Ethernet Switch IC Uplinks: What “5+2” and “8+2” Really Mean, RGMII Levels and the 1.1 V Core Rail | VOOHU

Most switch-IC enquiries start the same way: "I need an 8-port switch." Port count alone almost always leads to a re-spin, because what decides whether the board can actually be routed is not how many copper ports there are. It is what the "+1" or "+2" after the number actually is, what logic level it runs at, and whether it matches the CPU or optical module on the other side.

This article is not a full switch design guide (we covered the unmanaged switch solution separately). One thing first: the JL5xxx and JL6xxx switch ICs below are JLSemi products, and VOOHU is their distributor. Every figure here comes from the VOOHU product pages. The focus is the four things that usually surface only at prototype stage — uplink ports, interface levels, the core supply rail and temperature grade — across the 20 order codes we carry.

1. Read the port count properly: 5 and 5+2 are not the same part

JLSemi switch ICs use two notations for port count: a plain number (5, 8) and a number with a plus sign (3+1, 5+1, 5+2, 8+1, 8+2). The difference matters.

A plain 5 or 8 means the device integrates that many complete Ethernet ports, with both MAC and PHY on chip. On the schematic you see five or eight differential pairs going straight through a LAN transformer to the RJ45. There is no external MAC interface at all.

In 5+2, the 5 are copper ports with integrated PHY, and the 2 are expansion or uplink ports. Those are not copper ports. They are MAC-side interfaces (MII, RMII, RGMII) or SerDes lanes (SGMII, H-SGMII) brought out of the die. You can use them to attach a CPU, drive an external PHY, feed an optical module, or cascade a second switch IC for more ports.

So "an 8-port switch" can be built two completely different ways: with an 8 device such as JL5108C-NC, or with an 8+2 device such as JL5110C-NC. The first is a closed eight-port box. The second keeps two uplinks free for a CPU or an upstream link.

2. What "Interface Mode = NA" rules out

The published parameter table has a field called Interface Mode. When it reads NA, the device has no external MAC or SerDes interface, and three things become impossible:

First, no CPU attachment. Without MII, RMII or RGMII there is no path for an MCU or SoC to exchange frames with the switch, so gateways, PLCs and data concentrators are out. The part can only serve as a pure forwarding, unmanaged switch.

Second, no optical port. A fibre link needs SerDes (1000Base-X). Any part whose Interface Mode is NA also shows NA in the Optical Port field.

Third, no cascading. Two switch ICs have to be joined through a MAC interface or SerDes. With NA, the port count you see is the hard ceiling.

Four families among them are NA: JL5105C (5-port 100M), JL5108C (8-port 100M), JL6105-NC (5-port 1G) and JL6108-PC (8-port 1G). These are the drop-in unmanaged parts: lowest cost and smallest area, with no headroom.

3. Uplink to a CPU: choosing MII, RMII or RGMII, and the level trap

An uplink to a CPU simply presents one switch port as a MAC interface wired to the host MAC. The three common options differ in pin count and bandwidth.

MII uses 4-bit data with a 25 MHz reference clock, caps out at 100 Mbps and needs the most pins. RMII uses 2-bit data with a single 50 MHz clock, has the same 100 Mbps ceiling but roughly half the pins, and is the mainstream choice for fast Ethernet designs. RGMII uses 4-bit data clocked on both edges at 125 MHz, reaches 1000 Mbps, and is the only option for a gigabit uplink.

One point is easy to miss: the whole 100M family (JL5104C, JL5106C, JL5109C, JL5110C) lists only MII and RMII, never RGMII. The uplink on a fast Ethernet switch IC therefore cannot exceed 100 Mbps. If the design needs a gigabit uplink, it has to be a JL6 device.

The second trap is the RGMII IO level. The published MAC interface voltage field is exactly that level.

The JL6107-PC family lists 1.8 V, 2.5 V and 3.3 V, so all three are supported. JL6110-PC lists 3.3 V only. Most current SoCs drive RGMII at 1.8 V or 2.5 V, so pairing a JL6110 with a 1.8 V RGMII host cannot be a direct connection: it needs level translation, or a different part. Nothing on the schematic reveals this, and it usually shows up only when the first boards fail to link, so check the IO level at both ends during selection.

The 100M family is uniformly 3.3 V on the MAC interface. A 3.3 V RMII host is fine; a 1.8 V host is not.

4. Fibre uplinks: only three types actually support 1000Base-X

An SFP uplink requires SerDes with 1000Base-X support. Of the 20 order codes we carry, only three types (six order codes) show anything other than NA in the Optical Port field:

Note the non-S parts, JL6107-PC and JL6107-PI. Same 5+2 port count, but the interface mode stops at RGMII and the optical port is NA. Within one JL6107 family, the S suffix alone decides whether a fibre uplink is possible. Reading only "5+2" off a selection table makes these look interchangeable, so check the full suffix before ordering.

On SGMII versus H-SGMII: SGMII is the standard 1.25 Gbps serial interface, one SerDes lane per gigabit port. H-SGMII is a higher-rate variant, typically used for 2.5G uplinks or multi-port multiplexing. Whether your optical module and the far-end device support it has to be confirmed against their datasheets.

5. Power tree: is the 1.1 V core rail external or generated on chip?

This item has the most direct effect on hardware workload. The published External supply voltage field uses two different notations.

Listed as "1.1 V; 3.3 V": JL6105-NC, JL6107-PC, JL6107-PI, JL6108-PC, JL6110-PC and JL6110-PI. Two external rails are required, so the 1.1 V core needs its own DC-DC converter.

Listed as "3.3 V (1.1 V)¹": the entire 100M family, plus the four JL6107S and JL6107SC order codes. This notation carries a footnote marker whose body is not expanded on the parameter page, so confirm the meaning against the datasheet for that order code. It normally indicates a single 3.3 V input with the 1.1 V rail generated internally.

The practical consequence: moving from JL6107-PC to JL6107S-PC inside the same family adds fibre capability and changes the supply notation at the same time. Both affect BOM and layout, so do not substitute on matching port count alone. Before drawing the power tree, get the datasheet for the exact order code and settle whether the 1.1 V rail is external or internal. That step cannot be skipped.

6. Commercial or industrial: -NC/-NI, -PC/-PI, and which parts have no industrial version

The suffix rule is simple. The 100M family uses -NC (commercial, 0~70℃) and -NI (industrial, -40~85℃). The 1G family uses -PC and -PI.

What matters is not the suffix itself but this: not every type has an industrial version. Based on the order codes currently listed, the parts below are commercial-only.

The value of this table is in the ordering of decisions. For an industrial gateway, a PLC expansion module or an outdoor cabinet that must hold -40~85℃, start by narrowing to types that have an industrial order code, rather than choosing on port count and discovering later that no industrial part exists. The gap that catches people most often is an 8-port fast Ethernet device with an uplink: neither JL5109C nor JL5110C has an -NI version, so the usual answers are dropping to 5+1 with JL5106C-NI or moving up to gigabit with JL6110-PI.

One more caution. A commercial part that "works" at -20℃ on the bench is not the same as a part qualified for production. The temperature grade is the range over which the vendor guarantees the datasheet parameters. Outside it, nothing is guaranteed, and lot-to-lot spread, PLL lock at low temperature and auto-negotiation timing can all drift. A couple of boards passing in the lab does not substitute for that guarantee.

7. Package and board area: QFN48 to TQFP176 is an 11x difference

Port count drives package size directly, and that decides whether the board can absorb the part.

Two notes. First, these are exposed-pad packages. A multi-port gigabit switch runs warm at full load, so the thermal via array under the pad is not optional, and the copper under it should not be cut through by routing. Second, JL6108-PC shares the LQFP128 name with JL6107 but measures 20*14 mm rather than 14*14 mm. It is a different PCB footprint, so the library has to be redrawn rather than reused.

8. Full selection tables

The two tables below hold the complete published parameters for all 20 order codes, as listed on the VOOHU product pages. Copper port capability is 10Base-T / 100Base-TX on the 100M family, and 10Base-T / 100Base-TX / 1000Base-T on the 1G family.

8.1 Fast Ethernet family (JL5xxx)

Optical port is NA across the whole 100M family, and external supply is listed as 3.3 V (1.1 V)¹ throughout.

8.2 Gigabit family (JL6xxx)

"+SGMII, H-SGMII" means those two are supported in addition to MII, RMII and RGMII.

9. A three-step method and a pre-prototype checklist

Compressed into an order you can actually follow:

Step one, fix the temperature grade. Does the design need -40~85℃? If so, narrow the field first to types that have an -NI or -PI order code (JL5104C, JL5105C, JL5106C, JL5108C, the whole JL6107 family, and JL6110), then carry on. Doing this first avoids starting over later.

Step two, fix the uplink. Ask three questions: does it attach to a CPU, does it need fibre, does it cascade to a second switch? A yes to any one of them eliminates every part whose interface mode is NA. Fibre leaves only JL6107S, JL6107SC and JL6110. A gigabit uplink eliminates the entire 100M family.

Step three, only now pick copper port count and package. Two or three candidates usually remain, and port count, board space and cost decide between them.

10. Frequently asked questions

Q1. For an 8-port gigabit switch, JL6108-PC or JL6110-PC?

It depends on the uplink. For pure eight-port forwarding with no CPU and no fibre, JL6108-PC is smaller and simpler. If a host processor or a fibre uplink is involved, it has to be JL6110 (8+2, SGMII and H-SGMII, 1000Base-X). Note also that JL6108-PC has no industrial version, so an industrial design goes straight to JL6110-PI.

Q2. What is the difference between JL6107-PC and JL6107S-PC, and can they be swapped?

Not directly. Both are 5+2 in LQFP128 14*14 mm, but the S part adds SGMII, H-SGMII and a 1000Base-X optical port, and its external supply is listed differently (1.1 V; 3.3 V versus 3.3 V (1.1 V)¹). Choose the S part when fibre is needed, and re-check power tree and pin assignment against each datasheet when substituting.

Q3. The switch IC already integrates the PHY. Is a LAN transformer still needed?

Yes. What is integrated is the PHY transceiver, not the isolation. The copper interface still needs a LAN transformer for galvanic isolation and common mode rejection: a 2-pair device for 100M, a 4-pair device for gigabit. An RJ45 with integrated magnetics combines the two into one part.

Q4. Interface mode says RGMII, so why does the board not reach gigabit?

First separate copper ports from the uplink. The copper ports on a JL5 device are 10/100Base-TX by definition and the interface mode never lists RGMII. If a gigabit uplink underperforms, check three things first: whether the RGMII IO level is identical at both ends, whether the RGMII internal delay configuration matches, and whether the 1.1 V core rail has come up correctly.

Q5. Why do some types list 8 ports and others 8+2, with a noticeable price gap?

An 8 is a closed eight-copper-port device with no external interface. An 8+2 adds two configurable uplinks, which means extra SerDes and MAC interface logic on chip and a much larger package (QFN88 versus TQFP176). The price difference buys expansion capability, not two more RJ45 jacks.

Q6. Must an industrial project use industrial parts, or can a commercial part be derated?

The temperature grade is the guaranteed parameter range in the datasheet, not a measured limit. One commercial sample passing at -20℃ says nothing about whether every unit in volume will meet auto-negotiation, PLL lock and eye diagram limits under the same conditions. If the project calls for -40~85℃, select from the types in section 6 that have an industrial order code.

If a selection or a cross-reference is unclear, send us the host processor, the RGMII or RMII level, the port count required and the temperature grade, and the VOOHU engineering team will come back with matching JLSemi order codes and a reference circuit.

——— VOOHU Engineering Team

Technical support: fae.thorne@voohu.cn | Tel: +86 400-1048-018

Suzhou VOOHU Electronic Technology Co., Ltd. | www.voohuele.com