LDO Regulator Selection: What Designers Need to Know

A Low-Dropout Regulator (LDO) turns a higher input voltage into a clean, low-noise rail for analog and RF circuits. Choosing the wrong LDO can waste battery life, cause noise or fail when the input sags. This guide covers the key parameters.

1. What is an LDO

An LDO is a linear regulator that works even when the input is only slightly above the output. It is simple, quiet and requires few external components — ideal for post-regulation after a switching buck or for analog/RF rails.

2. Dropout voltage

Dropout is the minimum input-to-output difference the regulator needs to stay in regulation. A "100 mV LDO" works when VIN is only 100 mV above VOUT. Lower dropout means you can run the rail closer to the input and use a lower-cost input supply.

Type	Dropout	Typical use
Standard	1–2 V	Post-buck, simple
Low dropout	100–300 mV	Battery, low headroom
Ultralow	50–100 mV	Single-cell, near-dropout

3. Quiescent current (Iq)

Iq is the current the LDO itself consumes. For battery-powered devices, a low Iq (1–30 µA) extends battery life. For always-on circuits, choose an LDO with low shutdown current.

4. PSRR and noise

• PSRR (Power Supply Rejection Ratio) — how well the LDO rejects ripple on the input. Higher is better (e.g. 60 dB at 1 kHz).
• Output noise — low noise (µVrms) is important for ADCs, PLLs, RF and audio.

5. How to choose

• Confirm VIN max and VOUT + dropout ≤ VIN.
• Choose Iq based on your battery budget.
• High PSRR / low noise for analog and RF rails.
• Check thermal: power dissipation = (VIN − VOUT) × ILOAD.

We stock LDO regulators in SOT-23 / SOT-89 / DFN packages, 2.2–30 V input, 1.2–5 V output. Send us your rail and current needs — we'll recommend the right part.

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