Guide: How to use

USB, Thunderbolt, and Power Delivery (updated June 2021)

Charging cables

There are now so many so-called standards for USB, Thunderbolt, and Power Delivery that we have updated our guide – my how it has changed over a year.

USB, Thunderbolt, and Power Delivery Guide cover USB 1.0 to the new Thunderbolt 4 and USB-4. It also covers the confusing power delivery (PD), Extended Power Range (EPR), battery charging (BC) and Quick Charging (QC) standards (and they are not the same things).

In preparing the USB, Thunderbolt and Power Delivery Guide, it was not a matter of looking up a Wiki (wish it were) but consolidating USB standards and battery charging standards. The custodian for USB standards is USB.ORG.

USB, Thunderbolt, and Power Delivery Terms

  • USB-A (and variants like micro-USB,mini-USB etc) – As USB-A should be on the way out now our best advice is to look for USB-C devices.
  • USB-C is a little easier. Well, it was more difficult this time due to the new USB-4 standards. And it seems some manufacturers are pushing the limits of standards as well. For example, USB-C can have a PD from 10W to 100W, but it depends on cable ratings but we will soon see Extended Power Range (EPR) take that to 240W!
  • Thunderbolt 3 (TB3) is much easier – there is only one standard. Intel is the guardian of Thunderbolt and has given it is standard free (without royalty) to the world. Basically, it means all Thunderbolt 3 devices are interoperable.
  • Thunderbolt 4 (TB4) – it is almost the same as TB3 with 40Gbps bandwidth and supports more video bandwidth
  • BC is about charging batteries (mainly USB-A)
  • PD is about using USB-C for intelligent power delivery
  • Fast charge is how fast you can fill the tank (mainly USB-C)
  • Speed 1Mbps = .125MBps = .001Gbps or .000125GBps.
  • Half-duplex (HD) means it can send or receive data but not at the same time (think of a single lane bridge where a car has to stop to let another through)
  • Full-duplex (FD) means it can send and receive data (two lanes) at the same time only losing a small amount of speed.
  • OHMS Law – Volts (V) x Amps (A) = Watts (W) so 5V x 1A = 5W
  • 1000 milliamps per Amp (mA), mAh is the total mA the battery can deliver for one hour.
  • Volts is a linear measure of voltage.
  • Amps are how fast that voltage flows into the battery. Volts generally don’t kill – amps do – 1A can give you a painful shock and 10-20A can kill.
  • Watts are the overall volume or charge ability of V x A.

USB-A only (includes connectors and variants).

  • 1.0 – up to 12Mbps (HD) – black keyed port and up to 5m cable
  • 2.0 – 480Mbps (HD tops out at 280Mbps) – ditto
  • 3.0 – 5Gbps (HD tops out at 3.2Gbps) – blue keyed port and up to 3m cable

USB-C 3.1 or 3.2

  • 3.1 Gen 1 – 5Gbps (FD with the right SuperSpeed cable)
  • 3.1 Gen 2 – 10Gbps (FD with the right SuperSpeed+ cable)
  • 3.2 is just a later version of 3.1 – same speeds
  • 3.2 Gen 2 2×2 – 20Gbps FD

USB-4 (based on Thunderbolt 3)

  • Gen 2×1 – 10Gbps FD with USB-C 3.2, ALT DP1.4a and PCIe tunnelling, Host to host OTG transfers
  • Gen 2×2 – 20Gbps FD – ditto
  • and Gen 3×2 – 40Gbps FD – ditto

Thunderbolt 3

  • Usually, 40Gbps FD over a .5m Thunderbolt certified USB-C cables but older implementations and longer ‘passive’ cables will see that reduce to 10 or 20Gbps.
  • Thunderbolt 2 is 10Gbps FD and 20Gbps HD.

Thunderbolt 4 (TB4) – one port for all (until TB5)

It is basically the same with 1x8K monitor support and unlike TB3 manufacturers must pay Intel a royalty. No prizes for guessing why the royalty-free USB-4 came along so quickly.

Battery charging (BC) Specification (these are not as ‘standard’ as we would like)

BC is for USB-A only and relates to ‘dumb’ chargers. It is unwise o plug a higher rated charger into a lower-rated device as excess power converts into heat. Conversely, you can use a lower-rated charger, and it takes longer to charge.

  • 1.0 is 5V up to 500mAh (2.5W) – there is no intelligence, and the charger should match the device amperage needs, e.g. 5V 300mA (1.5A), 5V/500mA (2.5W).
  • 1.1 is 5V 900mA (4.5W) or 1A (5W)
  • 1.2 is 5V up to 1.5A (7.5W)
  • We have seen a lot of USB-A, 5V/2.4A and 5V/3A (12-15W) chargers and these are outside BC standards – more the PD 1.0 standard below. Do not use these with older USB devices.
  • Generally, USB-A self-powered (bus-powered) devices (using the USB-A 2.0 host or later) draw 5V and from 100mA-1000mA (.5W to 5W).

Obviously, the BC protocol ran out of ‘steam’, and USB-C PD came into play.

Power Delivery (PD) over USB-C

PD means the charger and device have some intelligence (called a power contract or handshake) to deliver the right voltage and amperage. The only catch is that you need a USB-C cable rated for the amperage. You need an EMCA (Electronically Marked Cable Assembly) cable for over 3A. And power can flow upstream (to the device) and downstream (from the device).

PD 1.0 (5V/3A/15W) – smartphones and devices USB devices to 15W:

This is the most common and USB-A to USB-C cables can handle that. If the device does not need the wattage, the charger delivers lower wattage.

You will hear the term ‘fast charge’ bandied around but, it is just pouring (flooding) more wattage into the battery. It is safe, but the jury is out on whether repeated charging shortens battery life.

PD 2.0 used fixed voltages from 5/9/15/20V and 3 to 5A (15-100W).

But it is not an elegant standard relying on large voltage, and amperage jumps from say, 20V/3W for the first 30%, dropping to 15W/3A for the next 20% etc. PD 2.0 tops out at 60W without a special cable.

PD 3.0 is 5V to 20V and 3A to 5A in small increments (15-100W)

It is a more elegant and universal solution because it allows micro-voltage and amperage steps instead of the fixed voltages. In this way, it can deliver higher voltages and lower amperages.

USB On-the-Go (OTG) simply means ports that can send data/power upstream or downstream. USB-C cables are full-duplex; it is the devices that may be half-duplex.

Fast or Quick Charge (QC) for smartphones

There are a few confusing issues like efficiency and loss due to heat but suffice to say that all smartphone batteries are generally 3.3V up to 5000mAh so pouring in 5-20V will not hurt them as long as the amperage is adjusted (watts remain the same).

A 4000mAh battery can deliver 4A for one hour. If your device had a power draw at idle of say 400mA, then it would drain the battery in 10 hours. Similarly, if you want to charge that battery at 10W (5Vx2A) it would take 2 hours to fill but the reality is that lower charging efficiencies make that even longer.

Most, if not all QC technology (except OPPO/vivo/realme) uses flood charging. It floods the battery with the highest volt/amps it will take until about 50% full then steps down to 9V to 75-80% when the standard 5V/2A kicks in. This is to prevent battery fires and help preserve battery life.

Qualcomm Quick Charge

QC requires a compatible Qualcomm SD SoC and a phone that has a QC charging circuit. Standards are backwards compatible.

  • 1.0 – 5V/2A (10W)
  • 2.0 – 5/9/12 (18W) for latter SD2XX/4XX/6XX up to SD810
  • 3.0 – dynamic 200mV increments 3.6-20V up to 18W – SD4XX to SD821
  • 4.0 – dynamic 20mV increments 3.6-20V/2.5-3A (27W) – SD6XX, 710 and 835 and PD 2.0 compatible
  • 4+ – for SD670, 845/855/865/888. PD 3.0 compatible. Introduces Dual charge paths like OPPO VOOC

OPPO (a.k.a. Dash, Dart or Warp Charge and used in vivo and realme

A proprietary solution requires a special dual-channel ‘green’ insert USB-A cable to work with dual batteries; otherwise, it delivers half the amperage. You can use QC compatible chargers, but the maximum is PD 2.0 at 10W.

  • VOOC 2.0: 5V/4A (20W)
  • SuperVOOC: 5V/4A – Find X
  • VOOC 3.0: 5V/5A (25W) for OPPO Reno
  • VOOC 4.0 (not released) is 5V/6A (30W) (also called Warp Charge)
  • Coming 20V/5A (100W)

Samsung Adaptive Fast Charge

Since the Note7 issue, Samsung has been ultra-cautious about battery pedigree (build) and fast charging. In all our tests, Samsung phones maintain the lowest battery temperature, and we think that is best. Note that all chargers support similar Qualcomm QC 2.0 or 3.0 standards as the phones can use Exynos or Qualcomm chips depending on the market.

  • 5/9V and 2A (18W) for its older Galaxy/Note series phones (QC 2.0)
  • 5/9 and 3/2.77A (25W) plus PD 3.3/5.9/3A and 3.3/11/2.25A (28W) for Galaxy 10 5G (QC 3.0)
  • 5/9/12V and 2/1.67/2.1A for its tablets PD 2.0
  • The Note10+ can use a special 10V/4.5A (45W) PD 3.0 charger, but if you use QC 3.0 or 4.0 chargers it only charges at 27W.

GadgetGuy’s take

USB, Thunderbolt and Power Delivery is a whole lot of mumbo jumbo

We put this reference together because we get so many claims about fast charging or USB-C PD that we needed to develop a reference, free from marketing BS. Boy, has a lot changed. One thing has become evident – power is the lifeblood of any device and the ability to recharge it quickly is paramount to users.

Most smartphone fast charge claims are more marketing hype than reality. Most start by claiming, for example, 50% in just 30 minutes, neglecting to tell you that the battery has been flood charged at say 15V/4A (60W) and any longer would risk thermal burnout. A fast charge is a three or even four-stage charge.

Please note that should you find any errors please let me know – there are a lot of numbers here.