Low current consumption, improved common mode transient immunity, and high transmission delay accuracy

Providing robust and reliable solutions for high-voltage digital control applications

■ Leakage current prevention, effective galvanic insulation is important

In high-voltage applications, effective galvanic isolation is important to prevent unwanted leakage currents between two system parts at different ground potentials.

The left side of Figure 1 shows that DC return current from input to output can cause a potential difference between the two grounds, which can degrade signal integrity and cause quality degradation.

In this case, an isolator (isolated gate driver IC [2] or digital isolator) plays an important role.

The right side of Figure 1 shows this. An isolator blocks DC and uncontrolled AC current between two circuit parts, allowing only communication signals and power to pass through the insulating barrier.

Isolators not only provide the necessary safety protection for workers working with high-voltage systems, they can also perform level-shifting functions to allow interaction between systems operating at different supply voltage levels.

▲Figure 1: DC return current flowing between two system parts creates an unwanted ground loop (left). Galvanic isolation prevents unwanted ground loops by breaking the ground connection (right).

Isolators can be broadly divided into two types: optical isolators and digital isolators.

Optical isolators, commonly referred to as optocouplers, are analog isolation products that use light to transmit signals through an insulating barrier. Optical isolators have been widely used in industrial applications for decades due to their long-standing presence in the market and their excellent price competitiveness.

However, the switching speed of LEDs limits the achievable data rates to just a few megabits per second.

Additionally, optical isolators require additional circuit components on the board for proper biasing and driving the LED.

This takes up additional PCB area and increases the bill of materials (BOM) of the application.

Although there are techniques to integrate external biasing and driving circuitry into a single package to minimize PCB area and achieve high data rates, these solutions are expensive.

Digital isolators, on the other hand, transmit signals across an isolation barrier using capacitive or magnetic isolation technology. These technologies significantly reduce the size of insulating elements and extend their lifespan [3].

Compared to optical isolators, digital isolators are preferred in many recent applications due to the following advantages:

- Optimize system BOM and reduce PCB area

- Accurate timing characteristics and low power consumption

- Improved common mode transient immunity (CMTI)

- Guaranteed insulation life according to component dimension standard IEC 60747-17

- Integration of additional features such as input filters, transceivers (CAN, RS-485, etc.), and output enable options

Table 1 summarizes the differences between optical and digital isolators.

▲Table 1: Differences between optical isolators and digital isolators

■ Infineon's 1st generation ISOFACE™ digital isolator 2DIBx4xxF

To meet the increasing insulation requirements for industrial applications, Infineon has developed the first generation2_ap_kr_pss_pss.ps.p.di&utm_content=e4ds&utm_term=tech+article_safe_isolation_low_power" target="_blank">Introducing a family of dual-channel digital isolators. These products feature high robustness, precise timing performance, and low power consumption.

These products feature Infineon’s patented coreless transformer (CT) technology. This innovative technology integrates an on-chip transformer made of a metal spiral using semiconductor manufacturing processes and separates it from the rest with a silicon dioxide (SiO2) insulating wall (Figure 2). This approach transmits the signal between the input and output through a transformer in an insulating wall.

▲Figure 2: Cross-sectional view of the coreless transformer used in Infineon’s ISOFACE™ digital isolator 2DIBx4xxF product

In addition, it includes features such as glitch filter, communication modulation, watchdog, and undervoltage lockout (UVLO), enabling robust and reliable data transmission even in challenging industrial environments where high voltages and noise exist.

Table 2 shows products in this family with different channel configurations, fail-safe default output states, and variable or fixed input limits.

▲Table 2: Product composition of the ISOFACE™ dual-channel digital isolator 2DIBx4xxF family

This family of dual-channel digital isolators is certified at component level to UL-1577 and IEC 60747-17 (VDE 0884-17) standards, and system level to IEC 62368-1 for telecom and server applications. Additionally, the 4 mm creepage and clearance distances make it well suited for applications requiring basic isolation such as low-voltage DC-DC bricks, top-side floating drives, and isolated UART/CAN communications.

Table 3 summarizes the product features and benefits of Infineon's ISOFACE™ dual-channel digital isolators.

▲Table 3: Product features and benefits of ISOFACE™ dual-channel digital isolator

■ Application examples of ISOFACE™ dual-channel digital isolators

○ Insulated low voltage DC-DC brick

Low-voltage DC-DC bricks are widely used to achieve stable 12VDC output from switched mode power supplies (SMPS) in telecom and servers [4].

To meet the ever-increasing demands for power density, safety, and communication capacity, isolated DC-DC bricks above 800 W primarily use the full-bridge-to-full-bridge (FB-FB) topology.

Control is handled by a digital controller located on the secondary side of the main power transformer. Digital isolators with basic insulation performance are commonly used to transmit PWM gate control signals across an isolation barrier with input-to-output safety isolation.

Figure 3 shows Infineon’s solution for an isolated 1kW DC-DC brick. The XDP™ XDPP1100 digital power controller on the secondary side is used to control the primary side full-bridge topology.

The ISOFACE™ dual-channel digital isolator 2DIB0410F transmits PWM signals across an isolation barrier.

▲Figure 3: Isolated low-voltage DC-DC brick adopting ISOFACE™ 2DIB0410F

This converter uses level-shifting EiceDRIVER™ 2EDL802x gate driver ICs on both sides.

Two channels of the digital isolator deliver complementary PWM signals to control two OptiMOS™ power MOSFETs diagonally across each arm of the full bridge.

Additionally, the ISOFACE™ 2DIB0410F provides fixed TTL input limits. Therefore, it increases the immunity to VDD power line noise in SMPS applications.

The default low output state safely turns off all MOSFETs when the input supply to the digital isolator is below UVLO.

○ Isolated CAN and UART communication

CAN (Controller Area Network) and UART (Universal Asynchronous Receiver/Transmitter) communications are widely used in industrial and automotive applications.

A common advantage is that only one pair of cables (two communication lines) is required at the physical layer for data transmission.

To ensure safety and prevent noise interference with isolated CAN or UART interfaces, the ISOFACE™ dual-channel digital isolator 2DIB1401F provides an excellent solution for galvanic isolation.

This reliable isolator features high CMTI and extremely low pulse width distortion (PWD), which are important for achieving reliable communications.

Additionally, this isolator prevents any potential power loss on the input side by ensuring that the communication line (normally logic high when idle) is not interrupted even if a fault occurs in the default high output state.

Figure 4 shows an example of an isolated CAN interface using Infineon's CAN transceiver TLE9251. ISOFACE™ 2DIB1401F provides galvanic isolation between the controller and transceiver.

▲Figure 4: Isolated CAN (Controller Area Network) communication using ISOFACE™ 2DIB1401F

○ Functional isolation of GaN IPS half bridge

In recent years, 650V gallium nitride (GaN) HEMTs have become increasingly important in SMPS designs because they can operate at much higher switching frequencies and minimize energy losses. GaN IPS (Integrated Power Stage), which integrates GaN switches and gate drivers in a single package, is also gaining popularity because it can achieve extremely high power density, reduce component count, and minimize parasitic components.

For proper operation of the upper GaN IPS, a digital isolator is required for level shifting function as a gate driver. This is because the gate driver refers to the switching node. Since GaN HEMT generates fast dv/dt communication up to 100 V/ns, high common mode transients can occur. Therefore, a robust solution is required. ISOFACE™ digital isolators reliably transmit PWM signals with a CMTI of at least 100 V/ns.

Figure 5 shows an example using the ISOFACE™ dual-channel digital isolator 2DIB1410F as a top-side floating drive. The forward data channel carries the gate signal, and the reverse channel communicates the fault feedback signal to the controller.

Optionally, another ISOFACE™ 2DIB1410F can be used with bottom GaN IPS. This is strongly recommended to ensure equal propagation delay between the high-side and low-side signal paths and to provide isolation between the different grounds of the GaN IPS (power ground) and the controller (digital ground).

▲Figure 5: Functional isolation using ISOFACE™ 2DIB1410F with GaN IPS half bridge

■ Conclusion

Infineon's leading ISOFACE™ digital isolators feature low current consumption, improved common-mode transient immunity and high propagation delay accuracy, providing a robust and reliable solution for high-voltage digital control applications.

By combining this with other Infineon products such as XDP™ digital controllers, EiceDRIVER™ gate driver ICs and power switches (OptiMOS™, CoolMOS™, CoolSiC™, CoolGaN™), a complete system solution can be achieved that meets the increasing isolation requirements of modern power electronics applications.

Infineon's leading technology will enable customers to meet increasing isolation requirements for high-voltage digital control applications, achieving better system performance and higher reliability.

.infineon.com/cms/en/product/isolation/digital-isolators/?utm_source=e4ds&utm_medium=referral&utm_campaign=202402_ap_kr_pss_pss.ps.p.di&utm_content=e4ds&utm_term=tech+article_safe_isolation_low_power" target="_blank">Click here for more information on Infineon's ISOFACE™ digital isolators.

※ author

Jiaxin Tian, Senior Staff Product Application Engineer,

Dr. Narayanaswamy Swaminathan, Staff Product Definition Engineer,

Dr. Diogo Varajao, Head of Technical Marketing of Isolation ICs,

Infineon Technologies

※ References

[1] D. Varajao, C. Menditti Matrisciano, "Isolated gate driving solutions - Increasing power density and robustness with isolated gate driver ICs," Infineon Technologies AG, Application Note v1.1, AN_1909_PL52_1010_201256, June 2022

[2] C. Menditti Matrisciano, T. Beer, D. Varajao, Infineon Technologies AG, "Using the EiceDRIVER™ 2EDi product family of dual-channel functional and reinforced isolated MOSFET gate drivers," Infineon Technologies AG, AN_1805_PL52_1806_095202, 2019

[3] W. Frank, H. Rettinger, “New International Standard for Magnetic and Capacitive Couplers,” Bodo's Power Systems, November 2020, p. 40-43

[4] D. Varajao, C. Menditti Matrisciano, "Dual-channel isolated EiceDRIVER™ 2EDF7275K in telecom bricks - Application example in a 600 W quarter-brick 48 V to 12 V full-bridge to full-bridge rectifier evaluation board," Infineon Technologies AG, AN_2002_PL52_2003_165036, 2020