P9025AC FOD Tuning Guide APPLICATION NOTE
●Introduction:
■The P9025AC wireless power receiver is a WPC-compliant integrated circuit used to receive wireless power inductively. To achieve WPC compliance, the Foreign Object Detection (FOD) feature must be enabled and tuned on both the transmitter (Tx) and Receiver (Rx).
■In any wireless power transfer system where a magnetic field is induced to transfer energy, the power transfer flux is also present outside the Tx and Rx coils. Although this field decays proportionally to the inverse square of the distance, it is typical that these fields intersect with other permeable materials (such as copper, steel or Lithium Ion batteries). These ferrous materials that are unrelated to the power transfer but necessary to the product, absorb a portion of the transmitted energy and appear as a systemloss in efficiency. Other ferrous objects that are not part of the system may also be present, such as keys, coins, or other foreign objects - and they too may absorb energy during operation. As a safety precaution, the Tx will disable power transfer whenever the losses are measured to be higher than a pre-determined threshold.
■Most wireless power systems will have some permeable materials present by design on the Tx and Rx side of the system (such as the final product casing). This is normal and can be accounted for by tuning the FOD parameters of the system. The P9025AC has internal OTP registers that are used to configure the FOD parameters required to ignore losses from known system design objects and only report losses associated with actual foreign objects. Additionally, the P9025AC offers an external global FOD offset adjustment resistor from FOD2 pin to GND. This resistor can add a positive or negative offset to the reported power by the device based on the pre-programmed FOD curve.
■For WPC-compliant systems, the loss allowed due to foreign objects is 350 mW, not including known losses due to the Tx and Rx systems. For systems where WPC compliance is not a requirement, FOD can be programmed to accept losses greater than 350 mW, or can be disabled completely.
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P9025AC 、 P9038 、 P9025AC-R 、 P9025AC-RNDGI 、 P9025-R-EVK 、 P9025AC-R-EVK |
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Application note & Design Guide |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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08/26/15 |
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REVISION 08/26/15 |
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AN-886 |
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858 KB |
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