ADP7118AUJZ-R7CircuitDesignMasteringPSRRforNoise-SensitiveSystems
Why Do Precision Circuits Fail? Solving Power Noise with ADP7118AUJZ-R7
Engineers designing high-precision systems—from medical sensors to RF transceiver s—face a relentless enemy: power supply noise corrupting sensitive signals, voltage ripples triggering false readings, and thermal drift degrading calibration. The ADP7118AUJZ-R7—Analog Devices' 20V input, 200mA LDO regulator—boasts industry-leading 88dB PSRR at 10kHz and 0.42V dropout voltage, yet 68% of field failures trace to flawed circuit implementations in noise-critical applications. With analog systems demanding microvolt-level stability, mastering this LDO’s design isn’t optional—it’s the barrier between groundbreaking innovation and costly recalls.
⚡️ Core Advantages: Why ADP7118 Dominates Precision Power
1. Unmatched Noise Suppression
88dB PSRR at 10kHz slashes input ripple by 99.999%, outperforming rivals like TPS7A47 (75dB). This is critical for 24-bit ADC references where 100µV noise causes ±4 LSB errors.
11µVrms output noise (10Hz–100kHz) enables direct powering of sensitive op-amps without additional filtering.
2. Stability with Ceramic Capacitors
Unlike older LDOs requiring bulky tantalum caps, ADP7118 stabilizes with 2.2µF ceramic capacitor s—saving 60% PCB area.
3. Fault Resilience
Autorecovery thermal shutdown at 150°C and foldback current limiting prevent meltdowns during shorts.
Pro Tip: Pair with YY-IC’s EMI -optimized PCB layouts to achieve noise floors below 5µV.
🔧 Step-by-Step Circuit Design for 90dB+ PSRR
Step 1: Input Filtering
Problem: 100MHz switching noise from DC-DC converters couples into LDO inputs.
Solution:
复制Components:- Ferrite bead: 600Ω@100MHz (e.g., Murata BLM18PG601SN1)- Π-filter: C1=1µF (X7R), L=2.2µH, C2=10µF (X7R)Placement: ≤5mm from VIN pin (TSOT-23-5 Pin 1)
Critical: Route input traces as coplanar waveguides with 0.3mm ground gaps.
Step 2: Output Stability Tuning
Avoid capacitance >10µF: Excess capacitance causes phase margin drop → oscillation.
Add 10Ω damper resistor in series with Cout if using low-ESR (<5mΩ) ceramics.
Step 3: SENSE/ADJ Precision
For adjustable output (1.2V–19V):
复制
VOUT = 1.235V × (1 + R1/R2)Use 0.1% tolerance resistors; mismatch >0.5% degrades PSRR by 15dB.
🌡️ Thermal Management : Data-Driven Practices
Cooling Method | 200mA Load @12V Input | ΔT Reduction |
|---|---|---|
No copper pour | 125°C (⚠️ Thermal shutdown) | Baseline |
100mm² copper area | 85°C | 40°C |
+1m/s airflow | 65°C | 60°C |
Data source: ADP7118 datasheet thermal derating curves
Failure Analysis:
Overheating root cause: 75% due to missing copper pours under exposed pad (Pin 5).
Fix: Solder pad to ≥100mm² ground plane with 8 thermal vias (0.3mm diameter).
⚠️ Critical Pitfalls & Fixes
Pitfall 1: Floating SENSE Pin
❌ Unconnected SENSE/ADJ (Pin 2) causes output overshoot to 22V—destroying downstream ICs.
✅ Fix: Short to VOUT for fixed voltage, or connect to resistor divider.
Pitfall 2: EN Pin Glitches
Slow EN ramp rates >1ms trigger latch-up. Add 100nF capacitor to EN pin for >5V/µs slew rate.
Pitfall 3: Ground Loops
Shared ADC/LDO grounds introduce 50µV offsets. Star ground at LDO GND pin.
❓ Engineers' Top Questions
Q: Can it drive 300mA peaks?
✅ Yes—for ≤10ms bursts. Use YY-IC’s transient-tolerant layouts with 2oz copper.
Q: Why does PSRR drop above 100kHz?
Parasitic inductance in VIN trace dominates. Keep input filter within 3mm of pin.
Q: ADP7118 vs. LM317 for 5V systems?
ADP7118 wins:
PSRR: 50dB vs. 0dB at 100kHz
Dropout: 0.42V vs. 1.7V @200mA
Noise: 11µVrms vs. 400µVrms.
Final Insight: The ADP7118AUJZ-R7 isn’t just a regulator—it’s a signal integrity guardian. For engineers battling nanovolt noise floors, YY-IC electronic components one-stop support delivers beyond datasheets: their PSRR validation kits and thermal simulation reports transform 5mm² PCB areas into fortress-like power systems. Remember: In precision electronics, nanovolts define truth.
