EVBUM2156 - Power-over-Ethernet PD Interface Evaluation Board
Contents
1. Auxiliary Support An auxiliary supply can easily be implemented with a diode Daux1 This auxiliary supply is often of a relatively low voltage e g 24 V However this implementation can result in variable behavior depending on which power source was connected first For example when the auxiliary is already connected when the Ethernet cable is plugged in the auxiliary voltage will interfere with the PoE detection and this will result in a dominant auxiliary supply However if the Ethernet cable is connected first the PoE detection will be successful and power will be drawn from the PoE interface even if an auxiliary supply is later connected It is often desirable for the device to always use the auxiliary supply even when PoE is available In that case the PoE must be disabled when the auxiliary is active This feature is available in the NCP1092 and NCP1094 Auxiliary support will disconnect the PoE supply when an auxiliary supply is connected by disconnecting the internal pass switch When not used the AUX pin of the IC should be connected to VPORTIN To configure the auxiliary Support dimension the resistor divider connected to the AUX pin so that the AUX pin voltage is higher than 3 1 V typ during desired operation The AUX pin has an internal pull down resistor of 100 KQ However such large resistance is not desired since a small leakage current can make the AUX voltage rise very quickly It is advised to add an ext2. before negotiating and applying power The detection signature is defined as the resistance between VPORTP and VPORTN and should be larger than 19 kQ and smaller than 26 5 kQ Typically a value of 24 9 kQ is used The PSE will measure this resistance by making at least two measurements of the current drawn by the PD while applying voltages between 2 8 and 10 V From these measurements the PSE will make a linear approximation from which it will extract the detection resistance This means that the total resistance seen at the input of the PD should be equal to 24 9 kQ During detection the DET pin is connected to ground so for the schematic of the evaluation board this means that Rouvioi T Ruyyio2 Rag 24 9 kQ For the detection and classification to succeed the total input capacitance of the PD should be limited to less than 150 nF When the input capacitance is higher the capacitor charge current will influence the detection resistance measurements and the detection signature will be invalid Under no circumstance is it allowed to connect the bulk input capacitor generally in the order of magnitude of 1 10 uF of the DC DC convertor to VPORTN The bulk input capacitor should always be located on the other side of the pass switch and the negative lead should be connected to RTN As such the bulk input capacitor will remain disconnected during detection and will not influence the detection signature Once the detection pha
3. the signal transformers must have a central tap to access the common mode voltage of each pair as these are the carriers for the PoE power Second care must be taken to select transformers that can support the dc common mode current required up to 350 mA for the IEEE802 3 af standard and 600 mA for the IEEE802 3 at standard without high losses It is recommended to choose magnetics that include common mode chokes to reduce electromagnetic emissions When board space is critical it can be interesting to choose connectors with build in magnetics MagJack These connectors also integrate the termination of the Ethernet line Contact your magnetics manufacturer for more information on magnetics suitable for PoE www BDTt com ON NCP1090GEVB NCP1094GEVB CON WE ca ae 01 D2 VEORTP MEBRAIBOTSG MBRAGOTSG T MB SMB z 11 oot ES Ei T0 Rbs1 R os D4 z MBRAIGOTSG MBRAIGOTSG EME SMB Shield T1 WE 744012011 Ds D VPORTP MB RAIGOTSG MBRAIGOT3G T ME EME oF os MBRAIGOTSG MBR AOT G SME EME CONS Tz WE 615008140171 WE 744012011 1 coo co oi oe one Chs2 i io H T ae ioc ie ioc ie ioc res 100 3 I vpORTR PORTE T T DearS perks Cline 1 Aine ONP 1ShMA63 A7T36 R 7 tats SMA OR Cbhs fens Shield Figure 5 Input Section of the Evaluation Boards Termination Termination of an Ethernet port should be done on the connector side of the magnetics The typical termination
4. must be validated for each customer application by customer s technical experts SCILLC does not convey any license under its patent rights nor the rights of others SCILLC products are not designed intended or authorized for use as components in systems intended for surgical implant into the body or other applications intended to support or sustain life or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application Buyer shall indemnify and hold SCILLC and its officers employees subsidiaries affiliates and distributors harmless against all claims costs damages and expenses and reasonable attorney fees arising out of directly or indirectly any claim of personal injury or death associated with such unintended or unauthorized use even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part SCILLC is an Equal Opportunity Affirmative Action Employer This literature is subject to all applicable copyright laws and is not for resale in any manner PUBLICATION ORDERING INFORMATION LITERATURE FULFILLMENT N American Technical Support 800 282 9855 Toll Free ON Semiconductor Website www onsemi com Literature Distribution Center for ON Semiconductor USA Canada P O Box 5163 Denver Colorado 80217 USA Europe Middle East and Africa Tech
5. INPUT SECTION Ethernet Connectors Magnetics and Termination Auxiliary Power Connector Ethernet Connector out Power over Ethernet Connector in Output Connector Figure 3 Connection Diagram The NCP109x evaluation boards have 2 RJ45 connectors One connector is used as the input connector and supports Power over Ethernet The power from this connector is split off to the NCP109x while the Ethernet data is passed through to the other RJ45 connector Please note that this second connector will not support Power over Ethernet When the Data Pair E Data Pair i Power Sourcing Equipment PSE I EDOOCE PLR LOOX sarar ED OXX Im output connector is connected to a proper Power over Ethernet PSE the PD detection will fail without damaging the board and no power will be applied When power is applied across the pairs of this second connector without negotiation the board will burn out the termination resistors Data Pair Data Pair Data Pair a a Data Pair Powered Device PD Figure 4 Ethernet Connection with Power over Ethernet Ethernet connections are double isolated which means the data passes through a signal transformer on both on the Power Supply Equipment PSE side as well as on the Powered Device PD side In the case that the port must support Power over Ethernet specific signal transformers must be selected First
6. NCP1090GEVEB NCP1094GEVB Power over Ethernet PD Interface Evaluation Board User s Manual ON Semiconductor http onsemi com EVAL BOARD USER S MANUAL Introduction The NCPIO90GEVB and NCP1094GEVB evaluation boards are designed to showcase the features of the NCP109x series of Power over Ethernet interfaces The boards are designed as splitter interfaces taking a PoE enabled port as input and offering the power to a separate connector while passing through the data to another Ethernet port The schematics gerber files and BOM of these boards are available through our website www onsemi com Basic Circuit Description The evaluation boards consist of different sections that will be described in detail in the next paragraphs First we will discuss the input section including selection of the correct connectors magnetics and the termination for a Power over Ethernet enabled connection In the next section we will explain the operation of the NCP109x the detection and classification process and how to configure the NCP109x for the correct power class Finally we will explain how to use the UVLO support for NCP1091 and NCP1093 or auxiliary support for NCP1092 and NCP1094 Table 1 ELECTRICAL CHARACTERISTICS NCP1090 NCP1091 NCP1093 NCP1092 NCP1094 Input Voltage PoE 37 V 57V Input Current PoE 680 mA eee AWN B D TIC com ON Pease October 2012 Rev o EVBUM2156 D NCP1090GEVB NCP1094GEVB
7. ailable for the DC DC convertor This is an open drain output that is active when the input capacitor has not completely charged yet The PGOOD pin is released to an external pull up when the voltage between RTN and VPORTN drops below 1 V typ The intended use for this signal is to connect the P OOD signal to the enable pin of your DC DC controller to ensure that the DC DC controller does not start operation before the input capacitor is fully charged On the evaluation board the PGOOD pin is connected to a LED Under normal operation this LED should only turn on briefly during startup and shutdown UVLO Support All NCP109x ICs have internal UVLO capability and will disconnect the pass switch when the VPORTP voltage becomes too low The threshold for this is set by an internal resistor divider to VUVLO on 37 V typ and VUVLO off 31 V typ In addition the NCP1091 and NCP1093 allow externally programming the threshold to a different value If you want to continue using the default UVLO threshold with the NCP1091 or NCP1093 connect the UVLO pin to VPORTN To enable under voltage lockout with a different threshold you must populate the resistor divider created by Ruvlol and Ruvlo2 This can only be done on the NCP1091 or NCP1093 The values for these components can be calculated as follows V 1 2 V Riviot Rito uvlo on R uvlo2 Take also into account that the UVLO resistors will influence the detection resistance
8. ernal pull down resistor of 10 KQ From this we can dimension Raux1 as follows lao Root ss i 10 kQ When the voltage on the AUX pin rises above 3 1 V the NCP109x will disable the PoE detection circuit and disconnect the pass switch as well as release PGOOD To connect the auxiliary support and have priority of the auxiliary supply on the evaluation boards you must connect the jumper J1 This is only possible if your evaluation board has an NCP1092 or NCP1094 To get an efficient system it is desirable to have the forward voltage drop over the auxiliary diode Daux1 as low as possible especially since the auxiliary power supply is often of lower voltage and therefore has less headroom for voltage drop This requires a schottky diode However schottky diodes at higher voltages often have a large reverse leakage current up to as much as 10mA If this current were www BDTt com ON NCP1090GEVB NCP1094GEVB to flow through the auxiliary resistor divider the AUX pin we put a PMOS transistor Q1 in series which will disable voltage would rise above the threshold and turn of the PoE this current path The resulting schematic is shown in even when no auxiliary supply is available For this reason Figure 9 Daux1 MBRD5H100T4G DPAI 3 PORTP Daux2 CON1 BZX84C10LT1 DC10A SOT23 Q1 NTR0202PL 50T23 J1 JUMPER1 Raux1 an Figure 9 Auxiliary Supply Circuit nClass_AT To signal if the PSE went through the 2 event class
9. for Ethernet ports is called a Bob Smith termination and is shown in Figure 6 For ports that are Power over Ethernet this termination network should be modified to block the DC common mode voltage between pairs from creating a large current through Bhsk Phed Phe Phe the termination resistors which would blow up the fas eas bane feos termination resistors This is done by inserting 10 nF blocking capacitors in series with the termination resistors bee The modified termination network is shown in Figure 7 1000p Cha pair 1 i F Figure 7 Modified Bob Smith Termination Rectification and Protection Power applied to the Ethernet pairs has no defined polarity and thus needs to be rectified by diode bridges The diode selection is important for the total efficiency of the system as the forward voltage drop of the diode can be quite large For this reason discrete schottky diodes are a common choice for the rectification bridge To comply with ESD protection guidelines a TVS should be added to the rectified power lines In the evaluation boards the ISMAS58AT3G was selected for this part www BDTt com ON Figure 6 Bob Smith Termination NCP1090GEVB NCP1094GEVB NCP109x OPERATION Power over Ethernet Detection and Classification To distinguish power over ethernet enabled ports from regular Ethernet ports the Power Supply Equipment PSE will first check the detection signature of the Powered Device PD
10. ification The NCP1093 and NCP1094 are capable of classifying as and the full 25 5W is indeed available the NCP1093 and class 4 as per the 802 3at standard delivering up to 25 5 W NCP1094 offer the nClass_AT signal This pin has an open If the PD is connected to a PSE complying with the drain output that is pulled low when two classification 802 3af standard the PSE will apply power after one events have occurred classification event but this power will be limited to 13 W ON Semiconductor and WwW are registered trademarks of Semiconductor Components Industries LLC SCILLC SCILLC owns the rights to a number of patents trademarks copyrights trade secrets and other intellectual property A listing of SCILLC s product patent coverage may be accessed at www onsemi com site pdf Patent Marking pdf SCILLC reserves the right to make changes without further notice to any products herein SCILLC makes no warranty representation or guarantee regarding the suitability of its products for any particular purpose nor does SCILLC assume any liability arising out of the application or use of any product or circuit and specifically disclaims any and all liability including without limitation special consequential or incidental damages Typical parameters which may be provided in SCILLC data sheets and or specifications can and do vary in different applications and actual performance may vary over time All operating parameters including Typicals
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12. or a class 4 PD is shown in Figure 8 UVLO_on f 2nd Mark Event ev CNN 5 4 V Reset Range OV Operation Mode Number of Mark Event PSE Type identification 2 Fingers Classification with Mark Events at spec Power On PSE identified as type 2 PSE at PSE identified by default as tvpe 1 PSE af Figure 8 PD Classification for Class 4 www BDTt com ON NCP1090GEVB NCP1094GEVB Inrush and Operational Current Limitation When the PSE applies power to the PD after the detection and classification phases the pass switch will initially limit the current passing through it In this way large currents caused by the DC DC convertor input capacitor charging are prevented When the voltage over the pass switch drops below the limit value this indicates that the bulk capacitor is charged Table 3 PD INPUT CURRENT LIMITS The pass switch is then turned completely on and the IC switches to an operational current limit Both limits are programmed with the same programming resistor which is connected to ILIM Programming resistors should be placed as close to the IC as possible to minimize noise Typical values for this programming resistor are shown in Table 3 Average Input Power of the PD Recommended ILIM Resistor Inrush Current Limit Operational Current Limit 25 5 W 169 kQ 120 mA 680 mA PGOOD Indication The NCP109x provide a PGOOD signal to indicate when the power is av
13. se is passed the NCP109x will disconnect the DET pin to save power that would otherwise be dissipated in the detection resistor 20 5 V ist Class Event ist Mark Event 2nd Class Event Class range syv ON When the PSE has detected a valid PD signature the PSE will start the classification phase During the classification phase the PSE will determine the power class of the PD This is determined by measuring the current drawn when a voltage pulse of typically 17 5 V is applied Class 4 is only valid in 802 3at In 802 3af class 4 is defined as reserved and treated as class 0 So to make sure that the PD can distinguish between at type PSEs applying 25 5 W for class 4 and af type PSEs applying 13 W for class 4 the classification pulse is repeated by the at type PSE when the PD is programmed for class 4 This difference is made visible to external components through the nClassAT pin The power class can be programmed by setting the classification resistor to the correct value Programming resistors should be placed as close to the IC as possible to minimize noise The different power classes and their corresponding classification resistors are listed in Table 2 Table 2 PD POWER CLASSIFICATION Average Input Power of the PD Classification Power Class Resistor Only for NCP1093 NCP1094 After the PSE has detected a valid power class for the PD it will apply the full power to the PD A typical classification sequence f
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