UMW AMS1117 Complete Selection Guide

Chip Positioning and Core Value

Interpretation of Core Electrical Parameters

• Input/Output Voltage: Provides fixed versions (1.2V/1.5V/1.8V/2.5V/3.3V/5.0V) and adjustable versions. The maximum input voltage is usually 15V-18V; it is recommended to reserve 20% margin during design to prevent surges. The AMS1117 pinout is closely related to voltage output, and the corresponding pin definition can be found in the AMS1117 datasheet.
• Maximum Output Current: Rated continuous current is 1A. Note that this is the guaranteed value within the full temperature range; derating use according to thermal resistance is required in high-temperature environments.
• Dropout Voltage: Typical value is 1.2V@1A. This means that if the output is 3.3V, the input must be at least 4.5V to maintain voltage regulation; strict calculation is required in low input voltage scenarios.
• Output Precision: The precision of the fixed version is ±2%, and the precision of the adjustable version is as high as ±1.5%, which is better than the industry general standard, suitable for digital loads sensitive to voltage.
• Operating Temperature: Full industrial grade range of -40℃ to +125℃, ensuring long-term stable operation in harsh environments.
• Package Type: Mainstream packages include SOT-223 and TO-252 (DPAK); package selection is directly related to heat dissipation capacity and current-carrying upper limit. The AMS1117 pinout varies slightly with the package, which needs to be confirmed in the AMS1117 datasheet.

Voltage Suffix, Package and Temperature Grade Selection

• Voltage Suffix:
• UMW AMS1117-3.3: Fixed 3.3V output, no external voltage divider resistor required, simplifying design and reducing BOM quantity.
• UMW AMS1117-ADJ: Adjustable output version, which can set any voltage (1.25V-13.8V) through two external resistors, with high flexibility but occupying PCB area.

• SOT-223: Suitable for applications with limited space and current <800mA, such as handheld devices or low-power modules.
• TO-252 (DPAK): With a large-area heat dissipation pad on the back, it must be soldered to the PCB copper foil, suitable for 1A full load or high-temperature environments, and its heat dissipation performance is significantly better than SOT-223. If overheating occurs during use, you can refer to our special article 《UMW AMS1117 Overheating Severely?》 for solutions.

Typical Application Circuit Description

1. Input Capacitor: It is recommended to place a 10µF tantalum capacitor or 22µF electrolytic capacitor near the pin to suppress input transient fluctuations. The connection position should be consistent with the AMS1117 pinout shown in the datasheet.
2. Output Capacitor: Must use a tantalum capacitor above 22µF or a low ESR electrolytic capacitor. Official data emphasizes that the high ESR of ordinary aluminum electrolytic capacitors may cause loop instability or even oscillation.
3. PCB Layout: For TO-252 package, the bottom heat dissipation pad must be connected to a large-area ground plane through a via array to reduce thermal resistance and prevent overheating shutdown.

Common Pitfalls in Selection and Practical Use

• Pitfall 1: Mismatched Output Capacitor ESR
• Symptoms: Large power output ripple, even low-frequency self-oscillation, leading to system reset.
• Solutions: Strictly select tantalum capacitors. If ceramic capacitors must be used due to cost, a 0.5Ω~1Ω resistor should be connected in series at the output to simulate the ESR characteristics of tantalum capacitors.

• Symptoms: When the input voltage is slightly low, the output voltage drops with the input, and the system cannot work normally.
• Solutions: Keep in mind the typical dropout voltage of 1.2V. For example, when the output is 3.3V, the input will enter the non-voltage regulation area when it is lower than 4.5V, and the front-end power margin needs to be checked.

• Symptoms: The chip temperature rises rapidly to 125℃ under full load, triggering thermal protection and cutting off the output. For more solutions to overheating problems, you can refer to 《UMW AMS1117 Overheating Severely?》.
• Solutions: Calculate power consumption $$P=(V_{in}-V_{out}) \times I_{out}$$. If the dropout voltage is large (such as 12V to 3.3V), it is strictly forbidden to use LDO, and DC-DC converter should be used instead.

Pin to Pin Alternative Solutions

• Compatibility: It can directly replace classic models such as TI LM1117-3.3 and LM1117-ADJ without modifying the PCB layout or peripheral circuits. The AMS1117 pinout is completely consistent with the LM1117, ensuring seamless replacement.
• Advantages: On the premise of maintaining the same or even better output precision (1.5% for adjustable version), it significantly reduces material costs, and the delivery cycle is more stable, making it the preferred solution for localization replacement.