LDO Regulator: Basics, Selection, Design & Testing

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1) What is an LDO regulator?

LDO regulator overview with pass element, feedback loop and low headroom — LDO = linear regulator working with very small VIN–VOUT headroom.

Definition (TL;DR)

An LDO regulator—short for Low Dropout (LDO) regulator—is a linear voltage regulator that keeps V_OUT stable when the headroom between V_IN and V_OUT is small. Internally a reference and an error amplifier drive a pass element (PMOS/NPN/NMOS) so that feedback holds the target voltage. Compared with switching regulators, LDOs are quieter and simpler but dissipate heat proportional to (V_IN − V_OUT) × I_LOAD.

Dropout voltage is the minimum V_IN − V_OUT required to stay in regulation at a specified load current. If headroom falls below dropout, the output follows the input (fallout region).

Terminology: Dropout & Headroom

Headroom: H = V_IN,min − V_OUT. Keep H ≥ dropout@I_LOAD.
Pass element: device driven by the error amp (PMOS for very low dropout; NPN/NMOS may need more headroom).
Loop metrics: PSRR vs frequency, output noise, line/load regulation—covered in detail later.

Sources for terminology consistency: Linear regulator / Low-dropout regulator (encyclopedic references).

Traditional vs IC Path

Traditional linear (op-amp + pass / LM317/7805)

Pros: low cost, educational, EMI-benign.
Limits: not inherently low-dropout; protections/stability external; parameter spread.
Use when: large headroom & modest accuracy/noise needs, thermal budget acceptable.

IC LDO regulator (integrated)

Pros: specified dropout@I_LOAD, PSRR/noise plots, protections (OC/TSD), clear C_OUT/ESR window.
Limits: power dissipation rises with headroom × current.
Use when: small headroom, low noise/PSRR targets, compact BOM.

Migration cues: excessive heat, insufficient battery end-of-life headroom, or unmet noise/PSRR → consider an LDO IC or a buck → LDO combo.

LDO vs Standard Linear LDO vs Buck 5-Step Selection

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2) LDO vs Standard Linear Regulators (LM317/7805)

Why this comparison matters

Searching for difference between LDO and normal/standard regulator often stems from assuming “linear = low-dropout”. In reality, low-dropout is defined at the target load current.
Legacy parts like LM317/LM7805 typically need more headroom and can run hot or fall out of regulation at higher currents.
This section gives a one-screen, neutral comparison and prepares you for the 5-step selection workflow.

Pass-element architectures & impact on dropout

“Standard” regulators (e.g., LM317/7805 class) are typically bipolar/Darlington designs and require larger V_IN−V_OUT. Modern LDOs use different pass elements—PMOS, NPN, or NMOS—that trade headroom, PSRR bandwidth, and stability requirements differently.

Architecture	Typical Dropout Trend	PSRR Band	Stability / ESR Window	Notes
Bipolar/Darlington (LM317/7805 class)	Higher; increases with I_LOAD	Good at low-mid freq	Often needs ESR (non-zero) for stability	Robust, inexpensive; not inherently low-dropout
PMOS pass (common LDO)	Very low at light-mid I_LOAD	Good; declines at high freq	Usually stable with ceramic; watch ESR range	Great for small headroom, simple BOM
NMOS/NPN with charge-pump/driver	Low; can sustain at higher I_LOAD	Often stronger at mid-high freq	Ceramic-friendly; check minimum C_OUT	May introduce quiescent-current trade-offs

Dropout vs Load: LM317/7805 vs modern LDO

Read dropout at the current you actually draw. The illustration below contrasts legacy parts with a representative modern LDO at three checkpoints (50/200/500 mA). As load rises, legacy dropout grows faster; a modern LDO keeps regulation with much smaller headroom.

Where legacy still fits

Large headroom and low efficiency sensitivity (bench supplies, educational builds, cost-driven boards).
EMI-critical environments where switching is hard to qualify and heat is manageable.
Be ready to add: external protection (current/thermal), compensated output network with the right ESR, and attention to accuracy/temperature drift.

Thermal reality check

Linear efficiency ≈ V_OUT/V_IN}. Power dissipated: P_d = (V_IN − V_OUT) × I_LOAD. Temperature rise: ΔT ≈ P_d × R_θJA. If ΔT exceeds your budget, move to a buck or a buck → LDO combo.

Quick example (replace with your numbers): VIN=5.0 V, VOUT=3.3 V, ILOAD=0.5 A → Pd=(1.7 V×0.5 A)=0.85 W. With RθJA=50 °C/W → ΔT≈42.5 °C. Check enclosure and ambient limits.

Decision checklist & next steps

Headroom < ~0.3–0.5 V at your load?
Load current ≥ 200–300 mA or spikes that cause large Pd?
Noise/PSRR targets (audio/RF/ADC/PLL) that legacy parts can’t meet?
Need integrated protections, PG/EN, soft-start?
Thermal budget tight or battery EoL margin small?

Go to 5-Step Selection Having heat/dropout issues?

Note: Terminology and definitions in this section align with widely cited references, including Linear regulator and Low-dropout regulator articles on Wikipedia, used here to ensure consistent use of “dropout”, “pass element”, and related concepts.

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3) LDO vs Buck / Switching: When to Use Which

Clarify the concepts

LDO is a linear regulator (analog loop), not a switching DC/DC converter.
Buck / switching regulators use PWM and inductors for high efficiency; LDOs adjust a pass element for low noise and simplicity.
Choice is constraint-driven: noise/PSRR needs, efficiency/thermal budget, EMI compliance, and BOM/size.

Need the math? Jump to Key Parameters & Formulas.

One-page decision tree

Start with two hard thresholds: Noise/PSRR and Efficiency/Thermal. If noise or spur limits are strict (audio/RF/ADC/PLL), prefer LDO or a buck → LDO combo. If power dissipation makes your temperature rise exceed budget, choose a buck, and add an LDO only if a clean rail is still needed.

Decision tree: LDO vs buck vs buck→LDO by noise and heat thresholds — Decision flow: Noise/PSRR → Efficiency/Thermal → LDO / Buck / Buck→LDO.

Noise / PSRR threshold

For audio, RF, PLL, ADC, specify output noise (μV_rms) and PSRR vs frequency at 1 kHz, 100 kHz, and near the buck f_SW.
A single buck rarely meets tight spur/PSRR targets at f_SW. Use buck → LDO with 100–300 mV headroom for ripple cleanup.
Quick budget: V_{OUT,ripple,total} ≈ V_buck,ripple × 10^(−PSRR/20) + V_noise,LDO.

Ripple and spur attenuation by LDO PSRR around the buck switching frequency — Illustrative ripple/spur attenuation with LDO PSRR.

See Applications for audio/RF/ADC notes and post-buck cleanup tips.

Efficiency / Thermal threshold

Linear efficiency ≈ V_OUT/V_IN. Power dissipated: P_d = (V_IN − V_OUT) × I_LOAD. Temperature rise: ΔT ≈ P_d × R_θJA. If ΔT exceeds your budget, use a buck. If you still need low noise, follow with an LDO and keep 100–300 mV headroom.

Quick example (replace with your numbers): VIN=12 V, VOUT=5 V, ILOAD=0.6 A → P_d=(7 V×0.6 A)=4.2 W. With R_θJA=35 °C/W → ΔT≈147 °C (not acceptable) → use a buck; if rail must be quiet, set buck to ~5.2 V and add an LDO to 5.0 V.

Thermal budget visualization comparing LDO dissipation versus buck efficiency — Thermal budget check: when dissipation forces a buck choice.

More formulas in Key Parameters.

The combo: Buck → LDO

Topology: Buck handles large voltage drop efficiently; LDO finishes with the last 100–300 mV for ripple/spur cleanup.
Choose LDO with strong PSRR at the buck’s f_SW and harmonics; verify noise (μV_rms).
Stability with upstream LC: avoid creating an LC at the LDO output; add a small series R/ESR if needed; keep C_IN/C_OUT close.
Layout: short ground returns, star-ground for analog rails, respect the LDO’s C_OUT/ESR window.

Buck followed by LDO topology for ripple cleanup — Post-buck cleanup with an LDO: efficient and quiet.

Edge cases & next steps

Ultra-light load / sleep modes: buck may enter PFM with higher ripple; ultra-low-Iq LDOs can keep analog rails quiet.
EMI & compliance: switching needs filtering/shielding; LDOs are EMI-benign but may run hot.
Cost & BOM: buck adds inductor and switches; LDO keeps BOM minimal.

Go to Key Parameters Go to Applications Go to 5-Step Selection

4) Key Parameters & Quick Formulas

Parameter map & datasheet reading

Core dimensions: Headroom/Dropout, Efficiency/Thermal (η, P_d, ΔT), PSRR & Output noise, Quiescent current (I_q).
Constraint dimensions: Stability (C_OUT/ESR/compensation) and System pins (PG/EN/UVLO/Soft-start).
Datasheet hotspots: Dropout vs I_LOAD curve; PSRR vs frequency; Noise (μV_rms / nV/√Hz); Line/Load regulation & Transient; Stability/ESR window.

Headroom & Dropout

Headroom H = V_IN,min − V_OUT. Dropout is the minimum V_IN − V_OUT required to keep regulation at your specified load current. If H ≥ Dropout@I_LOAD → regulation region; otherwise the output follows the input (fallout). Always read dropout on the curve at your target current and add 20–50% margin across temperature/lot/packaging.

Headroom vs dropout and regulation/fallout regions for an LDO regulator — Geometry of headroom and dropout; regulation vs fallout regions.

Efficiency & Thermal math

Linear efficiency (ignoring I_q): η ≈ V_OUT / V_IN.
Power dissipation: P_d = (V_IN − V_OUT) × I_LOAD.
Temperature rise: ΔT ≈ P_d × R_θJA. Copper pour & thermal pad reduce R_θJA; enclosure and airflow matter.

Quick example (replace with your numbers): V_IN=5.0 V, V_OUT=3.3 V, I_LOAD=0.4 A → P_d=0.68 W. With R_θJA=45 °C/W → ΔT≈30.6 °C. If too high, consider a buck or buck→LDO.

Thermal budget bars showing LDO dissipation and temperature rise — Pd and ΔT relationship for linear regulation.

PSRR vs frequency & output noise

PSRR (dB): suppression of input ripple; typically high at low freq, rolling off with frequency. Check 1 kHz, 100 kHz, and around buck f_SW.
Output noise: specify μV_rms over a bandwidth (e.g., 10 Hz–100 kHz) and/or nV/√Hz density. NR pin can reduce noise with slower startup.
Quick budget: V_OUT,ripple ≈ V_buck,ripple × 10^−PSRR/20 + V_noise,LDO.

PSRR attenuates buck ripple and spurs across frequency for cleaner rails — Ripple/spur attenuation with PSRR and LDO noise floor.

Quiescent current (I_q) & operating modes

I_q dominates battery life in sleep/standby; compare EN=1 vs shutdown, dropout region, and temperature corners.
Some LDOs offer eco modes: lower I_q but often worse PSRR/transient—confirm your trade-offs.
Ground current at light loads can be a large fraction of I_LOAD; read the I_q vs load curve.

Quiescent current versus load and temperature trends — Typical Iq trends vs load and temperature.

Regulation & transient

Line regulation: ΔV_OUT vs ΔV_IN; Load regulation: ΔV_OUT vs ΔI_LOAD.
Load transient: look for overshoot/undershoot and settling time; driven by loop bandwidth & C_OUT/ESR.
For accurate testing, see probe/grounding notes in Testing & Performance Measurement.

LDO transient response to load step; overshoot and recovery — Load-step transient profile: dip/overshoot and recovery.

Stability quick rules (C_OUT & ESR window)

Confirm minimum C_OUT and allowed ESR range; many modern LDOs are ceramic-cap stable but still require certain values.
With an upstream buck, avoid creating an LC at the LDO output; add small series R/ESR if needed.
For layout and full stability guidance, jump to Stability & PCB Layout.

Minimum-stable circuit and ESR window for an LDO regulator — Minimum-stable circuit and ESR window concept.

System pins: PG / EN / UVLO / Soft-start

PG (Power-Good) for sequencing/fault indication; EN for controlled turn-on.
UVLO prevents undervoltage misbehavior; Soft-start reduces inrush and false trips with large C_OUT.
Coordinate with supervisors/reset ICs for robust bring-up of MCU/FPGA/analog rails.

Sequencing with PG, EN, UVLO and soft-start for clean system bring-up — Sequencing with PG/EN/UVLO/Soft-start.

Quick reference table

Parameter	Why it matters	Typical target (scenario)	Common pitfalls	Where to find
Dropout@I_LOAD	Ensures regulation with small headroom	<0.3–0.5 V at target I (battery, post-buck)	Reading at wrong current/temp; zero margin	Dropout vs Load curve
I_q	Sleep/standby battery life	μA→nA (portable/IoT)	I_q rises in dropout or cold corners	I_q vs load/temp
PSRR@1 kHz/100 kHz	Rejects supply ripple/spurs	>60 dB (audio/RF/ADC); high at f_SW	Ignoring high-frequency roll-off	PSRR vs frequency plot
Noise (μV_rms)	Analog fidelity & SNR	Ultra-low for audio/RF/ADC rails	Bandwidth mismatch vs datasheet spec	Noise spec/plot, NR pin
C_OUT & ESR window	Loop stability	Meet minimum C and ESR range	All-ceramic but out-of-range ESR	Stability section
PG/EN/UVLO/SS	Sequencing & reliability	Required for multi-rail systems	False trips, no brown-out margin	Electrical characteristics, timing

Mini worksheet (plug your numbers)

Inputs
V_IN,min=3.6 V
V_OUT=3.3 V
I_LOAD=0.25 A
R_θJA=50 °C/W
[email protected] A=0.20 V
V_buck,ripple=30 mV, PSRR@f_SW=50 dB, V_noise,LDO=10 mV_pp

Headroom & Dropout
H = 3.6 − 3.3 = 0.3 V → H ≥ 0.2 V ⇒ Regulation OK

Efficiency & Thermal
η ≈ 3.3/3.6 = 91.7%
P_d = (0.3 V × 0.25 A) = 0.075 W
ΔT ≈ 0.075 × 50 = 3.8 °C

Ripple/Noise budget
Attenuation = 10^−PSRR/20 = 10^−2.5 ≈ 0.0032
V_OUT,ripple ≈ 30 mV × 0.0032 + 10 mV ≈ 10.1 mV_pp

Go to 5-Step Selection Go to Stability & Layout

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5) How to Choose an LDO (5-Step Workflow)

5-step LDO selection workflow from Vout/Iload to thermal — Workflow: define VOUT & ILOAD → verify dropout headroom → set Iq/PSRR/noise → check stability → confirm thermal/package.

How to use this workflow

Follow 5 steps from needs → headroom → quality (Iq/PSRR/noise) → stability → thermal/package.
If a step fails its threshold, branch to a buck or buck → LDO solution (see Section 3).
Formulas for headroom/efficiency/thermal/noise are summarized in Key Parameters.

Step 1 — Define V_OUT & I_LOAD profile

Specify V_OUT, steady/peak currents, duty cycle, inrush, and V_IN,min at battery end-of-life or cable droop. Compute headroom: H = V_IN,min − V_OUT. This becomes your gating constraint.

Step 1 mini-table (fill):
V_IN,min = ____ V
V_OUT = ____ V
I_static = ____ A
I_peak = ____ A (duty ____%)
Inrush = ____ A / ____ ms

Headroom: H = V_IN,min − V_OUT = ____ V
Tip: consider connector/cable drop and battery ESR under load.

If H ≤ 0.2–0.3 V at meaningful current, prepare for a buck → LDO or a lower-V_OUT target.

Step 2 — Check Dropout @ I_LOAD

Read the Dropout vs Load curve at your target current and add 20–50% margin across temperature/packaging.
Threshold: require H ≥ Dropout@I_LOAD × (1.2–1.5).
If not met: (1) reduce V_OUT, (2) use buck → LDO with 100–300 mV headroom, or (3) pick a lower-dropout LDO.

Record from datasheet:
Dropout@I_LOAD = ____ V
Margin factor = 1.__ → Required H ≥ ____ V

Your headroom: H = ____ V → Pass / Fail

Consider buck → LDO See formulas

Step 3 — Choose I_q / PSRR / Noise

Iq (quiescent current)
Target: ____ μA (sleep) / ____ μA (active)
Note temp corners and dropout behavior.

PSRR vs f
≥ ____ dB @ 1 kHz; ≥ ____ dB @ 100 kHz; high at f_SW= ____ kHz

Output noise
≤ ____ μV_rms (10 Hz–100 kHz); NR pin: Yes/No (start-up trade-off)

For ripple budgeting and PSRR math, see Key Parameters. For scenario tips, see Applications.

Step 4 — Verify stability (C_OUT & ESR / compensation)

Meet the LDO’s minimum C_OUT and allowed ESR range; confirm ceramic-cap stability.
With an upstream buck, avoid forming an LC at the LDO output; add small series R/ESR if required.
Layout preview: keep C_IN/C_OUT within 2–5 mm; short ground loop; route NR/PG/EN away from noise sources.

C_OUT = ____ μF (type: ____); ESR = ____ mΩ (range ____–____ mΩ)

Upstream buck? Yes/No — Series R at LDO OUT: ____ Ω

NR used? Yes/No — PG/EN tied to: ____ — SS time: ____ ms

Stability & Layout details Troubleshooting

Step 5 — Thermal & package

Compute: η≈V_OUT/V_IN, P_d=(V_IN−V_OUT)·I_LOAD, ΔT≈P_d·R_θJA.
Reduce R_θJA with copper pour, thermal pad, vias; consider airflow/enclosure temperature.
If ΔT exceeds budget, use a larger package/heat spreading or move to buck (then buck → LDO if you need a clean rail).

Example box: V_IN=____ V, V_OUT=____ V, I_LOAD=____ A → P_d=____ W; R_θJA=____ °C/W → ΔT≈____ °C → OK/Not OK

Consider buck / buck→LDO See IC Picks by Scenario

Printable checklist

Step	Input / Metric	Target / Threshold	Checked
1 · V_OUT & I_LOAD	V_IN,min, V_OUT, I_static/I_peak	Headroom computed	□
2 · Dropout@I_LOAD	Dropout at target current	H ≥ Dropout × 1.2–1.5	□
3 · I_q / PSRR / Noise	Iq, PSRR@1 kHz/100 kHz/f_SW, μV_rms	Meets scenario targets	□
4 · Stability	C_OUT min & ESR window; buck interaction	Within allowed ranges	□
5 · Thermal & package	η, P_d, ΔT, R_θJA	ΔT within budget	□

Worked example

Given: USB 5 V → 3.3 V, I_LOAD=0.3 A, V_IN,min=4.75 V.
Headroom H=1.45 V (ample).

Step 2: [email protected] A ≈ 0.2 V → Pass (H ≫ 0.2 V).
Step 3: PSRR target high @100 kHz; noise ≤ 10 μV_rms.

Step 4: C_OUT ≥ 10 μF ceramic; ESR within range; upstream buck? No.
Step 5: P_d=(1.7×0.3)=0.51 W; with R_θJA=40 °C/W → ΔT≈20 °C (OK with copper pour).

If ΔT had exceeded budget, switch to a buck and set 3.5 V, then add an LDO to 3.3 V (100–200 mV headroom).

Pitfalls & anti-patterns

Checking only “max current” while ignoring Dropout@target current.
Assuming any ceramic cap works: respect the ESR window.
Measuring noise/PSRR with wrong bandwidth/probing.
Letting light-load I_q dominate battery drain.
Creating an LC with the upstream buck causing ringing/oscillation.

Stability & Layout IC Picks by Scenario Testing methods

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6) Stability & PCB Layout Checklist

Why stability fails

LDOs are analog feedback systems—C_OUT/ESR, load impedance, and trace parasitics set phase margin.
Bad placement (C_IN/C_OUT far away, long ground loop) and upstream buck LC interaction are the top root causes.
Typical fingerprints: low/mid-frequency squeal, excessive ringing on load steps, start-up hiccups, PG not asserting.

Minimum stable circuit

C_IN and C_OUT per datasheet (typical: C_IN ≥ X μF, C_OUT ≥ Y μF).
ESR window: respect the allowed range; inject ESR with a small series R or capacitor choice if needed.
Placement radius: keep C_IN/C_OUT within 2–5 mm of the pins; straight short traces, avoid vias.

Item	Spec / Value	Notes
C_IN	≥ ____ μF (ceramic recommended)	≤ 2–5 mm from VIN–GND pins
C_OUT	≥ ____ μF	Value at DC bias (effective capacitance)
ESR	____–____ mΩ	Inject ESR via series R if all-ceramic is too low
Placement radius	≤ 2–5 mm	Short, wide traces; avoid stubs

Output capacitor & ESR window

Ceramic vs tantalum/aluminum: ceramics have very low ESR (may require added ESR); tantalum/aluminum ESR is higher and varies with temp/freq.
Effective capacitance: X5R/X7R derate under DC bias; verify effective C at your V_OUT.
Paralleling caps reduces ESR further—ensure the net ESR stays within the allowed window.

Input decoupling & placement

Place C_IN right at VIN–GND pins (≤ 2–5 mm) to avoid impedance peaking and extra phase lag.
Keep the ground return short; prefer same-layer routing to avoid crossing split planes.
With large C_OUT, check inrush and upstream source capability during start-up.

Placement/grounding do’s and don’ts for LDO — Good vs bad placement and grounding around an LDO.

Grounding & Kelvin routing

Star / single-point ground: join LDO ground and load ground at a quiet node to prevent load current noise injection.
Kelvin sense: if FB/ADJ is present, sense near the load; route NR/PG/EN away from high dI/dt nodes.
Thermal ground: solid copper under the LDO with thermal pad/vias lowers R_θJA and improves stability margins.

Buck → LDO interaction

Avoid LC at LDO output: C_OUT with upstream buck LC can form a peaking network → ringing/instability.
Damping methods: add a small series R (tens to hundreds of mΩ) at LDO OUT or pick an LDO compensated for upstream LC.
PSRR at f_SW: choose an LDO with strong PSRR near the buck switching frequency and harmonics.

Need the math again? See Key Parameters.

Common mistakes

Ignoring the ESR window or effective capacitance under DC bias.
C_IN/C_OUT placed > 5 mm away; thin, narrow traces; long ground loops.
Routing NR/FB/PG/EN near switching nodes or noisy digital lines.
Paralleling too many ceramics and pushing ESR below the allowed range.
Skipping buck→LDO interaction analysis—leading to unexplained ringing/oscillation.

Symptoms → Causes → Actions

Symptom	Likely causes	Actions
Oscillation / audible squeal	C_OUT/ESR out of range; long leads; upstream LC interaction	Meet ESR window; move caps within 2–5 mm; add small series R; verify stability plot
Large ripple / poor PSRR	LDO PSRR roll-off at f_SW; noisy ground return; insufficient C_IN	Pick LDO with higher PSRR at f_SW; fix grounding; add/relocate C_IN
Thermal shutdown	High (V_IN−V_OUT)×I; poor copper/thermal pad	Increase copper/thermal vias; reduce headroom; move to buck or buck→LDO
Start-up hiccup / PG not high	Inrush too high; NR slows start; UVLO threshold issue	Soft-start; limit inrush; review UVLO/NR; check PG timing
Ringing after load step	Output pole/ESR zero mis-placed; upstream LC coupling	Tune C_OUT/ESR; add small damping R; shorten loop area

Go to Troubleshooting Go to Testing & Measurement

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7) Testing & Performance Measurement

Dropout, PSRR, noise and transient test setups with proper probing for an LDO — Test fixtures for dropout, PSRR, output noise and load transient; use short ground spring probing.

Test principles & equipment

Control variables: warm-up 5–10 min, log ambient/board temp, fix bandwidth/filters, one change at a time.
Gear: low-noise PSU (remote sense), function generator + injection transformer or FRA (PSRR), low-noise preamp (noise), oscilloscope ≥100 MHz (with 20 MHz limit option), electronic load (CC/CR/step), true-RMS DMM.
Accessories: Kelvin/remote-sense leads, coax + 50 Ω term, AC coupling, spring-ground tips, short cables, low-ESR cap kit.
Log sheet: test ID, instruments/SN, probe BW/coupling, cable length, ambient, board notes.

Dropout test

Goal: find the minimum V_IN−V_OUT to hold regulation at target I_LOAD.

Wiring: PSU → (optional 0.1 Ω sense) → LDO; remote/Kelvin sense directly at VIN/GND pins; constant load set to your I_LOAD.
Steps: (1) Fix I_LOAD. (2) Sweep V_IN down in 10–50 mV steps. (3) Record the point where V_OUT deviates >1% → that V_IN−V_OUT is Dropout@I_LOAD.
Pass rule: Headroom H (from design) ≥ Dropout@I_LOAD × (1.2–1.5).
Errors: lead/cable drop, unstable load, no thermal soak, inaccurate current.

See Headroom/Dropout math Troubleshooting

PSRR measurement

Goal: measure suppression of input ripple at key points (1 kHz, 100 kHz, and near buck f_SW).

Method A · Sine injection: Sum a small sine (10–50 mV_pp) onto V_IN using an injection transformer/combiner. Scope V_IN,ripple and V_OUT,ripple with AC coupling, 50 Ω term, spring ground. Compute PSRR(dB)=20·log10(V_IN,ripple/V_OUT,ripple).
Method B · FRA/Bode: Use FRA to sweep frequency; keep load and temperature constant; avoid overdrive into nonlinearity.

Notes: verify oscilloscope bandwidth/filters; log exact amplitude and sweep points; repeat at different I_LOAD.

PSRR formulas & budgets Troubleshooting

Output noise measurement

Goal: measure μV_rms noise over a defined bandwidth (e.g., 10 Hz–100 kHz) and/or nV/√Hz PSD.

Chain: LDO OUT → low-noise preamp (×10/×100) → scope/SA; AC coupling; 50 Ω term; spring ground or coax direct.
Setup: limit scope BW (e.g., 20 MHz) to avoid RF hash; ensure preamp noise floor < DUT; prefer battery/ultra-low-noise PSU.
Readout: integrate in the specified band for μV_rms, or sweep PSD; match datasheet bandwidth.

Noise metrics & NR pin Troubleshooting

Load transient & regulation

Goal: characterize overshoot/undershoot and settling time under current steps; measure line/load regulation.

Wiring: dynamic electronic load (e.g., 10→200 mA, <1 μs edges); probe directly at the output capacitor with spring ground.
Metrics: peak deviation (% of V_OUT), settling to ±1%, ringing/ζ, recovery time; log step amplitude/edge speed.
Line/Load regulation: sweep V_IN/I_LOAD, record ΔV_OUT/ΔV_IN, ΔV_OUT/ΔI_LOAD.

Troubleshooting

Probing & bandwidth hygiene

Prefer spring-ground or coax direct; avoid long alligator grounds.
For time-domain noise and transients, compare with 20 MHz limit vs full BW to avoid aliasing/over-reporting.
Use the same PCB Kelvin sense point for power and measurement to remove lead inductance effects.
Record BW/filters/coupling in your log so others can reproduce.

Pass/Fail thresholds & quick check

Dropout: Dropout@I_LOAD × 1.2–1.5 ≤ Headroom ⇒ Pass; else Fail.
PSRR: meets target dB at 1 kHz / 100 kHz / f_SW (targets set in selection Step 3).
Noise: μV_rms within spec (bandwidth-matched); NR-on start-up time as expected.
Transient: overshoot/settling within limits; no sustained ringing.
Bad-unit hints: abnormal I_q, PG never asserts, V_OUT tracks V_IN (dropout), hot case at low load, oscillation with rated C_OUT/ESR.

Revisit targets Troubleshooting map

Logs & templates + next steps

Test	Conditions	Instrument & settings	Result	Pass/Fail
Dropout	I_LOAD=____ A; sweep VIN ↓	Scope 20 MHz; remote sense	____ V	□/□
PSRR	1 kHz / 100 kHz / f_SW=____ kHz	Sine 10–50 mVpp / FRA sweep	____ dB / ____ dB / ____ dB	□/□
Noise	10 Hz–100 kHz (or ____)	Preamp ×____; 50 Ω; AC	____ μV_rms	□/□
Transient	ΔI=____ mA; edge <____ μs	Probe spring ground; limit BW	Overshoot ____%; settle ____ μs	□/□

Go to Troubleshooting Go to Key Parameters

8) Applications & Design Notes

Battery, audio/RF/PLL/ADC, MCU/FPGA, instrumentation, post-buck cleanup applications for LDOs — Typical LDO applications: battery/portable, audio/RF/PLL/ADC, MCU/FPGA, instrumentation/sensors, post-buck cleanup.

How to read this section

Pick targets by scenario first: Noise/PSRR/accuracy vs efficiency/thermal, then verify Headroom/Dropout@I_LOAD, PSRR@1k/100k/f_SW, Noise (μV_rms), I_q, and ΔT.
Each card below gives a checklist, design notes, a mini example (or calc), and links to deeper sections.
Stuck between topologies? See LDO vs Buck / Buck→LDO. Need formulas? See Key Parameters.

Battery / Portable

Checklist
☐ Ultra-low I_q (sleep μA→nA)
☐ Dropout@active current
☐ Headroom at EoL (V_IN,min)
☐ UVLO/PG set to avoid brown-out

Design notes

Compute H=V_IN,min−V_OUT. If H≲0.2–0.3 V at meaningful current, consider buck→LDO (leave 100–300 mV).
5V LDO regulator from a battery often runs hot; prefer buck for the 5 V rail, keep a small LDO for sensitive analog rails.
3.3 V: check Dropout at peak bursts; 1.8 V: easier thermally but often stricter noise/SNR.

Mini example
1S Li-ion, V_IN,min=3.3 V → 3.3 V/0.2 A ⇒ H=0 V ⇒ must use buck→LDO, set buck ≈3.5 V and LDO 3.3 V.

Headroom & Iq basics When to choose buck→LDO

Audio / RF / PLL / ADC

Targets
☐ Noise ≤ ____ μV_rms (10 Hz–100 kHz)
☐ PSRR ≥ ____ dB @1 kHz; ≥ ____ dB @100 kHz; strong at f_SW=____ kHz
☐ Good line/load regulation

Design notes

Select an LDO with high PSRR near the buck’s f_SW and harmonics; consider using the NR pin (slower start).
Use buck→LDO with 100–300 mV headroom for ripple cleanup; avoid forming LC at the LDO output.
Star ground for analog; route NR/FB/PG away from switching nodes and digital clocks.

Quick calc
V_OUT,ripple ≈ V_buck,ripple × 10^−PSRR/20 + V_noise,LDO
Example: 40 mV × 10^−60/20 + 8 mV ≈ 8.04 mV_pp.

Layout & LC compatibility Noise/PSRR math

MCU / FPGA / DSP

Multi-rail checklist
☐ Core / IO / Analog split
☐ PG/UVLO/EN sequencing
☐ Transient on core rail (FPGA load)

Design notes

High-current core → buck; sensitive analog/reference → LDO.
Use PG/Reset/Sequencer to meet vendor-recommended power-up order.
5V LDO regulator: if V_IN ≫ 5 V, check ΔT; prefer buck then post-LDO if a clean 5 V rail is required.

Mini table
Rail | I_max | Sensitivity | Topology | PG deps
Core | ____ A | Eff | Buck | ____
Analog | ____ A | Noise | LDO | ____
IO | ____ A | Medium | Buck/LDO | ____

5-step selection Stability & layout

Instrumentation / Sensors

Targets
☐ Tight line/load regulation
☐ Low μV_rms / low PSD
☐ Fast recovery to pulsed loads

Design notes

Budget DC accuracy and temperature drift; some rails benefit from a reference-grade LDO.
For bridge/strain/pulsed sensors, verify overshoot and recovery time with a proper transient test.
Use short traces, Kelvin sense near the sensor front-end, and isolate analog ground.

Mini calc
Allowable drift = (Temp range) × (ppm/°C of LDO) × V_OUT → target regulation spec.

Transient testing Accuracy metrics

Post-buck cleanup

Leave 100–300 mV headroom; pick an LDO with strong PSRR at f_SW and harmonics.
Budget: V_OUT,ripple ≈ V_buck,ripple × 10^−PSRR/20 + V_noise,LDO. Reduce ripple, increase PSRR, or add headroom if needed.
Ensure LC compatibility; add a small series R (tens–hundreds mΩ) if LC peaking appears; place C_IN/C_OUT within 2–5 mm.

Topology decision Stability & layout

Scenario quick selector

Scenario	Primary goals	Typical targets	Topology	Notes
Battery wearables	I_q≪100 μA, headroom low	PSRR mid, Noise modest, Dropout low	LDO or buck→LDO	EoL droop + UVLO/PG config
Audio codec / PLL	High PSRR & low Noise	Strong @f_SW, μV_rms low	buck→LDO	Use NR/soft-start; clean layout
MCU/FPGA (multi-rail)	Efficiency + sequencing	Transient OK, PG timing	Buck + LDO for analog	Core buck, analog LDO
Precision sensors	Accuracy & low noise	Noise≪10 μV_rms, tight reg	LDO	Kelvin sense; isolation
5 V rail from battery	Thermal efficiency	ΔT within budget	Buck → LDO (if clean 5 V)	Avoid direct 5V LDO from high VIN

Common pitfalls by application

Battery: checking only max current while ignoring Dropout@active current; missing EoL headroom and UVLO/PG.
Audio/RF: focusing on low-freq PSRR but ignoring f_SW region; routing NR near noisy nodes.
MCU/FPGA: wrong power-up sequence; mixing analog and digital return paths.
Sensors: using nominal capacitance instead of effective value under DC bias; ignoring recovery time to pulsed loads.

Troubleshooting checklist

Reference mini-designs

A · 12 V → buck 5.2 V → LDO 5.0 V (audio/DAC)
Headroom ≈ 200 mV; target PSRR@100 kHz ≥ ____ dB;
C_IN/C_OUT close; ESR window met; small R for damping if needed.

B · 1S Li-ion → buck 2.0 V → LDO 1.8 V (sensor/PLL)
I_q target: ____ μA; Noise ≤ ____ μV_rms;
PG/UVLO/SS sequencing for clean startup; f_SW PSRR verified.

C · USB-C 5 V → LDO 3.3 V (low-current MCU + radio)
ΔT check: P_d = (5−3.3)×I; if hot, buck 3.5 V then LDO 3.3 V;
Verify transient for radio TX bursts.

Where to go next

IC Picks by Scenario Trade-off math & formulas LDO vs Buck decisions

9) IC Picks by Scenario

Scenario buckets for LDO selection across brands — Scenario-centric LDO shortlists across brands: ultra-low Iq, ultra-low-noise/high-PSRR, high-current/very-low-dropout, and AEC-Q100 automotive.

Neutral, scenario-first: We shortlist low dropout (LDO) linear voltage regulators by application metrics, not by brand. Models are ordered by fit to targets; cross-brand near-compatible alternatives are listed where relevant.

Brand pool & how to use

Candidate sources (alphabetical): Texas Instruments, Analog Devices/LTC/Maxim, Microchip, Renesas/Intersil, onsemi, STMicroelectronics, ROHM.

Start from 5-step selection, then match a scenario card below.
Use the comparison matrix at the end to eyeball cross-brand differences (PSRR, noise, I_q, dropout@I).
For stability/layout specifics, jump to Stability & PCB Layout; for formulas, see Key Parameters.

Ultra-low-Iq (coin-cell / IoT)

Slot A · PN: ______ (Brand: ______) Ultra-low Iq

V_OUT range / acc.: ______ V (adj/fixed), ______ %
I_MAX: ______ A | Dropout@I: ______ V @ ______ A
I_q: ______ μA (on), ______ nA (shutdown)
PSRR: ______ dB @1 kHz, ______ dB @100 kHz
Noise: ______ μV_rms (10 Hz–100 kHz)
Stability: C_OUT ≥ ______ μF, ESR ______–______ mΩ
Pkg/Temp: ______ / ______ °C
Datasheet: Link

Near-compatible: ______ (Brand), pinout ______; verify EN/PG/NR.

Submit Your BOM / RFQ Battery/Portable notes

Slot B · PN: ______ (Brand: ______) Ultra-low Iq

V_OUT range / acc.: ______ V, ______ %
I_MAX: ______ A | Dropout@I: ______ V @ ______ A
I_q: ______ μA
PSRR: ______ / ______ dB (1 k/100 k)
Noise: ______ μV_rms (BW: ______)
Stability: C_OUT ≥ ______ μF, ESR window ______–______
Pkg/Temp/AEC: ______ / ______ °C / ______
Datasheet: Link

Near-compatible: ______ (Brand), same DFN2×2 footprint (check pad).

Submit Your BOM / RFQ

Ultra-low-noise / High-PSRR (Audio/RF/PLL/ADC)

Slot C · PN: ______ (Brand: ______) Low-noise · High-PSRR

V_OUT / acc.: ______ V, ______ %
I_MAX: ______ A | Dropout@I: ______ V @ ______ A
I_q: ______ μA | NR: Yes/No
PSRR: ______ dB @1 kHz · ______ dB @100 kHz · ______ dB @ f_SW=____ kHz
Noise: ______ μV_rms (10 Hz–100 kHz)
Stability: C_OUT ≥ ______ μF, ESR ______–______ mΩ
Pkg/Temp: ______ / ______ °C
Datasheet: Link

Near-compatible: ______ (Brand) — check NR/soft-start behavior.

Submit Your BOM / RFQ Audio/RF design notes

Slot D · PN: ______ (Brand: ______) Low-noise · High-PSRR

V_OUT / acc.: ______ V, ______ %
I_MAX: ______ A | Dropout@I: ______ V @ ______ A
I_q: ______ μA
PSRR: ______ / ______ / ______ dB (1 k / 100 k / f_SW)
Noise: ______ μV_rms (BW: ______)
Stability: C_OUT ≥ ______ μF; ESR window ______–______
Pkg/Temp/AEC: ______ / ______ °C / ______
Datasheet: Link

Near-compatible: ______ (Brand), similar WSON/DFN footprint.

Submit Your BOM / RFQ

High-current / Very-low-dropout (hundreds of mA → A-class)

Slot E · PN: ______ (Brand: ______) High-current

V_OUT: ______ V (adj/fixed), acc. ______ %
I_MAX: ______ A | Dropout@I: ______ V @ ______ A
I_q: ______ mA (typ)
PSRR: ______ / ______ dB (1 k / 100 k)
Noise: ______ μV_rms (BW: ______)
Stability: C_OUT ≥ ______ μF (ceramic OK? Y/N), ESR ______–______
Pkg/Temp: ______ / ______ °C; R_θJA ______ °C/W
Datasheet: Link

Near-compatible: ______ (Brand), TO-252/SOT-223 compatible layout (check tab).

Submit Your BOM / RFQ Thermal & ΔT math

Slot F · PN: ______ (Brand: ______) Very-low-dropout

V_OUT / acc.: ______ V, ______ %
I_MAX: ______ A | Dropout@I: ______ V @ ______ A
I_q: ______ mA | Short-circuit/TSD: Yes/No
PSRR: ______ / ______ dB (1 k / 100 k); at f_SW=____ kHz: ______ dB
Noise: ______ μV_rms
Stability: C_OUT ≥ ______ μF; ESR window ______–______
Pkg/Temp/AEC: ______ / ______ °C / ______
Datasheet: Link

Near-compatible: ______ (Brand), same pinout class; verify FB/ADJ/PG nets.

Submit Your BOM / RFQ

AEC-Q100 / Automotive

Slot G · PN: ______ (Brand: ______) AEC-Q100

V_OUT / acc.: ______ V, ______ %
I_MAX: ______ A | Dropout@I: ______ V @ ______ A
I_q: ______ μA · PG/EN/SS: Yes/No
PSRR/Noise: ______ dB @100 kHz · ______ μV_rms
EMC/ESD: ______; Load dump: ______
Stability: C_OUT ≥ ______ μF; ESR window ______–______
Pkg/Temp: ______ / Grade __
Datasheet: Link

Near-compatible: ______ (Brand), pinout ______; check UVLO/PG thresholds.

Submit Your BOM / RFQ Validation tests

Slot H · PN: ______ (Brand: ______) AEC-Q100

V_OUT / acc.: ______ V, ______ %
I_MAX: ______ A | Dropout@I: ______ V @ ______ A
I_q: ______ μA; PSRR ______ dB @100 kHz
Noise: ______ μV_rms (BW: ______)
Stability: C_OUT ≥ ______ μF; ESR window ______–______
Pkg/Temp/AEC: ______ / Grade __ / Q100
Datasheet: Link

Near-compatible: ______ (Brand), similar pinout; verify thermal pad net.

Submit Your BOM / RFQ

Comparison matrix (cross-brand)

Brand	PN	Scenario	V_OUT Range / Acc.	I_MAX	Dropout@I	I_q (modes)	PSRR 1k / 100k / f_SW	Noise μV_rms (BW)	Stability (C_OUT/ESR)	Pkg	Temp/AEC	Notes	Datasheet
______	______	Ultra-low-Iq	______ V / ______ %	______ A	______ V @ ______ A	on: ______ μA; sd: ______ nA	__ / __ / __ dB	______ (____ Hz–____ kHz)	C ≥ ______ μF; ESR ______–______	______	______ / ______	NR? PG? UVLO?	Link
______	______	Low-noise / High-PSRR	______ V / ______ %	______ A	______ V @ ______ A	______ μA	__ / __ / __ dB	______ μV_rms (____)	C ≥ ______ μF; ESR ______–______	______	______ / ______	NR pin; SS time	Link
______	______	High-current / VLD	______ V / ______ %	______ A	______ V @ ______ A	______ mA	__ / __ / __ dB	______ μV_rms (____)	C ≥ ______ μF; ESR ______–______	______	______ / ______	R_θJA ______ °C/W	Link

Notes: Dropout is specified at the stated current/temperature/package. Noise must include bandwidth. PSRR should be read at 1 kHz / 100 kHz / near buck f_SW. I_q varies with mode and dropout. For buck→LDO, keep 100–300 mV headroom.

Next steps & CTAs

Submit Your BOM / RFQ Back to 5-Step Selection Key Parameters & Formulas Stability & PCB Layout Applications & Design Notes

10) Troubleshooting (Symptoms → Causes → Actions)

How to use this page

Match your symptom in the table, then work left→right: confirm the likely causes, apply the actions in order.
If math is needed (Headroom/Dropout/PSRR/Noise), jump to Key Parameters.
If placement/ESR/layout is implicated, go to Stability & PCB Layout; to verify with instruments, see Testing.

Quick triage flow

Rule out measurement artifacts: long alligator grounds, no 50 Ω termination, full-BW noise. If so, fix probing first (Testing).
Headroom check: H = V_IN,min − V_OUT versus Dropout@I_LOAD (need H ≥ 1.2–1.5×Dropout).
CIN/COUT/ESR/layout: values within datasheet window? caps within 2–5 mm? ground loop small?
Upstream buck? Look for LC interaction; consider damping or 100–300 mV post-LDO headroom.
Still failing? Use the Symptoms → Causes → Actions table below.

Fault signatures (scope “fingerprints”)

Oscillation, dropout, thermal shutdown—scope signatures and fixes — Typical waveforms for oscillation (ringing/squeal), dropout (VOUT follows VIN), thermal shutdown (periodic restart), PG jitter on noisy starts.

Symptoms → Causes → Actions

Symptom	Likely causes	Actions
Oscillation / audible squeal	C_OUT/ESR out of stability window; C_IN/C_OUT far; upstream buck LC coupling	Meet ESR window or add small series R (tens–hundreds mΩ); move caps within 2–5 mm; check/damp buck→LDO. Stability/Layout
VOUT below target (worse at load)	Headroom insufficient; Dropout@I_LOAD underestimated; wiring/trace loss	Ensure H ≥ 1.2–1.5×Dropout; pick lower-dropout LDO or use buck→LDO; remote/Kelvin sense; widen traces. Math
Excess ripple / poor PSRR	Low PSRR at f_SW; noisy ground return; insufficient C_IN	Choose LDO with strong PSRR at f_SW; add/relocate C_IN; clean ground; reduce buck ripple or shift f_SW. Verify
Runs hot / thermal shutdown	High (V_IN−V_OUT)×I; high R_θJA; copper/thermal pad insufficient	Recompute ΔT; add copper/thermals; use larger package; switch to buck or buck→LDO topology. Thermal
PG never high / PG jitter; EN odd behavior	UVLO/PG thresholds mismatched; NR/SS slows ramp; excessive startup ripple	Align UVLO/PG thresholds; tune SS/NR; add hysteresis or sequence rails. Layout
Startup hiccup / overshoot	C_OUT/ESR/SS mis-set; LC resonance with upstream	Retune SS/NR; adjust C_OUT/ESR; add small damping R at LDO OUT; review buck compensation. Scope it
Large overshoot / slow recovery on load step	Low phase margin; far probe point; effective C_OUT reduced by DC bias	Increase effective C_OUT; probe at cap with spring ground; set ESR within window; shrink loop area. Transient test
VOUT tracks VIN (poor line regulation)	Operating in dropout; no Kelvin sense at load	Increase headroom; sense at load node; reduce wiring loss. Headroom
Measured noise higher than datasheet	BW/AC coupling incorrect; preamp floor too high; EMI pickup/ground loop	Match bandwidth (e.g., 10 Hz–100 kHz); AC + 50 Ω; use low-noise preamp; shield cables. Noise method
Ringing with upstream buck (series use)	LDO output forms resonant network with buck LC	Add small series R to damp; keep 100–300 mV headroom; pick LDO with strong PSRR near f_SW. Compatibility
Iq abnormally high at light load	Dropout-mode behavior; temperature effects; instrument resolution/offset	Re-test in regulation region; verify meter floor; compare across temperature. Measure Iq
Fails only at hot/cold corners	Temp drift of Dropout/PSRR/ESR; copper/θ_JA worsens	Use temp-corner specs; widen margins; pick parts with better temp stability. Temp effects
Intermittent due to EMI/ESD events	Switching noise coupling; surge sensitivity	Add π filter/ferrite; improve grounding/shield; verify ESD & load-dump ratings (auto). Immunity checks

Measurement hygiene (quick check)

Use spring ground or coax direct; avoid long ground leads; AC-couple when appropriate with 50 Ω termination.
Compare waveforms with 20 MHz limit vs full bandwidth; keep the same Kelvin sense node for power and probing.
Log scope/DMM settings (BW, filters, coupling) for reproducibility. See Testing & Measurement.

When to escalate to design changes

Thermal over budget → move to buck or buck→LDO; lower (V_IN−V_OUT) or current.
Noise/PSRR shortfall → choose a higher-PSRR/low-noise LDO, increase headroom, or reduce upstream ripple.
Chronic headroom issues → adjust system voltages or change topology; revisit 5-step selection and IC picks.

Useful links

Stability & PCB Layout Testing & Measurement Key Parameters & Formulas Applications & Design Notes

11) FAQ (People-Also-Ask)

What is an LDO regulator? How do LDO regulators work?

An LDO (low-dropout) regulator is a linear voltage regulator that maintains a set output with very small input-to-output headroom. Internally it uses a reference, an error amplifier, and a pass element (PMOS/NPN/NMOS) in a feedback loop to keep V_OUT constant under load and line changes. Dropout is defined at a stated load current.

Further reading: What is an LDO · Key parameters

Is an LDO a DC/DC or a switching/buck regulator?

No. An LDO is not a switching converter. It is a linear regulator that dissipates the voltage difference as heat, offering low noise and high PSRR with simple circuitry. A buck is a switching DC/DC that moves energy via an inductor for high efficiency. Many designs use buck → LDO to combine both benefits.

Further reading: LDO vs Buck · Applications

What is dropout voltage and how do I compute headroom?

Dropout is the minimum (V_IN−V_OUT) required to hold regulation at a stated I_LOAD. Compute headroom as H = V_IN,min − V_OUT. Keep H ≥ 1.2–1.5× Dropout@I_LOAD across temperature and package. If H is tight, choose a lower-dropout LDO or a buck → LDO chain.

Further reading: Headroom & dropout math

How do I choose an LDO regulator?

Follow five steps: (1) set V_OUT and the load profile (average/peaks/duty), (2) read dropout vs current, (3) check I_q/PSRR/noise in the needed bands (10 Hz–100 kHz / f_SW), (4) confirm stability (C_OUT, ESR window, NR/comp), (5) verify thermal & package using P_d and θ_JA.

Further reading: 5-step selection · Formulas

When should I use an LDO vs a buck — or buck → LDO?

Use an LDO when rails need low noise/PSRR, simplicity, or small headroom. Use a buck for large VIN−VOUT or high current to limit heat. A buck → LDO chain cleans ripple while keeping efficiency; leave 100–300 mV headroom on the LDO and check PSRR near the buck’s switching frequency.

Further reading: Decision tree · Use-case notes

What are the advantages and disadvantages of LDOs?

Pros: very low noise, high PSRR (audio–mid bands), fast response, small BOM, simple startup, low cost. Cons: efficiency limited to V_OUT/V_IN, heat at high current/headroom, output-cap ESR stability constraints, and lower current than switchers.

Further reading: Trade-offs · Efficiency & thermal

How do I test an LDO (dropout, PSRR, noise, transient)?

Dropout: sweep V_IN down at target I_LOAD, record first >1% V_OUT error. PSRR: sine injection or FRA; measure V_IN,ripple vs V_OUT,ripple. Noise: low-noise preamp and matched bandwidth (e.g., 10 Hz–100 kHz). Transient: step load with fast electronic load and spring-ground probing; compare 20 MHz-limited vs full BW.

12) Further Reading + Submit BOM (48h)

Lead-time → compliance → pin-to-pin → risks (48h) — 48h review deliverables: lead-time, compliance, pin-to-pin/near-drop-in, risks & mitigations, optional sample-kit.

What you’ll get in 48 hours

Lead-time & multi-source: current stock, realistic ETA, second-source options.
Pin-to-pin & near drop-in: package/pinout/function match (EN/PG/NR/ADJ notes), minor deltas called out.
Compliance: AEC-Q100 (if needed), temperature grade, RoHS/REACH statements.
Risk sheet: thermal (ΔT), stability (C_OUT/ESR), PSRR/noise vs f_SW, upstream LC compatibility, lifecycle risk.
Sample-kit (optional): device shortlist + EVB tips to validate quickly.

Submit your BOM / RFQ

Required fields

Target V_OUT, load profile (avg/peak/duty), VIN range & headroom budget
PSRR targets @ 1 kHz / 100 kHz / f_SW, noise (μV_rms) window
Stability constraints: C_OUT value/technology, ESR limits, board space/package
Environment: temperature range, AEC-Q100 need, preferred/acceptable brands

Helpful attachments

Schematic + PCB snapshot of the LDO area (CIN/COUT placement)
Current LDO PN; upstream buck PN & f_SW
Measured issues (if any): oscillation, heating, PG/UVLO, transient

SLA: 48h on business days. If clarification is needed, we will reach out first.

Submit Your BOM / RFQ See IC picks 5-step selection

Our review flow

Lead-time: stock, ETA, lifecycle (Active/NRND/EOL), alternates.
Compliance: AEC-Q100 grade, temperature class, RoHS/REACH statements.
Pin-to-pin: package & pinout map, function alignment (EN/PG/NR/ADJ), threshold/polarity deltas.
Risks: ΔT (P_d×θ_JA), stability (C_OUT/ESR), PSRR@f_SW, LC interaction, supply continuity.

Thermal & headroom math Stability/layout SOP Troubleshooting map

Neutrality & privacy

Brand-neutral: recommendations ranked by scenario metrics, not vendor preference; cross-brand pin-compatible options listed where applicable.
Privacy: your BOM is used only for engineering assessment and sourcing checks; NDA can be arranged upon request.
Disclaimer: proposals require system-level validation (thermal, EMC, reliability) in your environment.