ACM7805
Ultra-low-noise 500mA LDO with 8μVrms noise, 80dB PSRR, and wide input range for precision analog applications.
Product Overview
Description
The ACM7805 is a high-performance low-dropout linear regulator designed for noise-sensitive analog and RF applications.
With ultra-low output noise of 8μVrms and excellent PSRR of 80dB at 1kHz, this LDO provides clean power for precision ADCs, DACs, and RF circuits.
The device operates from 2.5V to 16V input and delivers up to 500mA output current with only 200mV dropout voltage at full load.
Product Series
ACM
Primary Application
ADC/DAC power supply
Key Features
- Ultra-low output noise: 8μVrms
- High PSRR: 80dB at 1kHz
- Wide input voltage range: 2.5V to 16V
- Low dropout voltage: 200mV at 500mA
- Excellent load/line regulation
- Current limit protection
- Thermal shutdown protection
- Enable pin for power management
Specifications
| Input Voltage | 2.5V to 16V |
|---|---|
| Output Voltage | 5V (fixed) |
| Output Current | 500mA |
| Dropout Voltage | 200mV @ 500mA |
| Output Noise | 8μVrms (10Hz-100kHz) |
| PSRR | 80dB @ 1kHz, 60dB @ 100kHz |
| Quiescent Current | 1.2mA |
| Load Regulation | ±0.2% |
| Line Regulation | ±0.1% |
| Temperature Range | -40°C to +125°C |
| Package | SOT-23-5 |
Applications
ADC/DAC power supply
Power conversion and supply
RF circuit power
Electronic system design
Precision analog circuits
Electronic system design
Sensor power
Sensor signal conditioning
Audio circuits
Electronic system design
FAE Expert Insights
"The ACM7805 is my first choice for powering precision analog circuits. The 8μV noise floor is exceptional - I've measured it myself and it truly delivers on the datasheet spec. In one recent design for a medical device, we were struggling with ADC noise issues using a standard LDO. Switching to the ACM7805 reduced the noise floor by 15dB, allowing us to achieve the required 18-bit effective resolution. The PSRR is also genuinely excellent - I've seen it maintain 70dB+ even at 100kHz, which is critical for rejecting switching noise from upstream DC-DC converters. One important tip: the output capacitor selection matters more than you might think. While the datasheet specifies 4.7μF minimum, I recommend 10μF X7R ceramic for best transient response. Also, pay attention to the PCB layout - keep the output capacitor ground connection close to the LDO ground pin, not routed through the general ground plane. This minimizes ground bounce during load transients. For thermal management, remember that SOT-23-5 has limited heat dissipation capability. At 200mW+ dissipation, consider adding copper area or moving to a larger package. Overall, this is an outstanding LDO that competes with products costing 3x more."
Exceptional noise performance and PSRR make it ideal for precision analog applications
— Jennifer Liu, BeiLuo
Frequently Asked Questions
What makes the ACM7805 suitable for precision analog circuits?
The ACM7805 is specifically designed for noise-sensitive applications with several key features: Ultra-low output noise of 8μVrms (10Hz-100kHz) minimizes noise injection into analog circuits. High PSRR of 80dB at 1kHz effectively rejects input power supply noise. Excellent load and line regulation (±0.2% and ±0.1%) ensures stable output voltage under varying conditions. Low dropout voltage (200mV) allows operation with minimal headroom. These characteristics make it ideal for powering precision ADCs, DACs, RF circuits, and sensors where power supply noise directly impacts performance.
Use ACM7805 for any noise-sensitive analog circuit requiring clean, stable power supply.
How much input-output voltage difference is needed for proper regulation?
The ACM7805 requires a minimum dropout voltage of 200mV at 500mA load for proper regulation. At lighter loads, the dropout voltage is lower - approximately 100mV at 250mA. For reliable operation, maintain at least 300mV headroom (Vin - Vout) across all operating conditions including input voltage transients and temperature variations. For example, for 5V output, minimum input should be 5.3V. If your input voltage is only slightly higher than the desired output, consider using a lower dropout (LDO) version or a switching regulator for the pre-regulation stage.
Maintain at least 300mV headroom for reliable regulation across all conditions.
What capacitors are recommended for the ACM7805?
The ACM7805 requires specific capacitor types for stability and performance. Input capacitor: Use 10μF ceramic (X5R or X7R) close to the input pin to improve transient response and prevent oscillation. Output capacitor: Use 4.7μF ceramic with ESR < 1Ω for stability. Larger values (10μF) improve transient response. Bypass capacitor: Optional 0.1μF from BYP pin to ground reduces output noise. All capacitors should have voltage ratings at least 50% higher than the operating voltage. Place capacitors as close as possible to the respective pins with short trace lengths. Avoid tantalum capacitors as they have higher ESR.
Use 10μF ceramic on input, 4.7μF ceramic on output. Place close to pins.
How do I calculate thermal performance for the ACM7805?
Thermal calculation is critical for LDOs due to power dissipation. Calculate power dissipation: Pd = (Vin - Vout) × Iout + (Vin × Iq). For example: Vin=9V, Vout=5V, Iout=300mA: Pd = (9-5) × 0.3 + (9 × 0.0012) = 1.2 + 0.011 = 1.21W. Calculate junction temperature: Tj = Ta + (Pd × θja). For SOT-23-5, θja = 150°C/W. At Ta=50°C: Tj = 50 + (1.21 × 150) = 231°C (exceeds max 125°C). This configuration requires heat sinking or reduced current. Solutions: reduce input voltage, reduce output current, add copper area for heat sinking, or use a switching pre-regulator to reduce dropout voltage.
Always perform thermal calculations. Add copper area or reduce Vin-Vout for high current.
Can the enable pin be used for sequencing multiple LDOs?
Yes, the ENABLE pin can be used for power sequencing and management. The ENABLE pin is active high with 1.2V threshold. Connect to input voltage for always-on operation, or to a logic signal for on/off control. For sequencing multiple LDOs, connect the output of one LDO (through a voltage divider if needed) to the ENABLE of the next LDO. This creates a power-up sequence where downstream regulators turn on after upstream regulators are stable. The ENABLE pin has 1μA pull-down current, so a 10kΩ pull-up resistor is recommended when driven by open-drain signals. Enable switching time is approximately 100μs.
Use ENABLE pin for power sequencing. Connect upstream output to downstream ENABLE.
What is the difference between the ACM7805 and a standard 7805?
The ACM7805 is a modern CMOS LDO with significant advantages over legacy 7805 linear regulators: 1) Much lower dropout voltage: 200mV vs 2V typical, allowing operation with lower headroom. 2) Lower quiescent current: 1.2mA vs 5mA, better for battery applications. 3) Much lower output noise: 8μV vs hundreds of μV, critical for precision analog. 4) Higher PSRR: 80dB vs 60dB, better noise rejection. 5) Smaller package: SOT-23-5 vs TO-220. 6) Enable pin for power management. The main trade-off is lower maximum current (500mA vs 1A) and lower maximum input voltage (16V vs 35V). For modern designs, the ACM7805 offers superior performance in a smaller footprint.
Use ACM7805 for new designs requiring low noise and low dropout. Use standard 7805 for high current (>500mA) or high voltage (>16V).