Answer: The adjustable AMS1117 in SOT-223 holds 1.25 V between OUT and ADJ, needs VIN − VOUT ≥ 1.3 V at 0.8 A and at least 10 mA of load (worst case), and dissipates into a 90 °C/W package. AMS orders it as plain “AMS1117”; “-ADJ” is distributor naming. In practice, current is limited by heat, not by the 1 A rating. (AMS1117 datasheet pp.1–5.)
Key specifications
| Parameter | Value | Condition | Source |
|---|---|---|---|
| Output current (rated) | 1 A | Dropout is specified only up to 0.8 A | p.1 Features; p.3 Note 4 |
| Reference voltage VREF | 1.232 / 1.250 / 1.268 V | IOUT = 10 mA, TJ = 25 °C | p.2 Electrical Characteristics |
| VREF, full range | 1.2125 – 1.2875 V | 1.5 V ≤ VIN − VOUT ≤ 12 V, full temperature range (bold row) | p.2 Electrical Characteristics |
| Dropout voltage | 1.1 typ / 1.3 max V | IOUT = 0.8 A, ΔVREF = 1 % | p.3 Electrical Characteristics, Note 4 |
| Minimum load current | 5 typ / 10 max mA | VIN − VOUT = 1.5 V | p.3 Electrical Characteristics, Note 5 |
| Adjust pin current IADJ | 55 typ (25 °C) / 120 max µA (full range) | IOUT = 10 mA, 1.5 V ≤ VIN − VOUT ≤ 12 V | p.3 Electrical Characteristics |
| Line regulation | 0.015 typ / 0.2 max % (0.035 / 0.2 % full range) | 1.5 V ≤ VIN − VOUT ≤ 12 V | p.2 Electrical Characteristics |
| Load regulation | 0.1 typ / 0.3 max % (0.2 / 0.4 % full range) | VIN − VOUT = 1.5 V, 10 mA ≤ IOUT ≤ 0.8 A | p.2 Electrical Characteristics, Notes 2–3 |
| Ripple rejection | 60 min / 75 typ dB | 120 Hz, COUT 22 µF tantalum, CADJ 10 µF, IOUT 1 A, VIN − VOUT 3 V | p.3 Electrical Characteristics |
| Input voltage (abs. max) | 15 V | — | p.2 Absolute Maximum Ratings |
| Junction temperature range | −40 to 125 °C | Control section and power transistor | p.1 Ordering Information; p.2 Absolute Maximum Ratings |
| θJA, SOT-223 | 90 °C/W | Soldered; 46 °C/W to > 90 °C/W depending on copper | p.2 Absolute Maximum Ratings (footnote) |
| θJC (all packages) | 15 °C/W | — | p.3 Electrical Characteristics |
| Thermal shutdown | 165 °C | Junction, at the sense point | p.4 Application Hints |
| Output capacitor | 22 µF solid tantalum | Covers all cases, including a bypassed ADJ pin | p.4 Application Hints – Stability |
Pinout (SOT-223)
| Pin | Function | Source |
|---|---|---|
| 1 | Ground / Adjust (ADJ on this part) | p.1 Pin Connections |
| 2 | VOUT | p.1 |
| 3 | VIN | p.1 |
AMS gives one 3-pin list for the fixed and adjustable versions. On the adjustable part, pin 1 goes to the R1/R2 divider, not to ground.
Design notes
Setting VOUT. AMS gives VOUT = VREF × (1 + R2/R1) + IADJ × R2 (p.4, Figure 2). The datasheet expects the divider current to cover the 10 mA minimum load, so R1 = 1.25 V / 10 mA = 125 Ω is the ceiling; AMS shows R1 values of 100–200 Ω in its ripple discussion (p.5), but only the low end of that range meets 10 mA on its own. Use the AMS1117-ADJ calculator for resistor pairs.
Ripple and the ADJ capacitor. Without a capacitor on ADJ, output ripple scales with VOUT / VREF (p.5), so a 5 V output passes about 4× the ripple a 1.25 V output would. To bypass ADJ, the capacitor’s impedance at the ripple frequency must be below R1. AMS’s own numbers: with R1 = 100 Ω, more than 13 µF at 120 Hz, or 0.16 µF at 10 kHz (p.5). Once ADJ is bypassed, keep the 22 µF tantalum on the output (p.4).
Load regulation wiring. Connect the top of R1 directly to the regulator’s output pin and the bottom of R2 to the load’s ground (p.4–5, Figure 3). If R1 sits at the load end instead, the trace resistance is multiplied by (R1 + R2)/R1. For example, with a 5 V divider of R1 = 120 Ω and R2 = 360 Ω, that factor is 4: a 20 mΩ trace behaves like 80 mΩ, which is 40 mV of extra droop at 0.5 A instead of 10 mV.
Heat sets the real current limit. PD = (VIN − VOUT) × IOUT and TJ = TA + PD × θJA must stay ≤ 125 °C (p.5). From 12 V to 5 V at TA = 40 °C with the 90 °C/W figure, the budget is (125 − 40)/90 = 0.94 W, or about 135 mA. AMS’s copper table (p.5, Table 1: 1/16” FR-4, 1 oz) shows 55–80 °C/W with a 2500 mm² back-side plane. At 55 °C/W the same case allows about 220 mA. Line and load regulation are only guaranteed up to 1.2 W in SOT-223 (p.3, Note 2).
Protection diode. None is needed between ADJ and OUT. An output-to-input diode is recommended only when there is a crowbar on the input and the output capacitance is large, in the 1000–5000 µF range (p.4).
Pitfalls specific to AMS1117-ADJ
- Searching AMS’s table for “-ADJ”. It isn’t there. The AMS ordering table lists the adjustable parts as AMS1117 (SOT-223), AMS1117CD (TO-252) and AMS1117CS (SO-8) (p.1). “AMS1117-ADJ” is a catalogue name, so check which maker a listing actually ships.
- Grounding pin 1 out of habit. With ADJ tied to ground, R2 = 0 and the output sits at about 1.25 V.
- R1 = 240 Ω copied from LM317 designs. That divider draws 5.2 mA, below the 10 mA worst-case minimum load, so with no load the output can drift high.
- Counting on 1.3 V dropout above 0.8 A. Note 4 says dropout rises above 0.8 A, and no limit is given there.
- Assuming any capacitor is stable. AMS guarantees stability with 22 µF solid tantalum (p.4) and gives no ESR window. An MLCC-only output is untested territory: check it on the bench. If you need a stated ESR range, compare equivalents.
Part numbers (information only)
| AMS code | Package | Output | Page |
|---|---|---|---|
| AMS1117 | SOT-223 | Adjustable | This page |
| AMS1117CD | TO-252 (DPAK) | Adjustable | AMS1117CD |
| AMS1117CS | SO-8 | Adjustable | AMS1117CS |
| AMS1117-3.3 | SOT-223 | 3.3 V fixed | AMS1117-3.3 |
| AMS1117-5.0 | SOT-223 | 5.0 V fixed | AMS1117-5.0 |
All are listed for −40 to 125 °C junction temperature (p.1). AMS lists no tape-and-reel suffixes.
FAQ
- Is “AMS1117-ADJ” an official AMS part number? No. The AMS ordering table (p.1) calls the adjustable SOT-223 part simply AMS1117; the TO-252 and SO-8 versions are AMS1117CD and AMS1117CS.
- What is the largest R1 I can use? About 125 Ω, if the divider must carry the 10 mA worst-case minimum load (p.3). Larger R1 needs a real load that never drops below 10 mA.
- How much current can a SOT-223 AMS1117 deliver from 12 V to 5 V? Heat limits it to roughly 135 mA at 40 °C ambient with the 90 °C/W rating, or about 220 mA with a good copper plane (55 °C/W from the p.5 table).
- Do I need a capacitor on ADJ? Only if you want better ripple rejection. Size it so its impedance at the ripple frequency is below R1, for example more than 13 µF at 120 Hz with R1 = 100 Ω (p.5), and keep 22 µF tantalum on the output.
- Does the AMS1117 need protection diodes? Not normally. AMS recommends an output-to-input diode only with an input crowbar and very large output capacitors (p.4).
Related (internal links)
- AMS1117-ADJ resistor calculator
- AMS1117 equivalents (LM1117, LD1117, CJT1117B)
- AMS1117CD (TO-252)
- AMS1117CS (SO-8)
- AMS1117-3.3
- Voltage divider calculator
- Linear voltage regulators
- SMD package sizes
Sources (retrieved 2026-10-26)
- Advanced Monolithic Systems, AMS1117 1A Low Dropout Voltage Regulator (DS1117; no revision code printed): http://www.advanced-monolithic.com/pdf/ds1117.pdf (page numbers are PDF page order). Checked against a mirror copy of this PDF (sha256 189a2651…a3f0); AMS prints no revision code, so we cannot prove it is the newest issue.
Disclaimer
Values are copied from the AMS1117 datasheet listed above, read on 26 Oct 2026; the worked numbers are our arithmetic on those values. Thermal results depend on your board. Verify against the current datasheet and measure your design before production.
Reviewed by: Jasper · Updated: 2026-10-26