MAX7461EUK+T is a low-power, 8th-order, switched-capacitor (SC) low-pass filter designed and manufactured by Maxim Integrated (now part of Analog Devices since 2021). It belongs to the highly integrated MAX746x family, engineered specifically for anti-aliasing and reconstruction filtering in precision data acquisition systems, where sharp roll-off, precise cutoff frequency control, rail-to-rail operation, and minimal external components are essential — especially in battery-powered, space-constrained, or cost-sensitive applications.
The “EUK” suffix denotes the 5-lead SOT-23 package (2.9 mm × 1.6 mm) — an ultra-compact, surface-mount footprint; the “+T” indicates tape-and-reel packaging (3,000 units per reel), Pb-free, RoHS-compliant, and qualified for –40°C to +85°C ambient temperature.
โ ๏ธ Critical Clarification:
The MAX7461 is not a general-purpose op-amp-based active filter or digital FIR filter. It is a fully integrated, clock-tunable, 8th-order elliptic (Cauer) low-pass filter, featuring:
- Fixed 8th-order response with 0.5 dB passband ripple, −55 dB stopband attenuation, and sharp transition band (typ. 1.8× fC) — ideal for anti-aliasing before high-resolution ADCs (e.g., 16–24-bit sigma-delta);
- Precise, programmable cutoff frequency (fC) set solely by an external master clock (CLK):
fC = fCLK / 100 (for MAX7461), with ±0.5% typical accuracy over temperature and supply — no external resistors/capacitors needed for tuning;
- True rail-to-rail I/O: Input and output swing from VSS to VDD, supporting single-supply operation from 2.7 V to 3.6 V, making it ideal for modern low-voltage microcontrollers and sensors;
- Ultra-low power: Only 60 µA quiescent current (typ.), enabling multi-year battery life in portable instrumentation and IoT edge nodes;
- No external passive components required beyond decoupling caps — eliminating component tolerance errors, board space, and calibration overhead.
It features internal clock generation (if external CLK not provided), shutdown mode (< 1 µA), and robust ESD protection — all in a microscopic 5-pin SOT-23.
Introduction
The MAX7461EUK+T delivers laboratory-grade analog filtering performance in the smallest possible footprint:
๐น 8th-order elliptic response in 2.9 mm × 1.6 mm: Replaces complex multi-stage op-amp filters requiring ≥ 10 discrete components — reducing BOM cost, layout area by >80%, and sensitivity to component drift;
๐น Clock-defined precision: With fC = fCLK/100, a stable 1 MHz crystal or MCU timer yields exactly 10 kHz cutoff ±0.5% — far more accurate than RC-based filters (±5–10% typical);
๐น Zero-component tuning: No external R/C network means no temperature drift, aging, or layout parasitics affecting fC — ideal for production calibration-free designs;
๐น Battery-optimized operation: 60 µA IQ at 3 V, rail-to-rail I/O, and shutdown mode make it perfect for always-on sensor front-ends and portable DMMs.
Its SOT-23-5 (EUK) package is widely supported by automated assembly and enables placement directly adjacent to ADCs or sensors — minimizing noise pickup and trace inductance.
Key Features
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High-Performance 8th-Order Filtering:
• Filter type: Elliptic (Cauer), low-pass;
• Order: 8th-order (equivalent to four 2nd-order stages);
• Passband ripple: 0.5 dB (max);
• Stopband attenuation: ≥ –55 dB;
• Transition ratio (fSTOP/fC): 1.8 (typ.), < 2.2 (max).
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Precision Clock-Tuned Cutoff Frequency:
• Relationship: fC = fCLK / 100;
• fC range: 1 Hz to 10 kHz (with fCLK = 100 Hz to 1 MHz);
• Accuracy: ±0.5% (typ.), ±1.5% (max) over temp/supply;
• Clock input: CMOS-compatible, accepts square wave or MCU GPIO output.
โ
Low-Power & Single-Supply Operation:
• Supply voltage: 2.7 V to 3.6 V (optimized for Li-ion/coin cell systems);
• Quiescent current: 60 µA (typ.), 100 µA (max);
• Shutdown current: < 1 µA;
• Rail-to-rail input/output: supports full 0–VDD signal swing.
โ
Robust Integration & Protection:
• Internal clock oscillator (optional): eliminates need for external clock if precision relaxed (±5% fC);
• ESD rating: > 2 kV HBM on all pins;
• No external resistors or capacitors required for filter function.
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SOT-23-5 (EUK) Package & Industrial Qualification:
• 5-Lead SOT-23 (2.9 mm × 1.6 mm);
• RoHS-compliant, Pb-free, halogen-free;
• Operating ambient temperature: –40°C to +85°C;
• JEDEC J-STD-020 MSL 1 — unlimited floor life.
Typical Specification Table
| Parameter |
Specification |
| Manufacturer |
Analog Devices (formerly Maxim Integrated) |
| Product Series |
MAX746x Family (Switched-Capacitor Filters) |
| Model |
MAX7461EUK+T |
| Function |
8th-Order Elliptic Low-Pass Filter |
| Filter Type |
Low-pass, elliptic (0.5 dB ripple) |
| Cutoff Frequency (fC) |
fCLK/100; 1 Hz – 10 kHz (typ.) |
| fC Accuracy |
±0.5% (typ.), ±1.5% (max) over temp/supply |
| Stopband Attenuation |
≥ –55 dB |
| Transition Ratio (fSTOP/fC) |
1.8 (typ.), < 2.2 (max) |
| Supply Voltage |
2.7 V to 3.6 V |
| Quiescent Current |
60 µA (typ.), 100 µA (max) |
| Shutdown Current |
< 1 µA |
| I/O Swing |
Rail-to-rail (VSS to VDD) |
| Package |
5-Lead SOT-23 (2.9 mm × 1.6 mm) (EUK) |
| RoHS / Green |
Yes (Pb-free, Halogen-free) |
| Packaging |
Tape-and-Reel, 3,000 units (+T) |
Typical Applications
๐น Anti-Aliasing for High-Resolution ADCs: Front-end filtering for 24-bit sigma-delta converters (e.g., AD7177, ADS127L01) — leveraging sharp 8th-order roll-off and precise fC to prevent aliasing without oversampling penalties.
๐น Portable Test Equipment: Handheld DMMs, oscilloscope probes, and portable spectrum analyzers — enabled by ultra-low power, small size, and rail-to-rail operation from single Li-ion cells.
๐น IoT Sensor Nodes: Vibration, temperature, and acoustic monitoring — using clock-tuned fC to match Nyquist requirements of ultra-low-power MCUs (e.g., Silicon Labs EFR32, Nordic nRF52).
๐น Medical Instrumentation: ECG/EEG front-ends, pulse oximeters, and hearing aids — benefiting from low noise, precise cutoff, and low power for FDA-cleared wearable devices.
๐น Industrial Process Monitoring: Wireless pressure/flow transmitters and predictive maintenance sensors — where long battery life and calibration-free operation reduce maintenance costs.
๐น Audio Signal Conditioning: Pre-filtering for voice-band (300–3400 Hz) or ultrasonic (40 kHz) sensing — using programmable fC to adapt to different sensor bandwidths.
Development & Design Notes
๐ง PCB Layout Best Practices:
- Place the MAX7461 as close as possible to the ADC input — keep analog traces short (< 10 mm), avoid vias, and use ground guard rings to minimize noise coupling.
- Route CLK trace away from analog paths — add a series 33 Ω resistor near the MAX7461 CLK pin to damp ringing and reduce EMI.
- Use separate ground vias for GND and VDD — avoid daisy-chaining grounds to prevent digital noise injection.
๐ง Power Supply Decoupling:
- Place a 100 nF X7R ceramic capacitor within 1 mm of VDD and GND pins — critical for clean switching and low-noise performance.
- Add a 1 µF tantalum capacitor near the power entry point — improves low-frequency PSRR and reduces supply-induced ripple on fC.
๐ง Clock Source Selection & Timing:
- For highest fC accuracy: use a precision crystal oscillator (e.g., 1.000 MHz) or MCU timer with < 100 ppm stability;
- For cost-sensitive designs: use internal oscillator (pin 3 = GND) — fC ≈ fCLK(INT)/100 = ๏ฝ10 kHz ±5%;
- Ensure CLK duty cycle is 40–60% — avoids distortion in elliptic response.
๐ง Thermal Management & Reliability:
- SOT-23-5 has modest thermal capability (θJA ≈ 220°C/W). For continuous operation above +50°C ambient, add ≥ 50 mm² copper pour under the IC.
- FIT rate = 26 failures per billion hours, with FMEDA report supporting IEC 61508 SIL-2 — combine periodic self-test (e.g., inject known tone and verify attenuation) for functional safety.
๐ง Calibration & Accuracy Optimization:
- For metrology-grade applications, measure actual fC using a spectrum analyzer and store correction factor in firmware — achieves < 0.1% effective error.
- To minimize THD in audio paths, use matched external series resistors (e.g., 10 Ω) on IN/OUT — balances capacitive mismatch and improves linearity.
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