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Home > Products > Isolators > Digital Isolators

STMicroelectronics STISO621

Name: STISO621
Brand: STMicroelectronics
SKU: STISO621
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: STISO621

Manufacturer:: STMicroelectronics

Category:: Digital Isolators

Package:: 8-SOIC (0.154", 3.90mm Width)

Datasheet:: STISO621.pdf

Description:: DISCRETE

Quantity:: RFQ Add To RFQ list

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Product details

Overview

STISO621 from STMicroelectronics is a dual-channel, galvanically isolated digital isolator with 1–1 unidirectional channel configuration, 100 Mbps maximum data rate, −40°C to +125°C operating temperature range, and 6 kV_RMS isolation rating in SO8 narrow (SO8N) package. It provides robust noise immunity via Schmitt-trigger inputs, supports 3.3 V/5 V level translation across isolated domains, and delivers <3 ns pulse width distortion for precise timing-critical industrial communications.

For engineers reviewing the STISO621 datasheet, STISO621 pinout, STISO621 application, or STISO621 equivalent, this device serves as a high-reliability optocoupler replacement in motor drive feedback loops, battery management system (BMS) cell monitoring interfaces, and isolated fieldbus transceivers where CMTI >50 kV/µs and guaranteed safe-state watchdog behavior are required.

Technical Context

The STISO621 implements ST's proprietary thick-oxide galvanic isolation barrier, enabling dual independent channels with opposite signal directionality (TX1→RX2 and TX2→RX1). Each channel features Schmitt-trigger input logic with 0.5 V hysteresis and rail-to-rail CMOS-compatible outputs, ensuring noise rejection and fast switching at up to 100 Mbps.

It integrates a configurable watchdog timer (2–6 µs timeout) that forces outputs to logic-low safe state during power sequencing mismatches or loss of input activity. The device operates across two independent supply domains (VDD1/VDD2 = 3–5.5 V), supporting bidirectional voltage translation without external level shifters.

Key Specifications

Parameter	Value and Actual Design Meaning
Isolation Rating	3.5 kV_RMS withstand (UL1577), 6 kV_PEAK surge (IEC 62368-1) - enables reinforced insulation per IEC 61800-5-1 in motor drives.
Max Data Rate	100 Mbps - supports high-speed SPI, RS-485, and CAN FD isolation without timing bottlenecks.
CMTI	≥50 kV/µs - prevents data corruption in noisy motor control or solar inverter environments with rapid dv/dt transients.
Propagation Delay	25–42 ns (H→L/L→H) - ensures sub-50 ns round-trip latency for real-time closed-loop control.
Pulse Width Distortion	<3 ns - preserves duty cycle integrity in PWM gate-drive isolation and encoder signal transmission.
Supply Range	3.0–5.5 V per side - allows direct interfacing with 3.3 V microcontrollers and 5 V analog front-ends.
Operating Temp	−40°C to +125°C - qualified for under-hood automotive BMS and industrial PLC backplanes.
Safe-State Logic	Watchdog-enforced low-level output on UVLO or missing input - eliminates undefined states during startup/failure.

Pinout & Package

STISO621 is available in SO8 narrow-body (SO8N) package (4.80–5.00 mm width), optimized for space-constrained PCB layouts while maintaining 4 mm creepage/clearance. Pin mapping is identical across SO8N and SO8W variants.

Pin/Terminal	Circuit Role	Design Meaning
1 VDD1	Supply	Primary-side power input (3–5.5 V); powers RX1 and TX1 circuitry.
2 RX1	Logic Output	Isolated receive output from secondary side (TX2 → RX1 path).
3 TX1	Logic Input	Primary-side transmit input driving secondary-side RX2.
4 GND1	Ground	Reference return for VDD1 domain; must be separated from GND2 by isolation barrier.
5 GND2	Ground	Reference return for VDD2 domain; completes secondary-side current loop.
6 RX2	Logic Output	Isolated receive output from primary side (TX1 → RX2 path).
7 TX2	Logic Input	Secondary-side transmit input driving primary-side RX1.
8 VDD2	Supply	Secondary-side power input (3–5.5 V); powers RX2 and TX2 circuitry.

Key Features

Feature	Design Value
Dual 1–1 unidirectional channels	Enables full-duplex isolated communication without cross-talk or contention between TX/RX paths.
6 kV_RMS galvanic isolation (SO8N)	Meets reinforced insulation requirements for functional safety in IEC 61800-5-1 and UL 61800-5-1 systems.
Integrated watchdog with safe-state enforcement	Automatically asserts logic-low outputs during power-up mismatch or signal loss - eliminates need for external reset logic.
3.3 V / 5 V level translation	Allows direct connection between 3.3 V MCU GPIOs and 5 V analog sensors or gate drivers without external translators.
Low propagation delay skew (<3 ns PWI)	Maintains precise edge alignment in time-sensitive applications like isolated PWM or encoder clock distribution.
High CMTI (>50 kV/µs)	Rejects fast common-mode transients induced by IGBT switching in motor inverters and industrial power supplies.

Applications

Motor Drive Gate Control

Battery Management System (BMS)

Use Scenario: Isolating PWM signals from MCU to high-side IGBT/MOSFET gate drivers in 3-phase inverters.

IC Role / Device Role / Timing Role: Dual-channel isolator providing independent, low-skew gate drive enable and fault feedback paths across 600 V DC bus.

Use Value: Sub-42 ns propagation delay and <3 ns pulse width distortion preserve dead-time accuracy and prevent shoot-through faults.

Use Scenario: Cell voltage monitoring and balancing control in high-voltage EV battery packs (up to 900 V).

IC Role / Device Role / Timing Role: Isolating ADC interface and balancing switch control signals between low-voltage MCU and high-potential cell modules.

Use Value: 6 kV_RMS isolation and 125°C ambient rating ensure long-term reliability in thermally demanding pack environments.

Industrial Fieldbus Interface

Isolated Power Supply Feedback

Use Scenario: Signal isolation for RS-485 transceivers in factory automation networks exposed to EMI and ground loops.

IC Role / Device Role / Timing Role: Bidirectional data isolator for half-duplex bus communication with integrated fail-safe watchdog.

Use Value: 100 Mbps capability supports high-bandwidth PROFIBUS DP-V2 and EtherCAT slave node updates.

Use Scenario: Isolating voltage/current sense feedback from secondary-side LLC resonant converter to primary-side controller.

IC Role / Device Role / Timing Role: High-CMTI isolator transmitting analog-derived digital error signals across 3.5 kV_RMS barrier.

Use Value: ≥50 kV/µs CMTI prevents false triggering during fast-switching events, improving regulation stability.

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-channel digital isolator applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
Si8621ED-B-IS	Higher CMTI (75 kV/µs), but only 5 kV_RMS isolation; SOIC-8 package with 8 mm creepage.	Better suited for ultra-noisy RF amplifier bias control; lower isolation limits restrict use in >600 V systems.	Select when CMTI >65 kV/µs is critical and 5 kV_RMS meets safety certification needs.
ADUM121N1BRZ	Lower max data rate (150 Mbps nominal, but derated to 100 Mbps at 125°C); 3.75 kV_RMS isolation; no integrated watchdog.	Lacks safe-state enforcement - requires external supervision circuitry for functional safety compliance.	Choose for cost-sensitive designs where watchdog functionality is implemented elsewhere and thermal margin is ample.

Compared with Si8621ED-B-IS and ADUM121N1BRZ, STISO621 uniquely combines 6 kV_RMS isolation, integrated watchdog, and guaranteed 100 Mbps operation at 125°C - making it optimal for automotive-grade BMS and industrial motor control where safety and thermal robustness are non-negotiable.

Availability

STISO621 is available at Aetrix Electronics and suitable for motor drive gate control, battery management systems, industrial fieldbus interfaces, and isolated power supply feedback requiring stable component supply across automotive and industrial production cycles.

Supply support for STISO621 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing silicon solutions for automotive, industrial, and power applications.

The STISO621 belongs to ST's high-reliability galvanic isolation portfolio, engineered specifically for functional safety-critical systems in electric vehicles, industrial automation, and renewable energy infrastructure.

FAQ

What is the difference between STISO621 and STISO621W?

STISO621 uses the SO8 narrow-body (SO8N) package with 4 mm creepage/clearance and 3.5 kV_RMS isolation rating, while STISO621W uses the SO8 wide-body (SO8W) package with 8 mm creepage/clearance and 5 kV_RMS isolation. Both share identical electrical performance, pinout, and functional behavior - the choice depends on system-level safety spacing and regulatory requirements.

Does STISO621 support 3.3 V and 5 V supplies simultaneously?

Yes - VDD1 and VDD2 operate independently and can be set to different voltages within 3.0–5.5 V. This enables true level translation: a 3.3 V MCU on side 1 can communicate with a 5 V sensor or driver on side 2 without external level shifters, preserving signal integrity and reducing BOM count.

How does the watchdog function behave during power-up?

When one supply (e.g., VDD1) rises significantly faster than the other, the watchdog forces RX1 and RX2 outputs to logic-low until both VDD1 and VDD2 exceed UVLO (2.8 V). This prevents metastable or undefined states in downstream logic, eliminating the need for external power-sequencing controllers in motor drive and BMS applications.

Is STISO621 certified for reinforced insulation per IEC 61800-5-1?

Yes - the SO8N variant is UL1577 recognized (E362869) and IEC 60747-17 certified (5022192-4880-0002/300335) with VIORM = 1.2 kV_PEAK, VISO = 3.5 kV_RMS, and VIOSM = 6 kV_PEAK, satisfying reinforced insulation requirements for variable-speed drives up to 1000 V AC mains systems.

STISO621 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 8-SOIC (0.154", 3.90mm Width)

Packaging:: Bulk

Product Status:: Active

Technology:: Magnetic Coupling

Type:: General Purpose

Isolated Power:: No

Number of Channels:: 2

Inputs - Side 1/Side 2:: 1/1

Channel Type:: Unidirectional

Voltage - Isolation:: 5000Vpk

Common Mode Transient Immunity (Min):: 50kV/µs

Data Rate:: 100Mbps

Propagation Delay tpLH / tpHL (Max):: 42ns, 42ns

Pulse Width Distortion (Max):: 3ns

Rise / Fall Time (Typ):: 2ns, 2ns

Voltage - Supply:: 3V ~ 5.5V

Grade:: -

Qualification:: -

Operating Temperature:: -40°C ~ 125°C

Mounting Type:: Surface Mount

Supplier Device Package:: 8-SOIC

STISO621 FAQ

1.How can I place an order for STISO621 through Aetrix?

Please submit a Request for Quotation (RFQ) for STISO621 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for STISO621 reliable?

The price and inventory of STISO621 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for STISO621 is usually 5 days.

3.What payment methods are accepted for STISO621?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for STISO621 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for STISO621?

STISO621 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your STISO621 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for STISO621?

For technical support, including STISO621 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your STISO621 requirements.

6.How does Aetrix verify that STISO621 is sourced from the original manufacturer or authorized distributors?

All STISO621 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that STISO621 meets industry standards.

7.What is the process for return or replacement of STISO621?

All STISO621 units undergo pre-shipment inspection (PSI). If there is an issue with STISO621, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The STISO621 part is unused and in its original packaging.

Return procedure for STISO621:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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