100nF
Embedded and hardware engineering notes, measurements, and tools.
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Latest posts
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How a flyback converter works: stored energy and the clamp
Energy goes into the transformer's gap while the switch is on and out through the secondary when it turns off. CCM against DCM, and the leakage clamp.
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NTC thermistors: the B value, and why reading one heats it
An NTC loses 2–6 % of its resistance per kelvin, and two numbers describe it: R25 and B. What B is, the tolerance butterfly, and self-heating.
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PCB stackups: what each layer is for, 2 to 8 layers
A stackup is a set of promises about where return currents flow. TI's 6, 8 and 10-layer stacks, Microchip's 2 and 4-layer ones, and why each layer order works.
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What a LiPo charger does: constant current, then voltage
A Li-ion charger is a current source that becomes a voltage source: 1C to 4.2 V, then 4.2 V held until the current falls to 0.1C, with a precharge below 2.5 V.
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Ethernet magnetics: what the transformer and centre tap do
The transformer between a PHY and its RJ-45 gives 1500 V of isolation and common-mode rejection; the centre-tap resistors are Bob Smith termination.
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Current sense resistors: what makes a shunt different
A shunt is chosen for the 10–130 mV it drops, and fails for reasons the value hides: TCR once I²R heats it, and the solder a two-terminal connection adds.
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MOSFET gate drivers: from an MCU pin to a half-bridge
Why a microcontroller pin is a poor gate driver, and how an N-channel high side is driven: bootstrap, charge pump, half-bridge IC or transformer.
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ADC and DAC basics: what the datasheet numbers mean
An ADC turns a voltage into one of 2ⁿ codes; the datasheet says how far the part sits from that staircase. LSB, static errors, SNR and Nyquist, per TI SLAA013.
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What an IC's thermal pad is for, and how to solder it
The exposed pad on a QFN or PowerPAD is the die pad and the heat path out of the package, but only once it is soldered. Why the stencil prints 50–70 % of it.
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Where to put a bypass capacitor: mounting, distance, BGAs
The vias and traces a bypass capacitor connects through add as much inductance as the part, 0.4 to 4 nH for one 0402 per XAPP623, and set where it resonates.
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Why an op amp oscillates with a capacitive load
A capacitor on the output makes a pole with the op amp's output impedance and eats phase margin: 100 Ω, 1 MHz and 10 nF leave 22.5°. SBOA418 fixes it.
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What a ground loop is, what causes it, and how to break it
A ground loop is two grounds joined by more than one path. 200 mV per inch of shared wire on a logic edge, hum on a scope trace, a split plane as an antenna.
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How ESD protection works: why layout is half of the diode
An 8 kV discharge is 150 pF through 330 Ω: 30 A in under a nanosecond. A TVS turns that into 10 V; TI's layout guide shows every nanohenry adds 40 V.
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Crystal, oscillator or ceramic resonator: which clock?
A crystal is ±120 ppm over ten years, a ceramic resonator ±1.1 %, an RC oscillator ±2 %, and each is right for something. What UART, USB and a radio need.
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Oscilloscope probes: 10:1, and why the ground lead rings
A probe is a circuit, not a wire: 10 MΩ and 11 pF, a 117 nH ground lead, and a bandwidth of its own. An 11 pF probe on a 6-inch clip rings at 140 MHz.
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Level shifters: one MOSFET per line, or a translator IC
A 3.3 V device and a 5 V device can share a line safely. For open-drain buses one MOSFET per line does it, with no direction pin: AN10441's circuit.
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SPI vs I2C: which is faster, and why the answer is both
SPI is faster because nothing caps its clock and it spends 8 clocks per byte; I2C spends 9 and stops at 3.4 Mbit/s. Four reasons the choice is not about speed.
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Pull-up vs pull-down resistors: which one, and what value
Which direction, and what value: top set by leakage and bottom by the driver's sink current, 1.8 kΩ to 727 kΩ in TI's case, which is why 10 kΩ works.
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Dropout voltage: why the datasheet number is not yours
Dropout is a resistance times your load, not a figure: TI's 160 mV at 200 mA is 0.8 Ω, so 100 mA drops 80 mV. Where it comes from, and how to check headroom.
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Switch debounce: the RC, the Schmitt trigger and the numbers
A switch bounces up to 10 ms; logic answers in nanoseconds. Würth's RC and a Schmitt input fix it, but the 1 µF crosses the SN74HC14's threshold mid-bounce.