gain delivery feature. resistor (RIMON), the voltage on this pin is expressed as follows and corresponds directly to the input current (see
DTH (Pin 7):
Delta FB Threshold Input. This pin is used Block Diagram): to adjust the minimum detected power step size in the transmit power search to find the optimum transmitter I R V RIS •RIS IMON power operating point. The default setting (pin shorted to IIMON = •RIMON = • ΔVRIS RIN RIN IN) ensures proper operation in most systems. However, in very low power or very weakly coupled systems a Connect an appropriate capacitor in parallel with RIMON on smaller step size may be desired. Connect this pin to the this pin to obtain a time-averaged voltage representation center tap point of a resistor divider between IN and GND. of the input current (see Applications Information for more Please refer to the Operation and Applications Information details). If the voltage on this pin reaches 0.80V (VITH, typ) sections for more details. 4125f 6 For more information www.linear.com/LTC4125 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