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SOT-223 · AMS1117-1.8
Active1A LDO Regulator (1.8V)
AMS1117-1.8
Advanced Monolithic Systems · SOT-223 · 1A LDO Regulator (1.8V)
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Overview
The AMS1117-1.8 is the fixed 1.8 V member of Advanced Monolithic Systems' 1117 low-dropout family, a PNP pass-transistor regulator rated at 1 A that is pin- and function-compatible with TI's LM1117 and Linear Technology's LT1117 in the same SOT-223 outline. Output is trimmed to about ±1% at 25 °C by a Zener-trimmed bandgap, dropout is 1.1 V typical at 800 mA and roughly 1.15 V to 1.3 V at the full 1 A, and the device will hold regulation with an input as low as about 3.2 V. Line regulation is 0.2% maximum and load regulation 0.4% maximum across the family, so for a 1.8 V rail the total static error budget is well inside 2% for most digital and analogue loads.
Protection is the reason the 1117 family survived: on-chip current limiting around 1.2 A to 1.5 A and thermal shutdown near 150 °C junction, plus a pass device whose safe operating area is internally compensated. Stability requires a minimum 10 µF output capacitor — tantalum historically, and 22 µF X5R ceramic today — placed close to the output pin, because the loop compensation relies on the capacitor's ESR and bulk; without it the regulator can oscillate under fast load steps. Input bypass of 10 µF is recommended whenever the supply is more than about 150 mm away or comes from a long cable.
The parameter that most often surprises buyers is ground-pin current: 5 mA typical and 10 mA maximum, and it does not fall at light load. In a battery product drawing 50 µA in sleep, an AMS1117 alone will drain the cell in weeks, which is why low-Iq alternatives such as the HT7533 (4 µA), MCP1700 (1.6 µA) or ME6211 exist. SOT-223 thermal performance is the other constraint: junction-to-ambient is about 60 °C/W on a modest pad, so a 1 A load with 3.3 V in and 1.8 V out dissipates 1.5 W and produces roughly a 90 °C rise — acceptable only with a large copper pour on the tab, and impossible above about 600 mA without it. Always derate: compute (VIN - VOUT) x IOUT plus VIN x IGND against your ambient and the 125 °C junction limit.
Commercially, the AMS1117 is one of the most-produced LDOs in Asia, and Advanced Monolithic Systems, Diodes Incorporated (AZ1117), UMW and several Korean and Chinese fabs all make pin-compatible parts. That depth keeps price low (typically a few cents in reel quantities) but makes counterfeit and remarking common: relabelled lower-current die, 3.3 V parts remarked as 1.8 V, and re-tinned pulls are all seen in broker stock. Verify with a variable load that the output holds 1.8 V at 1 A without thermal foldback, measure ground current (a genuine part draws 5 mA to 10 mA; clones often 15 mA or more), and check laser-etched marking with consistent font and date code. MOQ from our Shenzhen warehouse is 100 pcs loose or 2,500 pcs on tape-and-reel, shipping in one to two business days.
Key Features
- Fixed 1.8 V output at up to 1 A from a 3.2 V to 15 V input
- 1.1 V typical dropout at 800 mA — works from a 3.3 V rail
- Pin-compatible SOT-223 second source for LM1117 and LT1117
- On-chip current limiting and thermal shutdown near 150 °C junction
- 0.2% line and 0.4% load regulation with a 10 µF output capacitor
Typical Applications
- 1.8 V core and I/O rails for FPGAs, MCUs, sensors and codec chips
- Post-regulation from a 3.3 V or 5 V system rail on dense digital boards
- DDR, PLL and VCO bias supplies needing a quiet linear rail
- Networking, set-top box and telecom line-card auxiliary supplies
- Prototyping and small-batch builds where an SOT-223 pad is easier than a TO-220
Specifications
- Output Voltage
- 1.8 V
- Input Voltage
- 3.2 to 15 V
- Output Current (Max)
- 1 A
- Dropout Voltage (Typ, IOUT = 800 mA)
- 1.1 V
- Quiescent Current (Max)
- 10 mA
- Line Regulation (Max)
- 0.2 %
- Load Regulation (Max)
- 0.4 %
- Output Capacitor (Min for Stability)
- 10 µF
- Pins
- 3
- RoHS
- Compliant
Procurement Tips
Add the output capacitor (22 µF X5R 0805 minimum) to the same BOM line as the regulator and state the pad copper area on the assembly drawing — the two most common AMS1117 field failures are oscillation from a missing bulk capacitor and thermal shutdown from an un-poured SOT-223 tab.
Frequently Asked Questions
AMS1117-1.8 versus LM1117-1.8 — are they interchangeable?
Electrically they are the same family with the same SOT-223 pinout (pin 1 ground, pin 2 output, pin 3 input, tab output) and both supply about 1 A with a 1.1 V to 1.2 V dropout. TI's LM1117 is guaranteed to 800 mA with tighter documentation, a 0 °C to 125 °C range and a broader package selection; AMS1117 is cheaper and rated 1 A but with looser test limits. For a cost-sensitive consumer board either works; for automotive or medical, specify the TI or onsemi part with the temperature grade you need.
Can I run the AMS1117-1.8 from a 3.3 V rail?
Yes, and that is its most common use. Dropout is 1.1 V typical at 800 mA and about 1.2 V at 1 A, so a 3.3 V input leaves margin down to roughly 2.9 V to 3.0 V before regulation is lost. Remember that USB and lithium rails sag: a 3.3 V rail from a buck converter under transient load may dip to 3.1 V, which is fine, but a discharged cell plus diode drop will not be. If your input can fall below 3 V, choose a true low-dropout part such as the MCP1700-180 or ME6211C18 with a dropout under 200 mV.
Why is my AMS1117 output unstable or ringing on load steps?
Almost always the output capacitor. The 1117 family needs at least 10 µF of low-ESR capacitance at the output; a 100 nF ceramic alone is not enough and will oscillate. Use 22 µF X5R or X7R ceramic (derated for DC bias) or a 10 µF to 22 µF tantalum, placed within a few millimetres, with the feedback ground returning to that capacitor. Note that very low-ESR ceramics below about 10 µF can also be unstable because the loop expects some ESR zero — adding a 0.5 Ω to 1 Ω series resistor restores the pole position if needed.
How much current can I draw in a SOT-223 package before it overheats?
Do the arithmetic rather than trusting the 1 A rating. With about 60 °C/W junction-to-ambient on a modest pad, 25 °C ambient and a 125 °C junction limit you have a 100 °C budget, or about 1.6 W. A 3.3 V to 1.8 V conversion allows roughly 1 A (1.5 W plus ground current), but 5 V to 1.8 V allows only about 450 mA. On a large pour with vias the figure improves by 30% to 50%. Above about 600 mA on a small pad, move to a buck converter or a DFN/TO-252 package with a real thermal plane.
Is the AMS1117 a good choice for battery-powered products?
Rarely. Ground-pin current is 5 mA typical and 10 mA maximum at all loads, which is 1,000 times worse than an HT7533 (4 µA) or MCP1700 (1.6 µA). In a device that spends most of its life asleep, that quiescent draw will dominate runtime. Keep the AMS1117 for mains-powered or always-on rails where cost and 1 A capability matter, and use a micropower LDO for battery sleep paths.
How do I identify a counterfeit AMS1117-1.8?
The 1117 family is one of the most-remarked regulator families in the market. Check laser-etched marking with the correct font and a plausible date code — ink that wipes off with acetone is a reject. Then test: load to 1 A and confirm the output stays within 1.8 V ±2% while the case temperature rise matches your thermal calculation; measure ground current (5 mA to 10 mA genuine, often 15 mA or more on clones); and verify dropout by lowering the input until regulation breaks, which should happen near 2.9 V to 3.0 V at 800 mA. Clones remarked from a 3.3 V part will read 3.3 V on the output and fail instantly, but remarked low-current die passes a light-load test and folds back under load.
What is the MOQ and lead time?
MOQ is 100 pcs loose for prototypes or 2,500 pcs on tape-and-reel for volume. Shenzhen stock ships in one to two business days; factory channel replenishment for Advanced Monolithic Systems parts is four to eight weeks, and Diodes Incorporated AZ1117 equivalents are available from authorised distribution in similar time frames.
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