All three are 25 MBd high-speed digital optocouplers using a CMOS-driver, CMOS-detector architecture. Their inputs accept logic levels directly with no external LED current-limiting resistor (CMOS input), needing only two bypass capacitors to run. Typical uses: digital fieldbus isolation (CC-Link, DeviceNet, PROFIBUS), isolated SPI/UART, signal isolation in motor drives and inverters, and microprocessor interfaces.

Same speed class, so the difference is not raw speed but three things: common-mode noise immunity (CMR), supply voltage, and original part versus second source. The HCPL-0720 is a mature 5V standard part; the FOD0720 is pin-compatible with it, focused on supply and cost while improving CMR and temperature range; the ACPL-077L moves to the 3.3V/5V domain, pushes CMR to the highest level, and adds system-level immunity. Choose by supply voltage, noise environment, and supply-chain strategy together.

Parameter Comparison

All three have CMOS logic inputs, so a traditional optocoupler’s LED trigger current does not apply. tP is a max value; actual typ is lower (ACPL-077L ≈ 24 ns). CMR values are datasheet minimums at VCM=1000V.

Application Scenarios

• HCPL-0720

It is the best-documented standard part in this speed class, with most high-speed-optocoupler app notes based on its family (HCPL-072x/772x). In 5V designs with controlled noise, it is the low-risk default. Its limits: CMR of only 10 kV/µs—the smallest margin—and no 3.3V support.

Best for:

• • 5V digital-bus isolation in controlled-noise environments
  • Projects reusing an existing HCPL-072x/772x design
  • Isolated UART/SPI and microprocessor interfaces
• FOD0720

Pin-compatible with the HCPL-0720 and parameter-aligned, its main value is procurement—avoiding single-supplier risk and controlling cost. But it is no plain equal: CMR rises to 20 kV/µs and temperature extends to +100°C, with more transparent pricing. Switching from the HCPL-0720 is usually equal-or-better, not a compromise.

Best for:

• • Establishing a second source for an HCPL-0720 design
  • Cost-sensitive, higher-volume 5V isolated signal chains
  • Industrial and power scenarios needing +100°C operation
• ACPL-077L

The highest-performance of the three, with two distinctions. Supply: 3.3V/5V, interfacing directly with FPGA/MCU low-voltage I/O and enabling level shifting. Immunity: CMR up to 35 kV/µs with system-level ESD/Burst/Surge enhancement, plus lower PWD. It suits low-voltage digital systems and noisy motor-drive or inverter environments.

Note: it is electrically compatible with the other two but uses a different supply domain. It runs if kept at 5V, but exploiting its 3.3V advantage means replanning supply and levels—not a direct drop-in for a 5V design.

Best for:

• • Isolation interfaces in 3.3V FPGA/MCU systems
  • High common-mode-noise environments such as inverters and motor drives
  • Industrial/medical front ends with hard system-level immunity requirements

Design Considerations

• CMR sets the bit-error margin in noisy environments

CMR measures whether the device holds its output when a fast voltage step crosses the barrier. In tens-of-kV/µs motor-drive and inverter environments, it directly affects bit-error rate. The three climb 10→20→35 kV/µs, leaving the HCPL-0720 the smallest margin. Datasheet values are specified at VCM=1000V, 25°C; real performance also depends on layout, ground bounce, and trace coupling.

• Propagation delay and PWD set the usable timing margin

All three rate 25 MBd at 40 ns delay, but pulse-width distortion differs: 8 ns for HCPL-0720/FOD0720, 6 ns for ACPL-077L. PWD—the gap between high-to-low and low-to-high delay—eats directly into the receiver’s decision window. Near full speed, or across long or cascaded links, lower PWD means steadier timing; this is a quiet advantage of the ACPL-077L in high-accuracy transmission.

• Bypass capacitors are a prerequisite, not optional

All three require a 0.01–0.1 µF bypass capacitor on each supply pin, placed tight to the pins. High-speed CMOS switching draws large transient currents; inadequate bypassing causes jitter, false triggering, or even CMR collapse—the most common and most overlooked root cause of intermittent bit errors.

• Confirm supply domain and parameter alignment before switching

The HCPL-0720 and FOD0720 are 5V-only and malfunction on 3.3V; the ACPL-077L’s 3.3V/5V support makes it the choice for cross-voltage migration. Pin-compatible second-sourcing still warrants an item-by-item check of CMR, temperature, and safety against the original margin—here the FOD0720 meets or beats the HCPL-0720 on every count.

Selection Recommendations

• For 5V supply, controlled noise, and a priority on documentation and long-term supply, choose the HCPL-0720—the safe default for this speed class.
• For an existing HCPL-0720 design needing a second source or lower cost, choose the FOD0720—a pin-compatible, better-spec’d second source.
• For a 3.3V platform, noisy environment, or hard system-level immunity requirement, choose the ACPL-077L—flexible supply and the highest CMR, though a premium choice in pure-5V, low-noise designs.

Product Summary

WIN SOURCE supplies high-speed digital optocouplers and related isolated signal-chain devices from Broadcom and onsemi for industrial bus, motor drive, power isolation, and digital-interface designs. Visit WIN SOURCE to check real-time stock and availability for the HCPL-0720, FOD0720, and ACPL-077L.