Power Over Ethernet (PoE)

PoE works by having a PoE capable injector or network switch. When the switch connects to a device, the switch tries to make a handshake with the device. The device has to have the signature to be able to do the handshake to activate PoE. Some Gateworks boards do not have this signature. If the signature is not detected, then power is not turned on.

PoE has evolved to define several different classes of power requirements:

• class 0 - (no signature) max device power of 12.95W
• class 1 - 4.0W available for max device power of 3.84W
• class 2 - 7.0W available for max device power of 6.49W
• class 3 - 15.4W available for max device power of 12.95W
• class 4 (PoE+) - 30W available for max device power of 25.5W
• class 5 (PoE++ type 3) - 60W available for max device power of 51W
• class 6 (PoE++ type 4) - 100W available for max device power of 71W

Please reference the user manual for the product to learn if it has POE capability at ​http://www.gateworks.com/usermanuals

Specs:

• 802.3af-2003 standard provides up to 15.4W of DC power (min 44Vdc and 350mA) to each device. Only 12.95W is assured to be available at the powered device (as some power is dissipated in the cable)
• 802.3at-2009 standard (PoE+) provides up to 25.5W of power and prohibits a powered device from using all four pairs for power. Some vendors have products that offer up to 51W by utilizing all four pairs.
• 802.3bt-2019 standard (PoE++) provides up to 51W of power (Type 3) and up to 71W (Type 4).

References:

• ​http://en.wikipedia.org/wiki/Power_over_Ethernet
• ​http://www.veracityglobal.com/resources/articles-and-white-papers/poe-explained-part-2.aspx

Gateworks PoE

Gateworks supports a variety of Power-over-Ethernet solutions depending on product family.

Family	Board	Supported	Notes
Venice	GW730x	802.3at class 5 (J20), Passive3 (J21)
	GW720x	802.3at class 4 (J17-A), Passive3 (J17-B)
	GW710x	Passive3 (J16)
Newport	GW650x	802.3at class 4 (J21), Passive3 (J22)
	GW640x	802.3at class 4 (J21), Passive3 (J22)
	GW630x	802.3at class 4 (J19), Passive3 (J20)
	GW620x	802.3at class 4 (J14), Passive3 (J16)
	GW610x	half-rectified3 Passive
	GW6903	full-rectified3 Passive
Ventana	GW540x	half-rectified3 802.3af (both ports)	Jumper1
	GW53xx	half-rectified3 802.3af (both ports)	Jumper1
	GW52xx	half-rectified3 802.3af	Jumper1
	GW51xx	half-rectified3 Passive
	GW552x	half-rectified3 Passive (both ports)
	GW5910	half-rectified3 802.3af	Jumper1
	GW5913	half-rectified3 802.3at

1. Jumper W1 selects passive (install) vs 802.3af (remove) voltage range
2. Half-rectified or Passive PoE on Gateworks boards assumes positive on blue pair, negative on brown pair. A cross-over cable can be used for devices using the opposite polarity

Passive PoE

Most Gateworks products support what is typically referred to as 'Passive PoE' as power is applied to the same pins defined in 802.3af however the intelligent signalling/detection is not present. We do this because 802.3af DC range is only 37-60V and our customers typically want lower ranges.

See the ​Gateworks Online Shop for Passive PoE Injectors

802.3af / 802.3at / 802.3bt

802.3af/at/bt are standards for intelligent Power Over Ethernet where a signature identifying a power class is required before the supply turns on voltage.

Gateworks boards with support:

• Venice GW730x: 802.3at class 5
• Venice GW720x: 802.3at class 4
• Newport GW640x/GW630x/GW620x: 802.3at class 4

802.3af and Auxillary power

When powering a board with both 802.3af and Auxiliary power (ie Vin barrel jack) at the same time it is a common mistake to believe you can switch back from Auxiliary supply to PoE and use Auxiliary as some kind of back-up supply avoiding a power cycle.

Most on-board 802.3af PoE controllers will drop their class negotiation with the PSE when not being used in order to conserve power budget. If this occurs this negotiation will need to be performed again if Auxiliary power goes away and the board will power cycle.

Half Rectified 802.3af

Originally, true 802.3af was costly and difficult to co-exist with passive PoE, so Gateworks designed a circuit that emulated it by providing the 'signature' needed to make an 802.3af PoE compliant switch enable power. The circuit used on the boards that use this emulation provides a 'class 0' signature but does not provide a 2-event class and PoE signature required for 802.3at. Additionally because it is only half-rectified it will not work on 802.3af switches and power adapters that use the opposite polarity.

While the 802.3 spec calls out the power pins explicitly it does not call out polarity because it also requires full rectification (which makes polarity a moot point). This created the fact that some products use one polarity and others use opposite with regards to + and - voltage rails (see here ​http://pinouts.ru/Net/poe_pinout.shtml). Some of our 802.3af products do not have this full rectification for space reasons which can make them in-compatible with PoE on some devices without the use of a 'cross-over cable'.

Refer to the table above to find which boards use half rectified 802.3af and note in the table that some of the above products feature a jumper 'W1' which enables 802.3af emulation ULVO (under voltage lockout). This jumper needs to be in the correct position (or removed) see above table depending on the board and whether or not you want passive PoE or 802.3af emulation.

The following switch products use the opposite polarity that Gateworks uses and thus requires either a) a fully rectified emulation (see above), b) a crossover cable, c) a ​GW16090 revB+:

• D-Link DGS-1008P
• Cisco SG100D-08P 8-port PoE switch
• ZyXel GS1910-24HP

GW16090 GigE 802.af/at to GigE passive PoE Adapter

The Gateworks GW16090 (​Purchase Here) allows boards that have no 802.3af/at support to be powered by an 802.3af/at switch or boards that only support 802.3af to be powered by an 802.3at switch. The GW16090 uses the Maxim MAX5969B PoE PD Interface Controller which provides both 802.3af and 802.3at signatures to the PSE device. For more info on the controler see: ​http://www.maximintegrated.com/en/products/power/switching-regulators/MAX5969B.html

The GW16090 is only intended with purely passive PoE Ethernet ports and is not meant to be compatible with ports with half rectified 802.3af or ports with true 802.3af/at and using it on those ports would be invalid and may need to unexpected results due to signature resistor conflicts.

For a list of products that the GW16090 has been validated with please see below.

Notes:

• Prior to revD only half rectification was supported.
• It is critical that any external connections (eth, jtag, serial, etc) to the product being powered by the GW16090 are electrically isolated. Otherwise ground-loops can occur causing power failure at the switch and possible board damage. This is particularly an issue with PoE switches that use Power/Ground polarity opposite of what Gateworks uses for Passive PoE.

Schematic Diagram of GW16090:

Isolation and Grounding Considerations

All of Gateworks PoE implementations are non-isolated which means the PoE ground will be tied to the boards digital ground. Full isolation requires a significant amount of space for the isolation transformer and adds in extra cost and complexity to the design.

Non-isolated designs are acceptable for deployments where the boards ground isn't exposed externally which effectively creates the isolation. In cases where the units ground will be tied into another instrument or supply, this can cause issues if there is a large differential between the switches ground and the unit. In these type of installations, an isolated PoE inserter/injector can be used to isolate the switch from the unit.

PoE PSE switches typically use high side switching which means the 48V DC output is always present and ground is switched on when the unit (PD - Powered Device) responds with a correct signature. Issues with this configuration can occur when powering multiple boards from the same switch if the boards share a common ground (for example they are mounted in metal cases and then mounted on a DIN rail or shielded Ethernet cables are used which then can create ground paths between the units). In these cases, with a common ground between the boards, if one board is turned on by the switch, the other board will then try to power on (or create a fault on the switch) since it will try to utilize the other units ground path. This type of condition can be eliminated if the boards can be isolated to not share grounds. Note this condition can even occur with a fully isolated implementation if the units have a common ground.

PoE Testing

Product	PoE Type	Notes
​Netgear FS108P 8port 10/100 802.3af PoE Switch	802.3af
​D-Link DGS-1008P 8port GigE 802.3af PoE Switch	802.3af	Opposite Gateworks Polarity1
​Cisco SG100D-08P 8port GigE 802.3af PoE Switch	802.3af	Opposite Gateworks Polarity1
​ZyXel GS1910-24HP 24port GigE 802.3af PoE Switch	802.3af	Opposite Gateworks Polarity1
​ANVISION 48V 0.8A 802.3af/at GigE PoE Injector	Passive	integrated power supply (despite advertised as 802.3af/at complient this is passive)
​TP-LINK TL-PoE150S 802.3af GigE PoE Injector 48V 0.35A	802.3af	external supply provided, not compatible with half-rectified 802.3af2
​Brash Networks BN-PE901G 802.3at GigE PoE Injector 52V 30W	802.3af/at	integrated power supply
​Ubiquiti Networks GP-A240-050G Passive GigE PoE Injector 24V 0.5A	Passive	integrated power supply
​GW10022 10/100 Ethernet Passive PoE Injector	Passive	requires external power supply, Discontinued
GW10027 Passive PoE Power Injector 24V 0.8A	Passive	integrated power supply, 10/100 only, Discontinued
GW10041 Passive PoE Power Injector 24V 2A	Passive	integrated power supply, 10/100 only, Discontinued
​GW10054 GigE Ethernet Passive POE Injector	Passive	requires external power supply

1. Requires cross-over cable if using with a Gateworks board on a port that has half-rectified passive PoE (ie Ventana)
2. This product is not compatible with the half rectified 802.3af used on certain Ventana products

PoE Output

Please note all PoE information on Gateworks SBCs and website pertain to PoE input to power the single board computer. There have been requests for Gateworks to offer PoE output to power something like an IP camera. There is usually a possibility of Gateworks modifying the SBC to allow for passive PoE output on the ethernet port that originally was designed for passive PoE input. This is achieved by reversing the protection diodes. Thus, the barrel jack input voltage would then be output through the passive PoE port in a passive fashion only. Active 802.3af output would not be provided.

Gateworks does offer PoE output on the GW16083 expansion board with the GW16104 ​here