Words the notes use

Alt mode

Alternate mode, on USB-C

A way for a USB-C port to carry something besides USB, such as DisplayPort video, mostly on its fast pairs and sideband pins. No pin changes job until both ends agree on the mode in messages on CC.

Often confused with

USB4. USB4 also runs on all four fast pairs as one link, like Thunderbolt 3. The host enters it with a Power Delivery message of its own, Enter_USB, where an alt mode needs Enter Mode.

In notes

Note 14, PHY and link layer · Note 23, USB-C alt modes

Antipad

The ring of bare board cleared around a via or pin where it passes through a plane it must not touch.

Often confused with

Thermal relief. An antipad keeps a pin off the plane. A relief joins them through spokes.

In notes

Note 1, Ground cut

Body diode

Its reverse recovery charge, Qrr, in nC

A diode built into every silicon MOSFET, from source to drain, that carries current backwards through the switch while it’s off. Conducting fills it with charge, and the other switch has to pull that charge out at full voltage, its reverse recovery.

Often confused with

Output capacitance. Both are charge the turning-on switch has to pull out. Every switch holds output charge, GaN too. Only a diode that has conducted holds recovery charge.

In notes

Note 4, Gate ringing · Note 10, Zero-voltage switching · Note 11, GaN vs silicon · Note 20, FET choice

Buck converter

A switching converter that makes a lower voltage from a higher one, chopping its input with switches and smoothing it through an inductor and capacitor. Its output sits near its input times its duty cycle.

V_out≈dV_in

Often confused with

Buck-boost. A buck-boost can make its output above or below its input. Note 22’s SIMO runs its 3.3 V rail in buck-boost, so it holds as the cell runs down below 3.3 V.

In notes

Note 6, Spread spectrum · Note 10, Zero-voltage switching · Note 12, Power inductors · Note 22, SIMO converters

CC pins

Configuration channel: CC1 and CC2

Two USB-C pins, CC1 and CC2, that tell a port which way a plug went in and carry the messages that agree on a mode. The plug’s one CC wire meets only one of them, and a device normally pulls it down through Rd, 5.1 kΩ.

Often confused with

SBU pins. The SBU pins, A8 and B8, sit on the other side of the USB 2 pins from CC. They carry nothing in plain USB, while the CC pins say which mode a port is in.

In notes

Note 23, USB-C alt modes

CC-CV charging

Constant current, then constant voltage

Charging at a constant current until the cell reaches its full voltage, then holding that voltage while the current tapers off. The charge stops once the current falls to a set fraction, a tenth in Note 15 and a twentieth in Note 18.

Often confused with

Balance charge. A balance charge runs the same CC-CV on the whole pack and also watches every cell. A plain CC-CV charge sees only the pack's total.

In notes

Note 15, Battery balance · Note 18, LiPo vs LiFePO4 · Note 21, Power quadrants

Cell balancing

Evening out the charge in each cell of a series pack, so every cell ends a charge at its full voltage. A balancer reads each cell through the balance lead and bleeds or moves charge from the one that leads.

Often confused with

Active balancing. Most balancers are passive and bleed the leading cell's extra charge through a resistor as heat. Active balancing moves that charge into the other cells instead.

In notes

Note 13, Capacitors · Note 15, Battery balance · Note 18, LiPo vs LiFePO4

Characteristic impedance

Z₀, in Ω

The impedance an edge sees as it runs along a line, set by the trace's width, its height over the plane and the board between them. USB 3 pairs are built to 90 Ω, HDMI and DisplayPort pairs to 100 Ω.

Z₀ = LC

Often confused with

Resistance. An ohmmeter reads almost nothing along a 90 Ω trace. The 90 Ω comes from the trace's inductance and capacitance, and only a fast edge sees it.

In notes

Note 1, Ground cut · Note 8, Eye diagram · Note 16, TDR

Coulomb counting

Tracking a battery's charge by adding up the current that flows in and out of it, read through a shunt. Any offset in the current reading adds up too, so the count needs a fixed point to reset it, such as a full charge.

q=∫Idt

Often confused with

Voltage gauge. A voltage gauge reads charge from a rested cell's voltage. On a LiPo it comes close. On a LiFe, 10 mV off fits anything from 42 to 71%.

In notes

Note 18, LiPo vs LiFePO4

Current-sense amplifier

An amplifier made to read the few millivolts across a shunt and scale them up for an ADC. Its inputs sit wherever the shunt sits: near ground below the bottom FET, at the supply above the top one.

Often confused with

Current-sense resistor. The resistor, or shunt, carries the current and drops a few millivolts. The amp only reads that drop, through two sense lines.

In notes

Note 5, Shunt taps · Note 9, Chip journeys · Note 19, Sense position

dBµV

Decibels above one microvolt, the unit EMI receivers read in. 0 dBµV is 1 µV, 60 dBµV is 1 mV and 120 dBµV is 1 V.

dBµV=20 log₁₀(V/ 1 µV)

Often confused with

dBm. dBm is power above one milliwatt. Into 50 Ω, 0 dBm is 107 dBµV.

In notes

Note 6, Spread spectrum

DC bias

Of a ceramic capacitor

The fall in a ceramic capacitor’s capacitance as the DC voltage across it rises. Its ceramic adds capacitance by turning its dipoles to line up, and once most have turned, each extra volt stores less.

Often confused with

X5R and X7R. Codes like X5R and X7R say how capacitance moves with temperature. They say nothing about voltage, and DC bias comes on top.

In notes

Note 13, Capacitors · Note 22, SIMO converters

Dead time

The short gap in a half bridge when both switches are off, so one has let go before the other turns on. The current keeps flowing meanwhile, through a body diode or the switches’ capacitance.

Often confused with

Turn-on delay. A turn-on delay is the FET’s own wait after its gate command before any current flows, 886 ns for Note 20’s IRFS7530 at 60 mA. Dead time is the gap a driver leaves between two gate commands.

In notes

Note 4, Gate ringing · Note 10, Zero-voltage switching · Note 11, GaN vs silicon · Note 19, Sense position · Note 20, FET choice

Duty cycle

A share of each cycle, in %

The share of each switching cycle that a switch spends on. In a half bridge it is the share of time the switch node sits at the supply.

d=t_onT

Often confused with

PWM frequency. Frequency is how many cycles run each second, 30 kHz on moteus-c1. Duty is how much of each one the switch is on, and either can change without the other.

In notes

Note 19, Sense position · Note 22, SIMO converters

EMC

Electromagnetic compatibility

A device's ability to work among other electronics: it keeps its own noise under the limits and survives the noise and zaps around it.

Often confused with

EMI. EMI is the noise itself. EMC is passing both ways.

In notes

Note 2, USB-C shell · Note 6, Spread spectrum

ESD

Electrostatic discharge, tested in kV to IEC 61000-4-2

A spark from a charged person or object into a device. The current peaks in under a nanosecond.

Often confused with

Surge. A surge, tested to IEC 61000-4-5, lasts tens of microseconds and carries far more energy.

In notes

Note 1, Ground cut · Note 2, USB-C shell

Eye diagram

A fast signal cut into slices two bits wide and stacked on top of each other. The opening in the middle is the link's margin: its height in volts, its width in time.

Often confused with

Eye mask. The eye is the signal itself. A mask is the keep-out a spec draws inside it, and every sample that lands in the mask is a hit.

In notes

Note 8, Eye diagram · Note 17, Via stubs

GaN FET

Gallium nitride transistor

A power transistor made of gallium nitride instead of silicon. GaN holds its voltage across about a tenth of the distance, so a switch of the same resistance is a smaller chip, with less charge on its gate and drain.

Often confused with

Silicon carbide. Silicon carbide is the other material replacing silicon in power switches. SiC FETs are built like silicon ones, body diode included, and serve mostly higher voltages and powers.

In notes

Note 11, GaN vs silicon

Gate charge

Qg, in nC

The charge a driver has to push into a FET’s gate to turn it fully on. At a set gate current, a gate that holds more charge takes longer to fill, and the FET spends longer half on.

t_g=Q_gI_g

Often confused with

Input capacitance. Input capacitance, Ciss, is the gate’s capacitance at one voltage, 13.0 nF for Note 20’s IRFS7530. Gate charge also counts the flat stretch, where the gate waits for the drain.

In notes

Note 11, GaN vs silicon · Note 20, FET choice

Half bridge

Two switches stacked across a supply. The point between them, the switch node, swings from ground to the supply each cycle.

Often confused with

Full bridge. A full bridge is two half bridges, with the load between their switch nodes.

In notes

Note 4, Gate ringing · Note 19, Sense position · Note 20, FET choice

Jitter

In ps, or in UI, a share of one bit

Edges arriving a little early or late against where they belong. Random jitter has no limit, so the more bits you watch, the wider the crossings of an eye get.

Often confused with

Noise. Noise moves the signal up and down and thickens the rails. Jitter moves the edges early or late and widens the crossings.

In notes

Note 8, Eye diagram

Kelvin connection

Four-terminal sense

Sense lines that leave a resistor at its body, apart from the current path, so they read the resistor and none of the copper.

Often confused with

Two-wire sense. Taps on the current path read the copper's drop too. On Note 5's 0.5 mΩ shunt, taps 2 mm out read 41% high.

In notes

Note 5, Shunt taps

LDO

Low-dropout regulator

A linear regulator that needs only a small margin, its dropout, between input and output to hold its output steady. It drops the whole difference across itself and turns it into heat.

P_heat=(V_in−V_out)·I_out

Often confused with

Quiescent current. Quiescent current is what an LDO draws to run itself, 25 nA for Note 22’s TPS7A02. Its real loss there is the 2.6 V it drops at 40 mA, 104 mW.

In notes

Note 22, SIMO converters

Lead time

How long a maker or distributor expects a new order of a part to take to arrive. It includes waiting for a factory slot as well as making and shipping.

Often confused with

Cycle time. Cycle time is how long a part takes to make and ship. Most of the L298N's 52 weeks is waiting for a slot, not making.

In notes

Note 9, Chip journeys

LiFePO4

Lithium iron phosphate, also LiFe or LFP

A lithium-ion cell with a lithium iron phosphate cathode, full at 3.60 V and averaging 3.3 V. Its voltage barely moves through most of its charge, so voltage says little about how full it is.

Often confused with

LiPo. A LiPo has a lithium cobalt oxide cathode, full at 4.20 V and averaging 3.7 V. Hobby packs of both look alike, but a LiFe's label says LiFe and 3.3 V a cell.

In notes

Note 6, Spread spectrum · Note 15, Battery balance · Note 18, LiPo vs LiFePO4

Line code

8b/10b, 128b/132b, Manchester and more

The rule that turns bits into the levels a wire carries. Codes like 8b/10b also add bits, so the line stays balanced and full of edges for the receiver's clock.

Often confused with

Error correction. Error correction such as Reed-Solomon or LDPC adds bits so the far end can repair errors. A line code adds bits to keep the line balanced and full of edges.

In notes

Note 14, PHY and link layer · Note 23, USB-C alt modes

Low-side sensing

Measuring current with a shunt between the bottom FET and ground, so the amp's inputs sit near ground. In a half bridge the shunt carries the motor's current only while the bottom FET is on.

Often confused with

High-side and in-line sensing. A high-side shunt sits between the supply and the top FET, and an in-line one in the motor's lead. Both need an amp whose inputs ride 48 V.

In notes

Note 19, Sense position

Matching network

A few inductors and capacitors between a radio and its antenna that turn the antenna's impedance into 50 Ω, so less power reflects.

Often confused with

Radiation efficiency. A match only stops reflection. On 10 mm of ground a perfect match lifts 22% to 43%. The rest heats the board.

In notes

Note 3, Antenna ground

Mutual inductance

M, in nH

How much of one circuit’s magnetic field another circuit’s loop catches, per amp. A changing current in the first puts a voltage on the second.

V=MdIdt

Often confused with

Self-inductance. Self-inductance, the 4.7 µH printed on an inductor, links a part’s changing current to the voltage across itself. Mutual inductance links it to the voltage on another circuit.

In notes

Note 12, Power inductors

On-resistance

Rds(on), in mΩ

The resistance between a FET’s drain and source while its gate holds it fully on. The current through it heats it by I²R, and the resistance rises as the FET warms.

P=I²R

Often confused with

ESR. ESR is the resistance inside a capacitor, always in series with it. On-resistance belongs to a switch, and only while its gate holds it on.

In notes

Note 11, GaN vs silicon · Note 20, FET choice

Open-circuit voltage

OCV, in V

A cell's voltage with no current flowing, once it has settled. It follows the cell's charge, so a gauge can read charge from it where the curve is steep.

Often confused with

Voltage under load. Under load a cell reads below its open-circuit voltage, by its current times its resistance, and above it while charging. TI's gauge waits 30 minutes by default before it trusts the voltage.

In notes

Note 15, Battery balance · Note 18, LiPo vs LiFePO4

Output capacitance

Coss, in pF. Its charge, Qoss, in nC

The capacitance between a FET’s drain and source, charged whenever voltage builds across the switch. It is largest near zero volts and falls as the voltage rises, so Note 10 counts its charge instead.

Q_oss=∫V0C_ossdV

Often confused with

Eoss. Eoss is the energy the capacitance stores, 0.65 µJ for Note 10’s two switches at 48 V. Moving their charge costs ½QV, 0.80 µJ, whatever the curve.

In notes

Note 4, Gate ringing · Note 10, Zero-voltage switching · Note 11, GaN vs silicon

PHY

Physical layer, layer 1

The part of a link that decides how bits look on the wire: the voltages, the line code and where the clock comes from. On Ethernet it is often a chip of its own, between the processor and the jack.

Often confused with

MAC. The MAC is the link layer. It builds frames, addresses them and checks them. The PHY under it turns their bits into signals on the wire.

In notes

Note 14, PHY and link layer

Quadrant

On the voltage-current plane, numbered 1 to 4

One of the four parts of the voltage-current plane, set by the signs of a supply’s output voltage and current. Note 21 puts voltage along the bottom and counts counterclockwise from the top right, so quadrants 1 and 3 source and 2 and 4 sink.

Often confused with

Keysight’s numbering. Keysight’s guides put voltage up the side, so their quadrant 2 is Note 21’s quadrant 4, a sink at positive voltage. Source and sink mean the same in both.

In notes

Note 21, Power quadrants

Quasi-peak

QP, read in dBµV

An EMI receiver's detector that charges fast and leaks away slowly. Below 30 MHz it charges in 1 ms and leaks over 160 ms, so a signal that repeats often reads near its peak.

Often confused with

Peak and average. For the same signal, peak reads highest, then quasi-peak, then average. Note 6 reads all three.

In notes

Note 6, Spread spectrum

Radiation efficiency

The share of the power an antenna accepts that leaves as radio waves. The rest heats the copper and the board.

η = P_radP_acc

Often confused with

Total efficiency. Total efficiency counts the reflected power too. Note 3's 22% is total, its 43% is radiation efficiency.

In notes

Note 3, Antenna ground

Read window

The time the bottom FET must stay on in each PWM cycle so a low-side shunt can be read after its amp settles. moteus-c1 needs 3 µs of each 30 kHz cycle, which caps phase duty at 91%.

d_max=1 −t_wT

Often confused with

Settling time. Settling time is how long moteus gives the amp after the bottom FET is told on, 1.5 µs at a gain of 20. It reads in the middle of the window, so the window is twice that.

In notes

Note 19, Sense position

Reflection

Reflection coefficient ρ, from −1 to +1

The part of a signal sent back where a line's impedance changes. Its share is the reflection coefficient, from −1 at a short through 0 on a match to +1 at an open end.

ρ = Z − Z₀Z + Z₀

Often confused with

Return loss. Return loss is the same reflection in dB, counted as a loss. A reflection coefficient of 0.1 is 20 dB of return loss.

In notes

Note 1, Ground cut · Note 3, Antenna ground · Note 8, Eye diagram · Note 16, TDR · Note 17, Via stubs

Regenerative supply

A supply that sinks through switching stages and returns the power it takes to the grid, instead of turning it into heat.

Often confused with

Regenerative braking. Regenerative braking is a motor turning its motion back into current, as Note 21’s braking motor does. A regenerative supply can take that current and pass the power on to the grid.

In notes

Note 21, Power quadrants

Ringing

A decaying swing after a fast edge, set by the loop's stray inductance and the FET's capacitance.

f = 12π√(LC)

Often confused with

Overshoot. Overshoot is the first peak past where the edge settles. Ringing is the whole swing that follows.

In notes

Note 4, Gate ringing · Note 11, GaN vs silicon · Note 19, Sense position · Note 20, FET choice

Rise time

Timed 20 to 80% or 10 to 90%, in ps or ns

The time an edge takes to climb from a low share of its step to a high one, usually 20 to 80% or 10 to 90%. On a smooth edge, 10 to 90% is 1.52 times 20 to 80%.

Often confused with

Slew rate. Slew rate is how steep the edge is, in V/ns. Rise time is how long it takes, so a bigger step in the same rise time slews faster.

In notes

Note 1, Ground cut · Note 4, Gate ringing · Note 8, Eye diagram · Note 16, TDR · Note 19, Sense position

S21

Insertion loss, in dB

How much of a sine at each frequency gets through a part, from its first port to its second, in dB. 0 dB is all of it, and the more negative, the less gets through.

S21 = 20 log₁₀(V₂/V₁)

Often confused with

Reflection. S21 is what gets through to the far end. Reflection, S11, is what comes back toward the source.

In notes

Note 17, Via stubs

SBU pins

Sideband use: SBU1 and SBU2

Two USB-C pins, SBU1 and SBU2, that carry nothing in plain USB and are free for an alt mode or accessory to use. DisplayPort moves its AUX channel there, and an audio adapter its microphone.

Often confused with

Sideband channel. The sideband channel is one signal on the SBU pins, the one Thunderbolt 3 and USB4 run there: SBTX on SBU1 and SBRX on SBU2 in USB4. Other modes put other signals there, such as DisplayPort’s AUX.

In notes

Note 23, USB-C alt modes

SIMO converter

Single-inductor multiple-output converter

A switching converter that feeds several rails from one inductor, filling it and emptying it into one rail at a time. Each rail asks for a packet when it sags, and the rails take turns.

Often confused with

One buck and LDOs. One buck followed by LDOs also gets by with one inductor, but each LDO burns its drop as heat. A SIMO switches every rail.

In notes

Note 22, SIMO converters

Sink

Of a supply, as against source

A supply sinks when it takes power back from its load instead of giving it. Its voltage and the current out of its + terminal then have opposite signs, so their product is negative.

P=VI

Often confused with

Sink device. In HDMI, as in Note 14, the sink is the device at the receiving end of a link, such as a display. A supply sinks when power flows back into it.

In notes

Note 21, Power quadrants

SMU

Source-measure unit

A 4-quadrant supply with a precision meter built in, so it can set a voltage and read the current, or set a current and read the voltage. Keithley calls its SMUs SourceMeters.

Often confused with

Bench supply. A bench supply shows its voltage and current too, but it only sources, in quadrant 1. An SMU reaches all four quadrants and reads them with a precision meter, which is part of its price.

In notes

Note 21, Power quadrants

Spread spectrum

Δf, in kHz

Moving a converter's switching frequency in a pattern, so its noise spreads across a band instead of piling up at one frequency.

Often confused with

Frequency hopping. Frequency hopping moves a radio's carrier between channels. A converter spreads its own noise to lower the peaks.

In notes

Note 6, Spread spectrum

Supercapacitor

Supercap, in farads

A capacitor that stores charge as ions packed against porous carbon, with no insulating layer. The carbon’s huge surface lets a small can hold a whole farad, at only a few volts.

Often confused with

Lithium-ion capacitor. A lithium-ion capacitor is half supercap, half battery. Note 13’s runs 1 mW for 40 h against the supercap’s 52 min, but must never go below 2.2 V.

In notes

Note 13, Capacitors

SuperSpeed pair

TX1, RX1, TX2 and RX2

One of the four fast pairs of pins in a USB-C receptacle, TX1, RX1, TX2 and RX2, that carry USB 3 or an alt mode’s fast signals. Plain USB 3 uses one TX and one RX pair, picked by which way the plug went in.

Often confused with

Lane. A USB 3 lane is two pairs, one TX and one RX. A DisplayPort lane is one pair, so DisplayPort on 2 lanes takes TX2 and RX2.

In notes

Note 1, Ground cut · Note 23, USB-C alt modes

TDR

Time-domain reflectometry

A step source and a fast scope on one line, which read the line's impedance from the echoes of a step. Each echo's delay says where the impedance changes, and its size says by how much.

x = t2τ

Often confused with

VNA. A VNA measures the same reflections one frequency at a time. One inverse FFT turns them into a TDR trace.

In notes

Note 16, TDR · Note 17, Via stubs

Thermal relief

Spokes that join a pin to a plane across a ring of bare board, so the plane can't pull away a soldering iron's heat.

Often confused with

Antipad. An antipad keeps a pin off the plane. A relief joins them through spokes.

In notes

Note 7, Thermal relief

Utilization

Of a SIMO’s inductor, in %

The share of time a SIMO’s inductor spends filling and emptying packets, counted over every rail. At 100% the packets run back to back, and any more load makes the rails droop.

U=t_busyt

Often confused with

Duty cycle. A duty cycle is one switch’s share of a fixed period. A SIMO has no fixed period, and its busy time counts every packet to every rail.

In notes

Note 22, SIMO converters

VDM

Vendor-defined message, named by its SVID

A USB Power Delivery message on the CC wire that carries a 16-bit ID, its SVID, naming the standard or company it belongs to. Structured VDMs are how a host asks who the other end is and which modes it knows, then enters one.

Often confused with

Unstructured VDM. An unstructured VDM sits outside the Discover and Enter steps. A Switch 2 and Nintendo’s dock trade more than 30 vendor messages before video.

In notes

Note 23, USB-C alt modes

Via stub

The leftover length of a via's plated barrel below the layer the signal leaves on. It hangs off the line like a short wire with an open end, and notches the signal where it is a quarter wave long.

f_notch = c4Lε_r

Often confused with

Trace stub. A trace stub is a branch of trace off the line, like the lead to a test pad. It rings the same way, but you can route it away. A via stub comes with the hole.

In notes

Note 8, Eye diagram · Note 16, TDR · Note 17, Via stubs

Zero-voltage switching

ZVS

Turning a switch on only after a current has already pulled the voltage across it to zero. With nothing across it, there is almost nothing to turn into heat.

I≥Qt_dead

Often confused with

Valley switching. Valley switching waits for the lowest point of the ring, which isn’t zero. Note 11’s silicon flyback still turns on at 78 V and dumps its drain’s charge.

In notes

Note 10, Zero-voltage switching · Note 11, GaN vs silicon