LM317LMX/NOPB — 100mA Adjustable Voltage Regulator (SOIC-8)

What Are the Technical Specifications of the LM317LMX/NOPB?

Key numbers that matter. Per the TI LM317L-N datasheet (SNVS775, Rev L), all electrical specs are tested at a 625mW dissipation ceiling. That ceiling, not the 100mA rating, is the real constraint in an SOIC-8 with 160°C/W. At a 40V input-output differential, keep the load under about 15mA.

And it needs a load. The part's own quiescent current flows out through the VOUT pin, so with no real load the output creeps up. Budget 5mA minimum of load current, or design the divider to draw it.

When Should You Use (and NOT Use) the LM317LMX/NOPB?

What Are the Alternatives to the LM317LMX/NOPB?

LM317LMX/NOPB vs LM317LDR2G — the sourcing decision. Both are 100mA LM317L-class parts in SOIC-8, so the choice usually comes down to which manufacturer your BOM is already qualified for. Keeping both approved costs nothing at design time and saves you a line-down situation when one of them goes on allocation.

But if the load is anywhere near 100mA, step up to the LM317G-AA3-R or LM317T. Running a 100mA regulator at 95mA continuous with a 160°C/W package leaves no thermal margin for the bad days.

What Are the Typical Applications of the LM317LMX/NOPB?

Op-amp bias and analog rails. A ±15V audio or instrumentation front-end needs a quiet, adjustable supply. The LM317L's 0.003% output noise and 65dB ripple rejection — 80dB with a 10µF ADJ capacitor — beat a buck converter's switching artifacts by 30dB for a few cents of BOM cost.

LED string drivers. In constant-current mode, one resistor sets the string current: I = 1.25V / R. A 20mA indicator string uses 62Ω. Five LEDs at 3V forward drop fit comfortably inside the 37V output ceiling, and the current limit stays flat across temperature.

NiMH and lead-acid trickle chargers. The same current-source trick makes a 50mA NiMH trickle charger with a 25Ω resistor. Simple, inherently current-limited, and safe to leave connected — the part's own thermal and safe-area protection does the supervision.

Adjustable bench references. A trimmer on R2 gives a lab-grade adjustable supply from 1.2V to 37V in a square centimetre. Add the protection diodes (input-to-output, ADJ-to-output) when the output exceeds 25V or the ADJ cap exceeds 10µF, and it survives bench abuse.

Why Buy LM317LMX/NOPB from ICMASS?

The whole LM317 family in one shipment. LM317LMX/NOPB (SOIC-8, 100mA), LM317LDR2G (onsemi second source), LM317T (TO-220, 1.5A) and LM317G-AA3-R (SOT-223, 1A) all ship from one Shenzhen warehouse. One order, one invoice, one set of customs paperwork.

Date-code traceability on a heavily remarked part. The LM317 family is one of the most remarked devices in gray-market channels. We trace every reel back to the TI or onsemi factory lot. Ask us for date codes before you buy — that question alone filters most questionable sources.

Cross-reference support that respects your layout. If the SOIC-8 pinout doesn't suit a redesign, we'll walk the alternatives with you — LM317G-AA3-R, AMS1117-ADJ, or a fixed LDO — with pinout and thermal numbers, not sales talk.

Frequently Asked Questions About the LM317LMX/NOPB

Q1: Is the LM317L the same as an LM317?

A: No — the LM317L is the 100mA version, the LM317 is 1.5A. Same 1.25V reference and two-resistor topology, but the LM317LMX/NOPB limits at 200mA typ and carries 1/15th the current rating. Per the TI LM317L-N datasheet (SNVS775), I_MAX is 100mA. A circuit that ran happily on an LM317T will starve on an LM317L if it ever needs more than 100mA.

Q2: Why does my LM317L output voltage rise with no load?

A: The minimum load current is 5mA max (3.5mA typ) — below that, the output floats up. The LM317L's quiescent current returns to the output pin, so with nothing loading the rail the output cap charges past the set point. Size R1/R2 to draw at least 5mA, or add a small permanent load like an LED.

Q3: My LM317L oscillates with a small ceramic on the output. Why?

A: Capacitances between 500pF and 5000pF on the output cause ringing — go smaller or much bigger. The LM317L is stable with no output cap, and stable with 1µF tantalum or 25µF aluminum electrolytic, which swamp the marginal zone. A bare 1nF–4.7nF ceramic lands right in the unstable window.

Q4: Can the LM317L work as a microamp current source?

A: No — below roughly 1mA it drifts and misbehaves. Community tests trying 50µA regulation (e.g. on All About Circuits) measured slow, unstable output. The LM317L's adjust-pin current of up to 100µA is itself comparable to the target current. Use a precision current source or op-amp-based circuit below 1mA.

Q5: How much input-output voltage difference does the LM317L need?

A: Design for at least 2.5V of headroom, 3V for rated specs. Dropout is about 1.8V typ, and the datasheet's regulation specs are tested with V_IN − V_OUT = 5V. TI engineers on E2E characterize the part for a minimum 2.5V differential. It is not an LDO — tight-rail designs should use AMS1117-class parts.

Q6: Do I need protection diodes on an LM317L circuit?

A: Only above 25V output, or with an ADJ capacitor over 10µF at outputs above 6V. An input-to-output diode protects against input shorts discharging large output caps; an ADJ-to-output diode protects the reference when the ADJ cap discharges backward. Below those thresholds the internal 50Ω path and 2A-capable output junction handle it.

Q7: How do I get the best ripple rejection from the LM317L?

A: Add 10µF from ADJ to ground — rejection improves to 80dB typ at 120Hz. Without it you get 65dB typ. Above 120Hz the improvement fades, so for switching-frequency ripple keep the input bypass close and consider a ferrite bead upstream.

Q8: Can the LM317LMX replace an LM317T on my existing board?

A: Not directly — different package, different pinout, 1/15th the current. The LM317T is a TO-220 with 1.5A rating; the LM317LMX is an SOIC-8 with four VOUT pins and 100mA. If you need surface-mount with real current, the LM317G-AA3-R (SOT-223, 1A) is the drop-in direction, not the LM317L.

Q9: What should I do with pins 5 and 8 (NC)?

A: Leave them unconnected — or tie them to the VOUT pour for extra copper. Pins 5 and 8 are no-connects with no internal bond. If your layout joins them to the output copper anyway, you get a free thermal path and slightly better heat spreading.

Q10: Why is my output voltage a few hundred millivolts higher than calculated?

A: The adjust-pin current flows through R2 and adds an error term. The formula is V_OUT = 1.25V(1 + R2/R1) + I_ADJ × R2, and I_ADJ is 50µA typ, 100µA max. With R2 = 5.1kΩ, that's up to 0.51V of error. Smaller divider values reduce it — at the cost of more standing current.