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2017-09-02 03:40  
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The RTL8201BL is a single-port Phyceiver with an MII (Media Independent Interface)/SNI(Serial Network Interface). It implements all 10/100M Ethernet Physical-layer functions including the Physical Coding Sublayer (PCS), Physical Medium Attachment (PMA), Twisted Pair Physical Medium Dependent Sublayer (TP-PMD), 10Base-Tx Encoder/Decoder and Twisted Pair Media Access Unit (TPMAU). A PECL interface is supported to connect with an external 100Base-FX fiber optical transceiver. The chip is fabricated with an advanced CMOS process to meet low voltage and low power requirements.


3.3V power supply and voltage conversion circuit

 RTL8201BL is fabricated in 0.25um process. The core circuit needs to be powered by 2.5V , however, the circuit of digital IO and DAC need 3.3V power supply. RTL8201BL has embedded a regulator to convert 3.3V to 2.5V. Just like many commercial voltage conversion devices, The 2.5V output pin(PWFBOUT) of this circuit requires the use of an output capacitor(22uF tantalum capacitor) as part of the device frequency compensation and another small capacitor(0.1uF) for high frequency noise de-coupling. And PWFBIN is fed with the 2.5V power from PWFBOUT through a ferrite bead as below figure shown. Strongly emphasize here, could not provide external 2.5V produced by any other power device for PWFBOUT and PWFBIN. The analog and digital Ground planes should be as large and intact as possible. If the ground plane is large enough, the analog and digital grounds can be separated, which is a more ideal configuration. However, if the total ground plane is not sufficiently large, partition of the ground plane is not a good idea. In this case, all the ground pins can be connected together to a larger single and intact ground plane.RTL8201BL