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P9025AC Datasheet(PDF) 10 Page - Integrated Device Technology |
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P9025AC Datasheet(HTML) 10 Page - Integrated Device Technology |
10 / 20 page 5W, QI WIRELESS POWER RECEIVER WITH INTEGRATED RECTIFIER AND LDO OUTPUT 10 09/01/15 P9025AC DATASHEET Advanced Foreign Object Detection (FOD) When metallic objects are exposed to an alternating magnetic field, eddy currents cause such objects to heat up. Examples of parasitic metal objects as such are coins, keys, paper clips, etc. The amount of heating depends on the strength of coupled magnetic field, as well as on the characteristics of the object, such as its resistivity, size, and shape. In a wireless power transfer system, the heating manifests itself as a power loss, and therefore a reduced power transfer efficiency. Moreover, if no appropriate measures are taken, the heating could be sufficient that the foreign objects may become heated to an undesirable temperature. During Power Transfer state, the receiver periodically will communicate to the transmitter the amount of power received by means of a Received Power packet. The transmitter will compare this power with the amount of power transmitted during the same time period. If there is a significant unexplained loss of power, then the transmitter will shut off power delivery, because a possible foreign object may be absorbing too much energy. For a WPC system to perform this function with sufficient accuracy, both the transmitter and receiver need each to account for and compensate for all of their known losses. Such losses could be to resistive losses, nearby metals that are part of the transmitter or receiver, etc. Because the system accurately measures its power and accounts for all known losses, it can thereby detect foreign objects owing to their creation of an unknown loss. The P9025AC employs advanced FOD techniques to both accurately measure its received power, and to accurately compensate all of its known losses. This compensation is implemented by means of a curve fitting table. This table supports up to 10 different curves stored in OTP (One Time Programmable) memory. The 10 programmed OTP settings are externally selected by means of the FOD1 selection resistor value (see page 14) which selects the settings that best match a particular system characteristic. Additionally, the I2C interface supports 1 volatile FOD compensation setting that can be selected that will override the OTP memory settings. A further enhancement is selected by the FOD2 offset resistor which adds a -300 to +300mW power offset to the values selected by the FOD1 resistor. This is useful to tune the selected compensation curve up or down to optimally match the actual known receiver system losses. For more information about how to determine and program the FOD settings, refer to application note AN-886 P9025AC FOD Tuning Guide. Over-Voltage Protection In the event that the input voltage increases above 15V, the control loop disables the LDO, and sends error packets to the transmitter in an attempt to bring the rectifier voltage below 7V. If the voltage at VRECT exceeds VOVP, two internal FETs turn on to clamp the AC inputs to quickly reduce the VRECT voltage. This is accomplished through loading the receiver resonant tank with extra capacitance shorted to ground through the above mentioned internal FETs. This changes the parallel resonance of the tank circuit which causes the Tx to Rx gain to decrease dramatically. The clamp is released when the VRECT voltage falls below the VOVP hysteresis level. VRECT must not be directly loaded. Over-Current Protection and Thermal Shutdown The P9025AC employs over-current and thermal protection by sending an End of Power packet to the transmitter when the output current reaches the current limit level or the die temperature exceeds the thermal shutdown level. The LDO output is also disabled during these conditions. The current limit level is programmable with an external resistor: For any value of RLIM below 25k , the output current is limited to 2-Amps. However, RLIM is not recommended to be set higher than 60 k Rectifier and VRECT Level Once VRECT powers up to greater than 7V, the full-bridge rectifier switches to half synchronous or full synchronous mode (depending on the loading conditions) to efficiently transfer energy from the transmitter to VRECT. The control loop of the P9025AC maintains the rectifier voltage between 5.45V and 7V, depending upon the output current (IOUT). The RLIM resistor sets both the current limit (ILIM) and the VRECT steps based on ISET which is a reference current used to partition the IOUT load range into 4 regions, each with a VRECT target for efficiency and transient optimization. ISET is equal to: The recommended value of RLIM for a 1A output is 30 k . I LIM 45000 R LIM --------------- = I SET 38000 R LIM --------------- = |
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